Paralava and clinker products of coal combustion, Yellow River, Shanxi Province, China

This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies areencouraged to visit:

http://www.elsevier.com/copyright

http://www.elsevier.com/copyright

Author's personal copy

Paralava and clinker products of coal combustion, YellowRiver, Shanxi Province, China

Rodney Grapes a,⁎, Ke Zhang b, Zhuo-lun Peng b

a Department of Earth and Environmental Sciences, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 136-701, Republic of Koreab Department of Earth Sciences, Sun Yat-sen University, Guangzhou, China

a b s t r a c ta r t i c l e i n f o

Article history:Received 5 March 2009Accepted 13 July 2009Available online 23 July 2009

Keywords:Coal combustionParalavaClinkerYellow RiverShanxi ProvinceChina

Combustion of bituminous coal seams in a Carbonifeorus–Permian sequence of siltstone, quartzose sand-stone, sideritic mudstone, kaolinite-rich and sulphide–ankerite rocks exposed on the left bank of the YellowRiver, western border of Shanxi Province, China, has resulted in the formation of paralava and glassy clinker.Some paralavas have compositions similar to low alkali basalts and contain anorthite, low Ca-pyroxenes(clinoenstatite, pigeonite), ±minor augite, ±olivine, Fe–Ti oxides and K-bearing siliceous glass. In theseparalavas the sequence of pyroxene crystallization was Mg-pigeonite→augite→Fe-pigeonite and Mg-clinoenstatite→borderline Fe-clinoenstatite/pigeonite. More siliceous paralava compositions containanorthite, clinoenstatite, cordierite, Fe–Ti oxides and glass. Fused clinker consists of cordierite, anorthite,tridymite, mullite, Fe–Ti oxides and K-rich siliceous glass. Paralava liquidus temperatures range between ca.1230 and 1120 °C and the generalized crystallization sequence in a “basaltic” composition was anorthite,pyroxene (low Ca-clinopyroxene, augite), Ti-magnetite, olivine with quench apatite in glass over a coolinginterval of ∼345 °C. The liquidus temperature of clinker was ca. 1100 °C. In paralavas and clinker, subsolidusexsolution of hemo-ilmenite from Ti-magnetite occurred under logfO2=−9.0 to −13.9 at temperatures of907–756 °C, with formation of almost pure ilmenite at lowest temperatures of 536–567 °C at logfO2=−24.9–21.9. Changes in the texture and habit of pyroxene in paralava adjacent clinker (porphyritic toskeletal/plumose towards clinker) reflect the effects of a cooling front moving into the paralava and changingbulk composition. Paralavas formed by melting of different combinations of siltstone, sideritic mudstone andankerite-rich rock “end-members”, and there was also diffusion of Si, Al, Ti and K into paralava from fusedclinker blocks within it.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

The generation of melted (glassy) rocks during high temperature/lowpressure pyrometamorphismof sediments caused by spontaneouscombustionof coal, carbonaceous sediments or gas is a commonpheno-menon (see Grapes, 2006 and references therein). Such rocks reflectextreme temperature gradients, varying by several hundred degreesover a few metres or even centimetres and relatively short periods ofheating thatwith increasing temperature cause baking, annealing, andslagging. Mineral assemblages in the completely melted (slag) rocksare closely analogous to the products of crystallization of dry meltsof awide variety of compositions in laboratory quenching experimentsat atmospheric pressure. The two most common natural products offusion caused by combustion of organic material or gas are paralavaand clinker. Paralava is typically black to dark grey, aphanitic, vesi-cular, and has the appearance of artificial slag or ropy basaltic lava. Theterm clinker usually refers to burnt, unmelted, reddish rocks (brick-like), but theymay also be glassy as a result of extensive fusion (glassy

clinker) and therefore similar to buchite. Unlike paralava, however,clinkers do not show evidence of flow.

In this paper we describe the occurrence, geochemistry, miner-alogy (particularly low Ca-pyroxenes) and origin of melt rocks, para-lava of basaltic composition and clinker, that have been producedby combustion of coal seams near the Yellow River, Shanxi Province,North China.

2. Geological setting

In northern China, coal reserves occur over a vast region extending∼5000 km in an E–Wdirection and ∼750 km in a N–S direction acrossten provinces (from west to east; Xinijiang, Qinghai, Gansu,Neimongoi [Inner Mongolia], Ningxia, Shaanxi, Shanxi, Liaoning,Jilin, Heilongjiang). Coalfield and coal mine fires occur over thisentire area (Van Genderen and Guan, 1997) (Fig. 1a). The localitystudied is an upper Carboniferous–lower Permian bituminous coal-bearing sequence of mainly argillaceous sediments exposed on thebanks of the YellowRiver, western border of Shanxi Province,where atleast two coal seams have undergone combustion that is ongoingwithan along-strike burn rate of ∼7 m/year.

Lithos 113 (2009) 831–843

⁎ Corresponding author. Tel.: +82 2 3290 3172.E-mail address: [email protected] (R. Grapes).

0024-4937/$ – see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.lithos.2009.07.009

Contents lists available at ScienceDirect

Lithos

j ourna l homepage: www.e lsev ie r.com/ locate / l i thos


Fig. 1. a. Map showing distribution of coal fires across northern China (after Van Genderen and Guan 1997) and location of study area on the true left bank of the Yellow River, ShanxiProvince. b. Map showing geology of combustion metamorphism locality and sections shown in Figs. 3 and 4, Yellow River, Shanxi Province, China. The burnt rocks are located in theUpper Carboniferous Taiyuan and Lower Permian Shiqianfeng formations. Taiyuan Fm. (64–82 m). Upper: Dark grey, grey carbonaceous shale and oil shale. Middle to upper partscontain limestone/muddy limestone showing a northward facies change to a layer of sideritic nodules. Lower part is characterised by sandstone and 2–3 coal seams. Lower: Grey,dark grey shale, bauxitic shale, oil shale, intercalated with 1–3 layers of limestone. Middle to lower parts contain 2–4 layers of light grey sandstone with 3–5 coal seams, and alsosiderite, pyrite and ferruginous nodules. Shiqianfeng Fm. (46–52 m). Grey to dark grey shale, clayey shale, sandy shale and grey, light grey sandstone. Shale contains siderite nodules.

832 R. Grapes et al. / Lithos 113 (2009) 831–843


A geological sketch map of the area is shown in Fig. 1b and fieldrelations are illustrated in Fig. 2. Gently north-dipping metamor-phosed (burnt) rocks are well exposed in a cutting within the miningarea (Section 1; Figs. 1b, 2b) and in a roadside exposure along the trueleft bank of the Yellow River (Section 2; Figs. 1 b, 2c). Paralava andclinker that occur as fragments within the paralava, were collectedfrom a cross-cutting breccia body exposed in Section 2 (Fig. 2c,d) andform the basis of this study. The breccia is partly covered by fill and aretaining wall so that its extent and contact relations are obscured.The breccia has presumably resulted from an explosive combustionevent or events that may have been localised within a fractured areaof hot gas streaming above burning coal associated with extensivemelting followed by gravitational collapse into a cavity or cavitiescreated by the combusted coal. Similar collapse structures are alsorecorded as erosion-resistant breccia “chimneys” of paralava/clinker(Allen, 1874; Rogers, 1917; Sigsby, 1966; Cosca et al., 1989). It is clearfrom contact relations with rocks adjacent to the Yellow River brecciaoccurrence that the dark grey to black paralava has been highlymobile(low viscosity) in that it exhibits drip structures, flow textures aroundclinker clasts (Fig. 2d) and forms a film on virtually every crack andbedding plane of the adjacent brick-red clinker sequence (Fig. 2c)giving rise to a dark bluish grey-red mottling.

3. Analytical and recalculation methods

Paralavas and associated metamorphosed and fused sedimentaryrocks at the Yellow River locality were analysed by X-ray fluorescenceand analyses are listed in Table 1. In two samples (2; siltstone clinker)and (10; paralava), FeO was determined by titration and H2O mea-sured using a Leco RC-412 multiphase C/H/H2O analyser. Becauseof cm-scale variation of texture and mineralogy, particularly in para-lava (10), additional paralava “bulk” compositions (10a, 10b, 10c inTable 1) were obtained from EDS analyses of 1400×800 mm areasthat represent three distinct textural parts of the sample. As theparalavas contain only high temperature minerals (plagioclase, pyro-xenes, olivine, Ti-magnetite, apatite, ±cordierite) and glass they areinferred to have crystallized from a liquid. The fused clinker is alsoa largely crystallized from a liquid but contains a small amount(estimated at b5%) of unmelted detrital quartz, xenotime and zircon.

Estimates of bulk rock liquidus temperatures of paralavas andassociated clinker (2), and the sequence of equilibrium crystallization,mineral-liquid temperatures, etc., of a “basaltic” paralava composition(10a) were made using the MELTS programme of Ghiorso and Sack(1995) that is applicable to awide range of compositions frompotassic–mafic rocks to rhyolites, although best calibrated for basaltic liquid

Fig. 2. a. Actively burning hillside site and burnt rock talus near section 1, Yellow River. b. Section 1. Railway cutting exposure of burnt rocks above coal seams (now ash). The fusedsiltstone clinker (labelled melt rock) has a dark bluish-red colour and contains dark bluish-blackmelted siderite nodules and lenses (now largely magnetite–hematite). Joint surfacesin the clinker are lined with films of paralava. The uppermost part of the fused clinker immediately below pale grey coloured quartzite is orange-red and is baked rather than fused.The thickness of the upper burnt coal seam is about 40 cm. c. Roadside section exposed at locality 2, left bank of Yellow River, showing partly fused clinker (brick-red), carbonate–gypsum-rich layers (dark reddish-purple), a porcellanite layer (cream-white) and an outcrop of paralava with fragments of clinker (breccia chimney). d. Detail of paralava (bluish-black to black) containing fragments of fused siltstone clinker (brick-red). White arrow indicates location in c.

833R. Grapes et al. / Lithos 113 (2009) 831–843


compositions. Simulations were performed on the basis of NNO bufferconditions at 1 bar. It should be noted, however, that there is a sig-nificant difference in CaO and P2O5 between the analysed glass ofparalava (10a) and the “best-fit” MELTS residual glass composition(Supplementary Table 7). This is because apatite (or whitlockite) wasnot produced in the MELTS simulation. Except for slightly lower K2O(by ∼1.4 wt.%) in the MELTS glass, there is a good correlation with theanalysed glass composition, particularly the most abundant oxides,SiO2 and Al2O3. Application of MELTS is therefore considered appro-priate to demonstrate the crystallization path of this paralava com-position. MELTS liquidus temperatures for paralavas, clinker and glassare listed in Table 1 and Supplementary Table 7, respectively.

Minerals and glass in paralava (composition areas 10a,b,c) andclinker (analysis 2) within a single thin section (Fig. 3a) were analysedbyWDSusing a JEOLSuperprobe8800REMPat SunYat-sen (Zhongshan)University, Guangzhou (Canton), China, and a JEOL JXA-8600SC EMPatKorea University, Seoul, Korea. Operating conditions for both instru-ments were 15 kV accelerating voltage, beam current of 10-nA, beamdiameter of 2 μm for minerals and a beam diameter of 5 or 10 μmand reduced beam current of 5 nA for glass to minimize alkali vola-tilization. Well-characterised natural and synthetic mineral standardswere used. All analysis points were positioned using backscatteredelectron imaging (BEI). Mineral analyses are listed in SupplementaryTables 2–6 and glass analyses are listed in Supplementary Table 7.

Mineral (plagioclase, pyroxene, olivine)/liquid temperatures(where liquid=bulk rock composition, or derived from MELTS liquid

compositions in equilibrium with the crystallization of anorthite, lowCa-pyroxene, augite and olivine in paralava (10a)), were derived fromgeothermometers of Putirka (2008; Eq.24a for plagioclase/liquid;Eq.32d for clinopyroxene/liquid; Eq.28 for orthopyroxene/liquid;average of Eqs.21 and 22 for olivine/liquid). In addition, temperaturesof pyroxene crystallization in the paralavas were derived from thepyroxene thermometers of Lindsley (1983) and Lindsley and Ander-son (1983).

Recalculation of Fe2O3 and FeO in Fe–Ti oxide compositions, tem-perature and fO2 estimation, was made using the ILMAT excel work-sheet for ilmenite–magnetite geothermometry and geobarometry ofLepage (2003). This programme provides solutions based on a numberofmodels and for consistencyweuse themethodof Carmichael (1967)for calculation of Usp and Ilm components and the geothermobaro-meter of Spencer and Lindsley (1981) for calculation of T °C and fO2.

4. Lithologies and geochemistry

4.1. Paralava

The paralava is compositionally variable as shown by analyses ofthree bulk samples (9, 10 and 11 in Table 1). Centimetre-scale varia-tion of texture and mineralogy do exist, particularly in sample (10),and compositions are listed as (10a), (10b), and (10c) in Table 1.Analyses (9), (10a), (10b) have “igneous” compositions of low alkalibasalt–basaltic andesite and contain anorthite, low Ca-pyroxenes

Table 1Compositions of sediments, clinker and paralava, Yellow River.

Analysis no. Sediments and clinker Paralava

1 2 3 4 5 6 7 8 9 10 10a 10b 10c 11

SiO2 64.77 65.63 68.41 68.13 20.95 5.62 3.56 6.41 42.92 50.09 47.62 50.48 58.40 59.31TiO2 0.91 0.77 0.73 1.10 0.19 0.04 0.03 0.09 0.57 0.62 0.56 0.58 0.62 0.69Al2O3 23.84 21.37 21.06 25.54 5.50 3.52 2.34 2.43 15.21 17.28 18.14 19.91 20.47 19.08FeO (total iron) 3.31 4.62 3.51 0.63 58.26 9.95 82.51 81.33 20.53 11.77 14.05 10.98 7.11 9.68MnO 0.07 0.13 0.29 0.00 2.75 0.16 4.78 5.33 0.94 0.31 0.48 0.39 0.29 0.29MgO 1.23 1.44 1.23 0.57 7.97 7.11 3.32 0.81 4.76 5.20 6.40 5.73 3.10 2.35CaO 1.56 1.80 1.38 0.04 1.71 36.02 1.23 0.79 11.13 10.38 12.27 11.36 7.17 5.38Na2O 0.06 0.03 n.d. 0.05 n.d. n.d. n.d. n.d. 0.02 0.02 0.02 0.02 0.02 0.01K2O 2.14 2.26 2.29 1.83 0.06 0.03 n.d. 0.01 0.70 0.83 0.36 0.52 2.00 1.60P2O5 0.18 0.30 0.23 0.05 0.27 0.03 0.18 0.18 0.31 0.34 0.16 0.24 0.36 0.42LOI 1.61 0.64 0.51 1.12 0.72 29.38 0.27 0.32 0.18 0.70 0.51Total 99.68 98.99 99.64 99.06 98.38 91.86 98.22 97.70 97.27 96.85 100.06 100.21 99.54 99.32Fe2O3 (total iron) 3.68 5.14 3.91 0.70 64.75 11.16 91.70 90.39 22.82 13.08 15.61 12.20 7.90 10.76FeO 2.91 9.71Fe2O3 2.02 2.98MELTS liquidus (°C) 1109 1216 1148 1227 1219 1124 1145Paralava mineralsOlivine x xAnorthite x x x x x xAugite (x) (x)Pigeonite x x x xClinoenstatite/ferrosilite x x x xCordierite x xApatite x x x x xFe–Ti oxidea x x x x x

(x)=minor amount.1. Siltstone.2. Fused siltstone (clinker) [tridymite, mullite, cordierite, anorthite, Fe–Ti oxide, glass, relic quartz].3. Fused siltstone (clinker) [tridymite, mullite, cordierite, anorthite, Fe–Ti oxide, glass, relic quartz].4. Porcellanite (after kaolinite) [tridymite, cristobalite, mullite, pseudobrookite].5. Sideritic mudstone (with steaks and lenses of siderite).6. Annealed gypsum–aragonite–Ca–Al–Mg ferrite–(tridymite) rock. Sulphur not analysed.7. Fused sideritic mudstone (mainly magnetite).8. Fused sideritic mudstone (mainly magnette).9. Parabasalt.10. Parabasalt.10a, 10b, 10c — Different compositional parts of parabasalt 10; 10c — in contact with clinker (defocused beam EDS analyses of areas shown in Fig. 3c).11. Paralava.

a Ti-magnetite, ilmenite, rutile.



(pigeonite and probable clinoenstatite), ±rare augite, Fe–Ti oxides,±olivine, apatite and siliceous glass (Table 1). Fine-grained glomer-oporphyritic parabasalt (10a) has intruded coarse-grained porphyriticparabasalt (10b)(Fig. 3a,b). Other paralava compositions (10c) and

(11) are more siliceous and contain cordierite anorthite, clinoensta-tite/ferrosilite, Fe–Ti oxide, and minor apatite. These paralavacompositions are transitional to siltstone clinker that occurs asabundant inclusions in the paralava (Fig. 2d), as shown by increasing

Fig. 3. a. Photo showing part of the paralava–clinker thin section analysed delineating compositional areas of paralava (10a, 10b, 10c) and adjacent clinker. Rounded white areas arevesicles. b. Plane-polarised light microphotograph illustrating the grain size and pyroxene habits in the three compositional areas of the paralava. Section line A–B indicated in a.c. Backscattered electron image (BEI) photos of compositional areas (10a), (10b) and (10c) showing detail of habits and grain size of pyroxenes. Dark grey areas are anorthite andglass. Bright grains are Fe–Ti oxide. Bar scales=200 mm.



SiO2, TiO2, Al2O3, K2O and decreasing FeO, MnO, MgO, CaO andP2O5 towards the clinker contact (Fig. 4). The extremely low Na2O(b0.02 wt.%) in the paralavas can be attributed to sodium burn-out,along with volatile loss, during heating to fusion temperatures (e.g.Sokol et al., 1998; Sharygin et al., 1999).

4.2. Sedimentary rocks

Analysed sedimentary rocks (coal measures) associated with theparalava include siltstone, sideritic mudstone with lenses, streaksand nodules of siderite, porcellanite, and a gypsum–carbonate rock(Table 1). Based on XRD and optical identification, rock layers aboveburnt coal seams (now ash) have been baked and melted. Some silt-stone, particularly blocks that occur within paralava at Locality 2, hasalmost completely melted to form a glassy clinker containing cor-dierite, anorthite, mullite, tridymite, Fe–Ti oxide (analysis 2, Table 1).Relic quartz grains form nuclei of new tridymite. Cream-colouredporcellanite which appears to have originally been a kaolinite-richhorizon (Fig. 3b,c), is composed of tridymite–cristobalite, mullite andpseudobrookite. Siderite nodules (Fig. 3b) have decomposed tomagnetite–hematite (bulk compositions with 81–83 wt.% iron andhigh MnO of 4.8–5.3 wt.%; Analyses 7,8 in Table 1). Inferred sulphide-bearing ankerite-rich horizons (Fig. 3c) have been transformedthrough annealing and partial melting to a porous aggregate of mainlyCa–Al–Mg ferrites (brownmillerite–magnesioferrite series), and

minor cordierite, tridymite, K-rich glass (after “pelitic” component inthe rock). Abundant low-temperature gypsum and aragonite are alsopresent indicating that S andCO2weremobilized but not lost from theserocks during heating and cooling.

5. Mineralogy, textures and glass compositions

5.1. Paralava

5.1.1. PlagioclasePlagioclase typically forms euhedral tablets that often showmutual

growth interference. In all paralava compositions the plagioclase isunzoned with individual grain compositions of An100–96.2 and Orcontents between 0.7 and 1.8 mol% (Supplementary Table 2). Iron(as FeO) ranges between 0.39 and 2.28 wt.%. Formulae calculatedon the basis of 8(O) indicate that there is a close approach to the idealtotal of 5.000 cations per formula unit with totals b5.000 suggestingthe presence of an excess silica component (*Si4O8) of between 0.03and 2.8% (e.g. Longhi and Hays 1979; Beaty and Albee 1980).

5.1.2. PyroxenesThree pyroxenes, pigeonite, augite and clinoenstatite–ferrosilite

(see below) (nomenclature of Morimoto, 1988) occur in the paralavaand textural relations are shown in Figs. 3c and 5a,b. Pyroxeneanalyses, recalculated on the basis of 6 oxygens and 4 cations to

Fig. 4. Histogram plot of wt.% oxides in paralava compositional volumes (10a), (10b) and (10c) (Table 1) against thickness (mm) away from clinker (2) contact at 6 mm. Locationshown in Fig. 3a as A–B section line).



Fig. 5. BEI photos showing detail of textures in paralava. a. Compositional area (10a). Pale grey glomeroporphyritic Fe-pigeonite some with darker grey Mg-pigeonite cores,intergrown with anorthite. Interstitial darkest grey areas=glass. Bright grains=Fe–Ti oxide. b. Compositional area (10c). Skeletal clinoenstatite/ferrosilite (light grey) intergrownwith anorthite. Bright grains=Fe–Ti oxide; Cd=cordierite; darkest grey interstitial areas=glass. c. Compositional area (10a). Large, rounded olivine (light grey) with inclusions ofanorthite (dark grey) and Fe–Ti oxide (bright grains). The olivine is partly replaced by thin seams of orthopyroxene (?clinoenstatite). d. Compositional area (10a). Cluster of poikiliticolivine crystals (inclusions of anorthite and Fe–Ti oxide). Note the inclusion-free olivine growing inwards from vesicle. Light grey crystals intergrown with anorthite are pigeonite.



provide an estimate of Fe3+, are listed in Supplementary Table 3 andquadrilateral compositions are plotted in terms of atomic % Ca–Mg–(Fe2++Mn) in Fig. 6. The pyroxenes contain significant amounts ofMnO (0.41–1.64wt.%) and the sum of non-quadrilateral oxides rangesfrom 0.78–6.2 wt.% with Al2O3NTiO2NNa2O. Pyroxenes in (10c)with the lowest Wo-content (b2 mol%) have oblique extinctionwith γ:zc=∼15–20° and a small positive 2 V of b15° indicatingmonoclinic symmetry so that they are borderline clinoenstatite–ferrosilite. Grains with higherWo-contents that plot close to, or on theorthoenstatite–ferrosilite/clinoenstatite–ferrosilite–pigeonite bound-ary also have oblique extinction and could be pigeonite. In the absenceof XRD data we refer to pyroxeneswithWo b5mol% as clinoenstatite–ferrosilite (sensu lato). Clinoenstatite–ferrosilite has also been reportedfrom other paralavas/buchites derived from coal combustion (SenGupta, 1957; Hensen and Gray, 1979; Tulloch and Campbell, 1994).

In compositional area (10a) (Fig. 5a), augite (Ca42Mg40Fe18) occursas rare cores in pigeonite and larger pigeonite grains are zoned fromCa7Mg69Fe24–Ca11Mg42Fe48 (cores) toCa8Mg47Fe45–Ca8Mg40Fe52 (rims);smaller grains are homogeneous and have similar compositions torims of larger grains (Fig. 6). In compositional area (10b) (Fig. 3b), largepoikilitic pyroxene with between 1.67–4.4 wt.% CaO is present thatcontain inclusions of anorthite and sometimes Fe–Ti oxide (Fig. 3c).Spine-like extensions characterise grains in the transition to (10c).The poikilitic grains have cores of Ca5Mg70Fe26–Ca3Mg59Fe38 (clinoen-statite/pigeonite) and are rimmed by compositions of Ca4Mg49Fe47–Ca5Mg38Fe58 (clinoferrosilite/pigeonite). Compositional area (10c) (Fig. 3)is characterised by skeletal andplumose clinoenstatite–ferrosilitewiththe composition Ca2Mg50Fe48 (Figs. 4, 5b).

5.1.3. OlivineOlivine only occurs in compositional area (10a) and analyses are

given in Supplementary Table 4. Cation totals are N3.000 which sug-gests the possibility that some iron could be present as Fe3+ (e.g., Deeret al., 2001). Recalculation of the analyses on the basis of 4 oxygensand 3 cations yields between 0.037 and 0.129 Fe3+ and a small defi-ciency of Si thatmay indicate a substitution of the type 2Fe3+=Fe2++Si4+. The olivine containsmoderate amounts ofMnO (0.75–1.06wt.%),a feature also characteristic of olivine in parabasalt described from thesouthern Urals with between 0.60 and 2.1 wt.% MnO (Sharygin et al.,1999). Concentrations of CaO are low at between 0.17 and 0.96 wt.%.

Olivine mainly occurs as scattered sub-rounded poikilitic grainspartly replaced by orthopyroxene (Fig. 5c), as rare clusters of smallersubhedral–euhedral grains that contain abundant inclusions ofanorthite and some Fe–Ti oxide, and more rarely as inclusion-freerims partially lining gas cavities (Fig. 5d). Rare, small rounded homo-geneous grains of olivine enclosed in pigeonite are the most Mg-richat Fo54, whereas the larger grains may be weakly zoned from Fo42(core) to Fo38 (rim) (Fig. 6).

5.1.4. CordieriteCordierite is only found in the more siliceous sample (10c) and in

paralava (11) where it forms small homogeneous grains of XFe=0.36(Supplementary Table 5) in interstitial glass (Fig. 5b).

5.1.5. Fe–Ti oxidesAlthough magnetite occurs as homogeneous grains with ∼10–

16wt.% TiO2 in all compositional areas of paralava (10), themajority ofFe–Ti oxide grains are composite and consist ilmenite/hemo-ilmeniteand Ti-poor magnetite (3.5–6.3 wt.% TiO2) and hemo-ilmenite withirregular steaks of pseudobrookite (Supplementary Table 6). Ilmenite–hematitess compositions shown in Fig. 7 together with examples ofexsolution textures, plot above the solid solution tie-line reflectingtheir Al2O3 (2.4–5.0 wt.%), MgO (0.6–1.7 wt.%), MnO (0.1–0.9 wt.%)and CaO (0.1–0.4 wt.%) contents. Where analysed, V2O3 ranges from0.7–1.6 wt.% and Cr2O3 contents are b0.05 wt.% in all Ti–Fe oxides.

5.1.6. ApatiteApatite (or possibly whitlockite) occurs as needle-like crystals

within glass. Its fine-grain size precluded quantitative analysis.

5.1.7. GlassInterstitial glass is highly siliceous (78.2–83.3 wt.% SiO2), cor-

undum normative (2.7–5.2%), with K2O contents between 3.7 and5.2 wt.% and Na2Ob0.03 wt.% (Supplementary Table 7). No evidenceof liquid immiscibility, such as the coexistence of siliceous and basicglass, was found. The coexistence of acidic K–Al-glass and Fe-basicglass has been reported as a rare phenomenon in basaltic paralavaformed within burnt spoil-heaps, Chelyabinsk coal basin, Russia(Sharygin et al., 1999).

Fig. 6. Ca–Mg–(Fe2++Mn) plot of pyroxene compositions in paralavas 10a (filled circles), 10b (open circles), 10c (open squares) (Supplementary Table 3). Arrowed tie lines indicatecore–rim zoning. Grey-shaded areas=pyroxene stability fields at 1100 °C and ∼atmospheric pressure delineated by Lindsley (1983). Olivine compositions in (10a) are shown belowin terms of Fo–Fa content (Supplementary Table 4).



5.2. Clinker

5.2.1. PlagioclasePlagioclase compositions vary between An98.9–84.4 (Supplementary

Table 2). Some grains coexisting with tridymite (Fig. 8) have cationtotals significantly less than 5.000 indicating the presence of a *Si4O8

component of up to 3.7%. Potassium ranges between 0.13 and 0.39 wt.% giving Or values of 0.8–2.1 mol%.

5.2.2. CordieriteCordierite forms euhedral–subhedral crystals within glass and

commonly contains glass inclusions (Fig. 8). The grainsmay beweaklyzoned to more Fe-rich rims (Analyses 2a,b; Supplementary Table 4)and the overall compositional range of homogeneous and zoned crys-

tals is XFe=64–68. Potassium contents range between 0.18 and1.67 wt.% K2O.

5.2.3. Fe–Ti oxidesMost oxide grains were too small for quantitative analysis but rare

larger grains are composite and consist of TiO2-poor, Fe2O3-rich hemo-ilmenite and magnetite (Supplementary Table 6; Fig. 7).

5.2.4. Other phasesInferred tridymite occurs as needles and narrow-wedge-shaped

crystals within glass (Fig. 8). It also mantles grains of relic quartz. AnAl-silicate forms needle-like crystals in glass and clusters of needlessuggest replacement of primary muscovite grains in the fused silt-stone (Fig. 8a). The fine-grain size did not permit quantitative spot

Fig. 7. Compositions and textures of Fe–Ti oxides (Usp-Mtss, Ilm-Hemss and pseudobrookite (with single composite grain tie lines) in paralava and clinker plotted in terms of mole %TiO2–FeO–Fe2O3 (Supplementary Table 6). Filled and open circles=paralava; open square=clinker. BEI photos show exsolution textures of composite Fe–Ti oxide grains(compositions indicated by dashed arrowed lines) with darker grey parts=Ilm-Hemss or pseudobrookite and lighter grey parts=Usp-Mtss. Bar scale on all photos=10 mm. Lowerdiagram is a plot of log fO2 versus T °C for single grain oxide pairs (Supplementary Table 6). Oxygen buffer curves: MH=magnetite–hematite; NNO — nickel–nickel oxide;FMQ=fayalite–magnetite–quartz; WM=wüstite–magnetite.



analyses but a higher Al2O3/SiO2 ratio than expected for an Al2SiO5

composition indicates that the Al-silicate is probably mullite. Apatiteforms tiny needles within the glass. Occasional relic grains of xenotimeare present (Fig. 8a).

5.2.5. GlassGlass compositions are silica-rich (73.6–75.5 wt.% SiO2) with high

K2O content (5.2–7.6 wt.%) and have the composition of potassicrhyolite (Supplementary Table 7). Glass of similar composition is re-corded from other sedimentarymelt rocks resulting from combustion,e.g., Cosca et al. (1989).

6. Discussion

6.1. Temperatures of crystallization and phase relations

6.1.1. ParalavaLiquidus temperatures of paralava compositions range from 1227

to 1124 °C (Table 1) and textural evidence indicates that the sequenceof crystallization was anorthite, pyroxenes, Ti–Fe oxide±olivine,apatite. The MELTS cooling history of parabasalt (10a) shown in Fig. 9indicates initial crystallization temperatures of anorthite at 1225 °C,pigeonite (Ca9Mg65Fe26) at 1150 °C, augite (Ca41Mg36Fe23) at 1115 °C,

Ti-magnetite at 1105 °C, and olivine (Fo45) at 995 °C. These temper-atures are within the range of liquidus temperatures derived fromthermometric analysis of melt inclusions in early-formed anorthiteand clinopyroxene (1200–1300 °C) and mesostasis (1000 °C) in para-basalts from the Chelyninsk coal basin, Russia (Sharygin et al., 1999).

Although plagioclase crystallized over a considerable temperaturerange in the Yellow River parabasalts (Fig. 9) its composition in (10a)and the other paralava compositions, is restricted to An99–97 becausethe extremely lowNa2O (b0.02wt.%) precluded zoning. Textures indi-cate thatwith falling temperature anorthite crystals continued to growwith individual grains coalescing to form larger grains (e.g. Fig. 5b).The near liquidus temperature of anorthite crystallization in (10a) at1225 °C is slightly higher than the temperature of 1208 °C determinedfrom plagioclase–liquid thermometry (Supplementary Table 2).

In contrast to plagioclase, low Ca-pyroxenes and to a lesser extentolivine, are zoned. Pyroxene thermometry yields temperatures of 1150–982 °Cwith temperature differences between cores and rims implyingcooling intervals of 46 and 123 °C (Supplementary Table 3). The lowWo-content of all paralava compositions (5–11 mol%; where Wo=molar 3×[CaO−Al2O3+Na2O+K2O] in the Ol–Pl–Wo–Qtz system;Longhi and Pan, 1988) is consistent with the absence of augite exceptfor rare cores in pigeonite in (10a) that has the highest Wo-content.The augite core composition (analysis 3a; Supplementary Table 3)indicates a temperature of 1118–1120 °C and MELTS predicts augitecrystallization at ca. 1115 °C (Fig. 9). The XFe of basaltic liquids deter-mines whether pigeonite or orthopyroxene form (Longhi, 1991) andenlargement of the pigeonite stability field occurs with increasing XFe(e.g. Longhi and Bertka, 1996; Latypov et al., 2001). Basaltic paralavacompositions of XFeN0.55 (0.71 for 9; 0.56 for 10a) crystallize pigeo-nite and thosewith XFeb0.55 (0.52 for 10b) crystallize orthopyroxene(or clinoenstatite–ferrosilite in this case). This is in general agreementwith liquid boundaries on the plagioclase saturation surface in thesystem ol–pl–wo–silica where orthopyroxene is the only pyroxenecrystallizing from liquidswith XFe=0.30, pigeonite the only pyroxeneat XFe=0.75, andwith both pyroxenes forming at XFe=0.50 (Longhi,1991). However, the sequence of pyroxene crystallization in the basal-tic paralava compositions, i.e. Mg-pigeonite → augite→Fe-pigeonite(10a) and Mg-clinoenstatite/Mg-pigeonite→borderline clinoferrosi-lite/Fe-pigeonite (10b), is unlike that recorded in tholeiitic basalt andandesite, i.e. orthopyroxene+augite→pigeonite+augite (e.g. Naka-mura and Kushiro, 1970; Ishii, 1991). Except for Mg-pigeonite cores in(10a) that may be metastable, pyroxene core and rim compositions inthe paralavas plot within or define the limits of pyroxene stabilityfields at 1100 °C near atmospheric pressure (Lindsley, 1983) (Fig. 6).

Rare olivine of Fo54 that occurs in pigeonite in (10a) indicates anearly generation of olivine at ∼1176 °C (Supplementary Table 4) thatis not predicted by MELTS which indicates crystallization of olivine(Fo45) from a relatively siliceous liquid (∼69 wt.% SiO2) at ca. 995 °C(Fig. 9). Olivine–liquid geothermometry for porphyritic olivine ofFo42–38 in (10a) yields temperatures between 975and 965 °C (Supple-mentary Table 4). Incipient replacement of olivine by orthopyroxene(possibly clinoenstatite) (Fig. 5c) reflects a peritectic reaction.

The MELTS temperature of ca. 1105 °C for crystallization of Ti-magnetite is consistent with its occurrence as inclusions in olivine(Fig. 5c,d), and coincides with a sharp increase in liquid SiO2 as ex-pected (Fig. 9). The formation of Ti-magnetite also indicates relativelyhigh fO2, possibly approaching magnetite–hematite buffer conditions(Biggar, 1974). Subsolidus exsolution of hemo-ilmenite probablyoccurred under lower logfO2=−9.0 to −13.9 at temperatures of907–756 °C, with formation of pure ilmenite at lowest temperatures(536–567 °C) and logfO2=−24.9–21.9 (Supplementary Table 6;Fig. 7).

The high K2O and SiO2 of residual glass in the paralavas (Supple-mentary Table 7) implies that it had the potential to crystallize quartz/tridymite and K-feldspar. Tridymite as a late crystallizing phase hasbeen reported in some lunar basalts (Walker et al., 1972).

Fig. 8. BEI photos of clinker. a. Textural relationship between cordierite (Cd), anorthite(An) and tridymite (Td). Interstital pale grey areas are glass that contains needles ofprobable mullite (arrowed area). Small bright grains are Fe–Ti oxide. Qz=relic quartz.The large grain in top left corner is overgrown by tridymite; Xt=relic xenotime.b. Another area of the clinker showing needles of tridymite (dark grey) with cordierite(light grey) in glass with disseminated Fe–Ti oxide. Black areas in both photos are holes.



6.1.2. ClinkerFor the clinker (analysis 2; Table 1), the MELTS liquidus tempera-

ture is 1109 °C. This temperature is compatible with crystallizationtemperatures of 1087–1085 °C for anorthite (Supplementary Table 2)derived from plagioclase–liquid thermometry and temperaturesb1150 °C from phase relations in the anorthite–tridymite system(Longhi and Hays, 1979) implied by the maximum of 3.7%*Si4O8 inanorthite. The formation of tridymite together with probable mullitesuggests temperatures of at least 950 °C (Cameron, 1976) and pos-sibly as high as 1120 °C from the sillimanite=mullite+SiO2 reaction(Holm and Kleppa, 1966). With reference to the systems SiO2–Al2O3–

FeO (Schairer & Yagi, 1952) and SiO2–Al2O3–MgO (Keith and Schairer,1952), a cordierite, tridymite, mullite assemblage coexists betweenperitectics located at 1210 °C and 1443 °C, respectively. Assuming alinear change in temperature between Fe-cordierite (XFe=100) andMg-cordierite (XFe=0), cordierite compositions with XFe=63–68 inthe clinker imply crystallization temperatures of ∼1357–1368 °C.These temperatures are considerably higher than the clinker liquidustemperature of 1109 °C and would be expected to decrease (by ca.250 °C) in the presence of alkalis, particularly K2O in this case.

6.2. Cooling considerations

In the three paralava compositions, the marked difference in grainsize and crystal habit of pyroxenes in particular (Fig. 3b,c), can beattributed to differences in cooling rate and bulk composition. In com-positions (10a) and (10b), pyroxene core–rim thermometry impliesmaximumcooling intervals of∼140 °C,whereas in (10c), the pyroxeneis unzoned and crystallized at ca. 1038 °C (Supplementary Table 3).This temperature difference and the change in habit from zonedporphyritic clinoenstatite/pigeonite to clinoferrosilite/pigeonite in(10b) to unzoned skeletal/plumose clinoenstatite/ferrosilite in (10c)(Fig. 10) suggests the effect of a cooling frontmoving into the paralavafrom clinker xenoliths (Fig. 3b). Bulk composition is also an importantcontrol on textural development (e.g. Tsuchiyama et al., 1980) withthe more siliceous (and therefore viscous) composition of (10c) pro-moting development of skeletal/plumose growth habits of clinoen-statite/ferrosilite under conditions of relatively fast cooling. The finer-

grained glomerporphyritic texture of paralava (10a) compared with(10b) (Fig. 3b) probably implies more rapid cooling through a similartemperature interval of pyroxene crystallization that may have beenfacilitated by intrusion of (10a) into already cooled paralava (10b).

6.3. Paralava–clinker protoliths and other parabasalt occurrences

Sedimentary protoliths that melted to produce the paralava com-positions at the Yellow River locality can be evaluated by plottingvolatile-free recalculated bulk rock oxides SiO2, Al2O3, FeO [as totaliron], and MgO against CaO (Fig. 10). The plots indicate that the para-lavas can be accounted for by the melting of different combinations ofsiltstone, sideritic mudstone and ankerite-rich rock “end-member”components. The main source of SiO2, Al2O3 and K2O was siltstonewith CaO, MgO and FeO in the paralava suppled by ankerite andsiderite. In terms of SiO2, Al2O3 and FeO content, parabasalt com-positions (9), (10a) and (10b) indicate melting of ∼54, 64, 72% silt-stone+29, 13, 8% sideritic mudstone, +16, 23, 20% ankerite rock,respectively. The more siliceous paralava composition (10c) indicatesproportions of 83% siltstone, 8% sideritic mudstone and 9% ankeriterock consistentwith diffusion of Si, Al and K into amoremafic paralavafrom clinker (Fig. 4). For MgO, the protolith proportions are the samefor (9) as are the amounts of ankerite rock required to form all theother paralava compositions, but at fixed CaO the proportions of silt-stone (33, 40 and 70%) and sideritic mudstone (43, 38 and 22%) aresignificantly different with respect to compositions (10a), (10b) and(10c). This appears to reflect variable Mg in siderite as indicated by awide range of MgO (0.81, 3.32 and 7.97 wt.%) in the low Ca-sideriticmudstone analyses listed in Table 1.

With respect to themelting of ankerite and siderite, it can be notedthat with increasing temperature up to ∼1000 °C, ankerite breaksdown to form magnesioferrite+periclase+calcite, followed by Ca-ferrite+periclase, and finally decomposition of remaining calcite(Milodowski et al., 1989), but with rapid heating to higher tempera-tures, ankerite melts to form a low viscosity fluid (e.g. ten Brink et al.,1996). Siderite initially decomposes to Fe-oxide (magnetite or hema-tite depending on oxidation conditions) at∼420 °C, and at higher tem-perature of ∼560 °C for magnesian siderite (Patterson et al., 1991) but

Fig. 9. Plots of amounts of liquid and crystals (grams of phases/100) and liquid composition (wt.% oxide) versus temperature for MELTS equilibrium crystallization of paralava (10a).The temperature of first augite crystallization is indicated. The curves are extended to the average glass MELTS liquidus temperature that is assumed to be the quenchingtemperature of this paralava composition.



with rapid heating to temperatures of N1000 °C melting could occur,consistentwith a eutectic temperature of 1150 °C for carbonates in thesystem CaO–MgO–FeO (Nürnberg, 1981; Bryant et al., 1999). Clinkerfragments in the paralava are N95% fused siltstone.

Temperatures of coal combustion at the Yellow River locality areunknown, but must have been similar to or greater than the highestliquidus value of 1227 °C computed for paralava (10b). This value iswithin the highest temperature range of 1200–1400 °C determinedfor complete fusion of sandstone, shale and slag products of coalcombustion (Brady and Gregg, 1939; Whitworth, 1958; data quotedin Cosca et al., 1989).

Parabasalts have been described from other areas of combustionmetamorphism related to coal seams such as the Jharia coalfield, India(Sen Gupta, 1957), and as the result of fusion caused by burning gas inIraq (Basi and Jassim, 1974). The Jharia parabasalt forms isolatedbouldery masses within the coal field and consists of Ca-plagioclase,clinopyroxene, clinoenstatite, magnetite and glass. It is considered to

be derived by melting of “greywackish” sandstone containing Ca-plagioclase and ?chlorite. The Iraq parabasalt forms the cap rock of aline of six erosion remnants termed “burnt hills” developed along amajor reverse fault that provided escape channels for hydrocarbonsthat combusted. The parabasalt consists of Ca-plagioclase, clinopyr-oxene and glass and is considered to have been derived from thefusion of interbedded calcareous sandstone and marl.

Parabasalt as products of intensely burned waste heaps of theChelyabinsk coal basin, southern Urals, Russia, is also reported bySokol et al. (1998) and Sharygin et. al. (1999). The rocks are mainlyassemblages of anorthite, olivine, orthopyroxene, augite, pigeonite,Al-spinel, Ti-magnetite, pyrrhotite, glass (both mafic and acidic), andsome varieties also containminor kirschsteinite, leucite, K–Ba feldsparand apatite. Liquidus temperatures derived from thermometricanalysis of melt inclusions in early-formed anorthite and clinopyro-xene indicate temperatures of 1200–1300 °C. The source of theparabasalt melts was a finely crushed mixture of mudstone, clay–

Fig. 10. Plots of wt.% SiO2, Al2O3, FeO (as total iron), MgO versus CaO (volatile-free basis) for Yellow River combustion metamorphic rocks (numbered analyses listed in Table 1 andlabelled in the silica plot). Distorted triangles derived from each oxide plot have siltstone, sideritic mudstone and gypsum–carbonate ‘end members’ that allow estimation ofproportions of these fused protoliths for generation of paralavamelt compositions (filled circles numbered 9, 10, 10a. 10b. 10c and 11) and enclosed by grey-shaded ellipses. See text.



carbonate and siderite, similar to the proposed mixed protolith ofthe Yellow River parabasalt. In these basaltic paralavas also, the meltevolved to a K-rhyolite composition.

As a postscript it is interesting to note that the generation of para-basalt from sediment melting harks back to the idea of AbrahamGottlob Werner (1729–1817) that young surface basalt lava flowsdemonstrably associated with volcanic vents are the result of localisedmelting of rocks overlying burning coal seams (Hallam, 1989).

Acknowledgements

We appreciate the constructive reviews by Keith Putirka (Cali-fornia State University, Fresno, USA) and an anonymous referee thatresulted in a number of improvements to the manuscript. We wouldalso like to acknowledge the Natural Science Foundation of China(NSFC) for financial support (40672124).

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.lithos.2009.07.009.

References

Allen, J.A., 1874. Metamorphism produced by the burning of lignite beds in Dakotaand Montana territories. Boston Society of Natural History Proceedings, vol. 16,pp. 246–262.

Basi, M.A., Jassim, S.Z., 1974. Baked and fused Miocene sediments from Injana area,Hermin south, Iraq. Journal of the Geological Society of Iraq 7, 1–14.

Beaty, D.W., Albee, A.L., 1980. Silica solid solution and zoning in natural anorthite.American Mineralogist 65, 63–74.

Biggar, G.M., 1974. Phase equilibrium studies of the chilled margins of some layeredintrusions. Contributions to Mineralogy and Petrology 46, 159–167.

Brady, L.F., Gregg, J.W., 1939. Note on the temperature attained in a burning coal seam.American Journal of Science 237, 116–119.

Bryant, G., Bailey, C., Wu, H., McLennan, A., Stanmore, B., Wall, T., 1999. Iron in coal andslagging. The significance of the high temperature behaviour of siderite grainsduring combustion. In: Impact of Mineral Impurities in Solid Fuel Combustion.Gupta, R.,Wall, T., Baxter, L. (Eds.), Kluwer Academic/Plenum Publishers, New York,p.581–594.

Cameron,W.E., 1976. Coexisting sillimanite andmullite. GeologicalMagazine 6, 497–514.Carmichael, I.S.E., 1967. The iron–titanium oxides of salic volcanic rocks and their

associated ferromagnesian silicates. Contributions to Mineralogy and Petrology 14,36–64.

Cosca,M.A., Essene, E.J., Geissman, J.W., Simmons,W.B., Coates, D.A., 1989. Pyrometamor-phic rocks associatedwith naturally burned coal beds, Powder River Basin,Wyoming.American Mineralogist 74, 85–100.

Deer,W.A., Howie, R.A., Zussman, J., 2001. Rock FormingMinerals Vol. 1A:Orthosilicates.Geological Society of London.

Ghiorso, M.S., Sack, R.O., 1995. Chemical mass transfer in magmatic processes IV. Arevised and internally consistent thermodynamic model for the interpolation andextrapolation of liquid–solid equilibria in magmatic systems at elevated tempera-tures and pressures. Contributions to Mineralogy and Petrology 119, 197–212.

Grapes, R., 2006. Pyrometamorphism. Springer, Berlin, Heidelberg, New York. 276p.Hallam, A., 1989. Great Geological Controversies. Oxford University Press. 244pp.Hensen, B.J., Gray, D.R., 1979. Clinohypersthene and hypersthene from a coal fire buchite

near Ravensworth, N.S.W., Australia. American Mineralogist 64, 131–135.Holm, J.L., Kleppa, O.J., 1966. The thermodynamic properties of the aluminium silicates.

American Mineralogist 51, 1608–1622.

Ishii, T., 1991. Lava-flow and subvolcanic magma reservoir composition trends in theCa-poor pyroxenes of Hakone volcano, Japan. Journal of Petrology 32, 429–450.

Keith, M.L., Schairer, J.F., 1952. Stability field of sapphirine in the system MgO–Al2O3–

SiO2. Journal of Geology 60, 181–186.Latypov, R.M., Dubovskii,M.I., Alapieti, T.T., 2001.Graphical analysis of theorthopyroxene–

pigeonite–augite–plagioclase equilibrium at liquidus temperatures and low pressure.American Mineralogist 86, 547–554.

Lepage, L.D., 2003. ILMAT: an Excel worksheet for ilmenite–magnetite geothermometryand geobarometry. Computer & Geosciences 29, 673–678.

Lindsley, D.H., 1983. Pyroxene thermometry. American Mineralogist 68, 477–493.Lindsley, D.H., Anderson,D.J., 1983. A two-pyroxene thermometer. Journal of Geophysical

Research 88, A997-A906 (supplement).Longhi, J., 1991. Comparative liquidus equilibria of hypersthene-normative basalts at

low pressure. American Mineralogist 76, 785–800.Longhi, J., Bertka, C.M., 1996. Graphical analysis of pigeonite–augite liquidus equilibria.

American Mineralogist 81, 685–695.Longhi, J., Hays, J.F., 1979. Phase equilibria and solid solution along the join CaAl2SiO8–

SiO2. American Journal of Science 279, 876–890.Longhi, J., Pan, V., 1988. A reconnaissance study of phase boundaries in low-alkali basaltic

liquids. Journal of Petrology 29, 115–147.Milodowski, A.E., Goodman, B.A., Morgan, D.J., 1989. Mössbauer spectroscopic study

of the decomposition mechanism of ankerite in CO2 atmosphere. MineralogicalMagazine 53, 465–471.

Morimoto, N., 1988. Nomenclature of pyroxenes. Mineralogical Magazine 52, 535–550.Nakamura, Y., Kushiro, I., 1970. Compositional relations of coexisting orthopyroxene,

pigeonite and augite in a tholeiitic andesite from Hakone volcano. Contributions toMineralogy and Petrology 26, 265–275.

Nürnberg, K., 1981. Slag Atlas. Verlag Stahleisen, Germany.Patterson, J.H., Hurst, H.J., Levy, J.H., 1991. Relevance of carbonate minerals in the pro-

cessing of Australian Tertiary oil shales. Fuel 70, 1252–1259.Putirka, K., 2008. Thermometers and barometers for volcanic systems. In: Putirka, K.,

Tepley, F. (Eds.),Minerals, Inclusions andVolcanic Processes. Reviews inMineralogyand Geochemistry, vol. 69. Mineralogical Society of America, pp. 61–120.

Rogers, G.S., 1917. Baked shale and slag formed by the burning of coal beds. US GeologicalSurvey Professional Paper 108-A, 1–10.

Schairer, J.F., Yagi, K., 1952. The system FeO–Al2O3–SiO2. American Journal of ScienceBowen Vol. In, pp. 471–512.

Sen Gupta, S., 1957. Petrology of the para lavas of the eastern part of Jharia coal field.Quarterly Journal of the Geological, Mineralogical and Metallurgy Society of India29, 79–101.

Sharygin, V.V., Sokol, E.V., Nigmatulina, E.N., Lepezin, G.G., Kalugin, M., Frenkel, A.E.,1999. Mineralogy and petrography of technogenic parabasalts from the Chelya-binsk brown-coal basin. Russian Geology and Geophysics 40, 879–899.

Sigsby, R.J., 1966. The present general lack of “scoria” in two burning lignite areasin North Dakota. Annual Proceedings of the North Dakota Academy of Science,pp. 7–14.

Sokol, E., Volkova, N., Lepezin, G., 1998.Mineralogy of pyrometamorphic rocks associatedwith naturally burned coal-bearing spoil-heaps of the Chelyabinsk coal basin, Russia.European Journal of Mineralogy 10, 1003–1014.

Spencer, K.J., Lindsley, D.H., 1981. A solution model for coexisting iron–titanium oxides.American Mineralogist 66, 1189–1201.

ten Brink, H.M., Eenkhoorn, S., Weeda, M., 1996. The behaviour of coal mineral carbo-nates in a simulated coal flame. Fuel Processing Technology 47, 233–243.

Tsuchiyama, A., Ngahara, H., Kushiro, I., 1980. Experimental reproduction of textures ofchondrules. Earth and Planetary Science Letters 48, 155–165.

Tulloch, A.J., Campbell, J.K., 1994. Clinoenstatite-bearing buchites possibly from com-bustion of hydrocarbon gases in a major thrust zone: Glenroy Valley, New Zealand.Journal of Geology 101, 404–412.

Van Genderen, J.L., Guan, H.Y., 1997. Environmental monitoring of spontaneous com-bustion in the north China coalfields. Final report of European Commission. ISBN:90 6164 1527.

Walker, D., Longhi, J., Hays, J.F., 1972. Experimental petrology and origin of Fra Maurorocks and soil. Proceedings of Lunar Planetary Science, Conference 13th, pp. 797–817.

Whitworth, H.F., 1958. The occurrence of some fused sedimentary rocks at Ravens-worth, N.S.W. Journal of the Royal Society of New South Wales 92, 204–210.


Documents

Paralava and clinker products of coal combustion, Yellow River, Shanxi Province, China