Geological and Geotechnical Investigations of Chemakurthy Granites - A Case in StudySurendra.K and Venkat Reddy.DDepartment of Civil of EngineeringNational Institute of Technology Surathkal, srinivasanagar525025 Mangalore;Email: surendra.ce123@gmail.com, dvr1952@gmail.com;

AbstractWorld's rare and exclusive variety of Black Galaxy Granite occurs in Chemakurthy- Prakasam district Andhra Pradesh, India. Black Galaxy had a global demand in constructional and architectural engineering projects due to its glittery glaze, aesthetic values, style, splendour and sophistication to interior decors and designs. Generally all rocks available in the earths crust are not suitable for infrastructural engineering projects. In this paper selected rock deposits have been identified in Chemakurthy area for detailed quality assessment techniques. Geological, petrographical, geochemical and, geotechnical studied have been carried for selection of quality rock deposits. Bronzite gabbro in infrastructural constructional and architectural designs is being utilized .In stone trade industry these rocks are utilized on the name of Chemakurthy granites. Bronzite gabbro is one of the unique stone it possess orange, yellow foliated minerals. Processing, polishing of these rocks enhances its colour, texture overall its appearance. Macro and micro -discontinuities rock deposits make valuable deposits worthless. Inherent geological discontinuities in rock deposits lead to huge wastage of resources, not suitable for any engineering purpose. Geo-technical studies also carried out for selective rocks to establish their strength characters and durability. Geological and geotechnical studies have revealed to demarcate defective and, defective free rocks deposits prior to utilizationKeywords: Andhra Pradesh, Bronzite gabbro, Black galaxy granite, Chemakurthy Granites construction projects, and Geological and Geo-technical characteristics..

National Conference on Technological Innovations for Sustainable infrastructure: 13, 14 March-2015

TISI-2015, National institute of Technology Calicut1. IntroductionIn the field of Dimensional stone industry, India occupies an eminent position of possessing unique varieties. Andhra Pradesh contributes nearly 20 varieties of DSG. The popular known variety Galaxy Granite is from Chemakurthy village located 25 kms from Ongole in Prakasam district .Prakasam district has come into prominence as a granite producing district in the State in recent years, after discovery of "Galaxy Granite" in the Chemakurthy area of the District; this unique type won international recognition. This variety is being quarried around Chemakurthy and R.L.Puram whereas the black gabboric-pyroxenite is being quarried near Budavadaa special rock type characterized by rare mineral assemblage, belonging to lower Precambrian era as per the geological time scale. The rocks in this area are composed of mixture of mafic and felsic minerals, predominantly pyroxene and plagioclase feldspars .The pyroxenes are dominated by laminated flakes of specific orientation exhibiting bronzite like metalloidalluster or schiller on chief cleavage face and is designated as Bronzite. The Bronzite mineral present in the rock is of high commercial value by virtue of its twinkling effect, presumably due to schillerization on planar surface, especially when the rock is cut and polish parallel to the foliation .It is because of the twinkling effect .It has attained the commercial name Galaxy resembling the twinkling crystals namely gold spots are the special attraction to this mafic rock (PandurangaRao.&Deva Pratap,&Govinda Raj1996). The unique properties of Black Galaxy granite that makes them look like the mirror image of a far away galaxy, is what gives it its name as black galaxy granite.As the black galaxy granite occurrence of the Prakasam district have gained multinational importance, the present study focuses on geological significance of black galaxy granite deposits of Chemakurthy, various structural characteristics, inherent defects, present in the stone deposit. Petrography and mineralogical composition and geotechnical properties are analysed. Granite quarries and polishing units of Andhra Pradesh is shown in fig1.

Fig.1 Granite quarries and polishing units of Andhra Pradesh

2. Chemakurthy igneous complex:

The Chemakurthy Igneous Complex is considered as Massive Concentric Type intrusive magmatic body. It is exclusively restricted to the outermost rim of a concentric body of Igneous Complex covering an area of approximately 30 Sq.marea. The individual rim of the concentric igneous body represents a particular type of igneous rock, which is the manifestation of in-situ crystallisation, fractionation and differentiation of basaltic magma both in time and space. The core of the igneous complex is constituted by highly coarse grained variety of rock; represented by pryroxenite / anorthosite which gradually changes to clino-pyroxene gabbro to finally bronzite gabbro (Galaxy granite) as the outermost rim. It is bronzite gabbro.Important constituent minerals are pyroxene represented both by clino- and ortho- pyroxene; and feldspar represented by a Ca-rich plagioclase members around labradorite. It is a Bronzite bearing gabbro. District resource map of Prakasam district is shown in fig2.

Fig.2- District resource map of Prakasam district

3. Geological setting:

The study area is a part of bronzite gabbro ring falling in the peripheral zone of this outer rim of bronzite gabbro is one of the constituent of Chemakurthy Igneous Complex which is emplaced into the older biotitic-hornblende schist as evidenced in the area, further south and south-east. The field investigations carried by at Chemakurthy and the geological maps produced by Geological Survey of India (1988) shown that outer rim is acidic and second rim is gabbro. This oval-shaped body is 15 Km long (N-S), 4-7 Km wide (E-W) and occupies 35 Sq.m area. It is constituted by an outer rim of bronzite rich gabbro (galaxy granite) followed by an highly elevated crecentic shaped ridge of clino-pyroxene gabbro, which is further followed by central core of olivinpyroxinite and massive anorthosite i.e. central part of the body and its core is composed of olivine Pyroxinite and anorthosite, followed by clino-pyroxene gabbro and lastly by bronzite rich gabbro. The galaxy granite, therefore, forms the outer most rime of this concentric body. The bronzite gabbro has been accomplished by insitu fractional crystallization, in the wake of differentiation from single magmatic body. With conversion of enstatite (OPX) into bronzite, due to excess availability of iron under oxygen deficient conditions.

The concentration of bronzite gradually increases from the central parts of the igneous complex to outer gabbroic rim. Within the bronzite gabbroic rim, the abundance and size of the bronzite increases towards peripheral area. The bronzite is a variety of orthopyroxenes i.e Enstatite, (containing more than 50 % Fe closer to Mg end (DHZ)) which is bronze like with pearly metallic luster. Poldervaart (1947) has carried experimental studies on orthopyroxenes and concluded that the bronzite is an intermediate between enstatite and hypersthene and assigned the status of an independent specie by itself and can be distinguished by pleochroism .The trend of lineation in bronzite gabbro from the field evidence suggest that it varies from N 350 E (central area) to N 700 E (east and west limbs). Indicating its syn-emplacement / crystallization deformation. The fracture pattern in the working quarries suggests that the deposit has suffered post emplacement deformation.

4. Geological investigations-field observations.

Geology of rock deposit is one of the most prominent factors in assessment of quality, quantity, exploration, exploitation and economy of exploration. Geological aspects such as topography/terrain conditions/geomorphology, stratigraphic position, mineral composition, textural variation, weathering and alteration , colour variation, structural conditions like macro and micro discontinuities ,intrusive veins etc. plays significant role in economic exploitation of rock deposits like granite mining. Careful studying favourable and unfavourable structural features in mining activity is useful to cut down the production cost and improving the quality of the product both in mining as well as in processing sector. The favourable geological structures in rock deposits are sheet joints, vertical joints, steep dipping foliation planes, magmatic structures etc. Unfavourable geological structures like close spaced vertical/oblique joints, minor faults, hair line fractures etc. in a granite mining adversely effects of quarrying operations to getting bigger size blocks (kaniska, 2005). Sheet joints present in the commercial rock deposit minimizes the development of high cost quarry equipment for bottom cutting. In most of quarries where vertical and sheet joint persist, the joints facilitated easy and smooth splitting of rock deposit, minimum waste ,high recovery and low cost of production.(kaniska,2004).Field investigations revealed that due to presence of unfavourable structures, getting low rate recovery i.e. 3% to 12%.Due to presence of unfavourable structures, mining entrepreneurs getting loss of money, not getting bigger size blocks and getting low rate of recovery.Detection of defects in dimensional stone industry plays a significant role in quality assessment. Natural defects stone industry adversely affects the quality and quantity of rock blocks. Macro defects like colour variation, texture variation. Structural discontinuities, inclusions, intrusions and contact zones etc. are can be identified by careful visual examination of stone deposits. Micro fractures, stress minerals, alterations of minerals are can be identified by systematic micro Petrographic analysis of entire stone deposits.

4.1 Field observations:

Field identification of defect of stone deposits prominent part quality assessment. Following are some field observations and defects are found out while visiting the granite quarry. Beauty of stone dependence upon the colour index Gabbro norite shows considerable variation in colour both laterally and downwards. Rock sample are suffers from uneven and erratic distribution and large variation in size and shape bronzite grain besides presence of numerous defects like black and white lines etc. galaxy granite occurs under a overburden comprises 3 to 6 m, over burden comprises 0.5m to 1.5m thick soil surface followed by weathered bronzite gabbro .weathered zones contains exfoliated boulders formed due to spheroid weathering.Feasible development of foliation is observed in bronzite gabbro. Foliation trend varies from N250E-S250W to N700W-S700E.Joints, shear zones, a few minor faults and lineations were recorded in investigated area. Two sets of prominent joints trending in N100E-S100W and N750W-S750E directions are present in the investigated area. Both joints are vertical and open, spacing varies from 0.5m to 1.5m.hairline fractures and cracks found on top layer not extending beyond 0.5m depth. Large crystals of bronzite, white hairlines, white and black lines, flowers, closely spaced joints and erotic distribution of bronzite are noticed. Study of the quarries from the point of geology and structure, nature and frequency of defects, rock mass grade, recovery and size of blocks produced reveals that RMG is about 50% and recovery varies from 8 to 20%.photograph showing defects in stone deposit. Structural defects in Chemakurthi quarry is presented in fig3.

Fig3 Structural defects in Chemakurthi quarry.

5. Petrography

Petrographic analysis of litho units gives invaluable data on their sawing and polishing capabilities. Petrographic characters grain size, degree of uralitisation of pyroxenes, sasuritisation of plagioclase feldspars, cloudiness in feldspars, presence of opaque ores, presence of free quartz and micro pegmatite common in commercial granite. These decide nature and quality of granite deposit. (Kaniska 1995&jayabalan 2005).Bronzite gabbro is a melanocratic, compact, and granular rock. With impregnations of bronzite an orange- yellow fallacious mineral with pearly metallic lustre. The other important minerals are Ca-plagioclase and pyroxene. The minerals present have an average hardness of 6.0 (Mohs Scale). Bronzite occurs with varied orientation. 5.1 Microscopic Features:

Detailed microscopic studies reveal that the grain size of both pyroxene and feldspar is varying and range from 100 to 800 microns. Under microscope the orthopyroxenes (bronzite) can be distinguished from clinopyroxenes (augite) by virtue of extinction angle often the exsolved iron-oxide occupy cleavage planes of clino-pyroxene. the bronzite show straight extinction and the augite show oblique extinction. Further, the bronzite show pleochroism and one set of cleavage where augite show two sets of cleavage with large extinction angle. The plagioclase occurs as lath shaped grains with lamellar twinning. Often the lamellae show bend-structure indicating that they have suffered deep seated deformation. The ophitic / sub-ophitic texture reveals that the plagioclases are the earliest formed mineral enclosing pyroxenes.The interlocking granular texture exhibits the discrete and isolated grain of bronzite in plagioclase (labrodorite) feldspar. The secondary minerals viz. iron oxides, biotite, quartz were formed by the alteration of mafic minerals and feldspar and occur as micro granular grains within the interstitial spaces. It is possible that Biotite and iron oxides could contribute dark black tone of the polished rock. Micro granular Quartz occurs as interstitial grains with clouded plagioclase . optical microscopic of gabbro are shown in Fig 4 and 5.

Fig.4 Optical image of gabbro

Fig.5 Optical image of Hypersthene-augite with quartz

Four samples are tested for Petrographic analysis using optical microscope. Out four samples two sample results tabulated table no 1.

Table no.1 Petrographic analyse table:

Mineral Sample-1Sample-2

Opx(hypersthene.brozite)45%35%

Cpx(augite)15%15%

plagioclase38%55%

magnetite-

biotite-3%

apatite-2%

Petrological studies reveal that the rock is medium grained and composed essentially of hypersthene, augite, and plagioclase feldspar with minor amounts of biotite, apatite and opaque. Absence of quartz in modal composition makes rock soft and well suited for utilities and polishing industry.

6. Geo-chemistry:Geochemical parameter is more essential to evaluate characteristics of the granite deposits. The colour of the deposit is controlled by the proportions of major oxides and trace elements. Presence of iron imparts shades of pink, yellow, green, and even black presence of barium and chromium imparts greenish colour. Black galaxy granite in study area is an olivine gabbro norite.The microfabric and mineralogical aspects of the was studied using Scanning Electron Microscope (SEM).The scanning electron microscope used in present study is of the type JEOL JSM6380 LA.. Colleted Major element analysis of gabbro samples is presented in the table no 2.Table no 2: Major element concentration of gabbro:

s.noconstituentsample1sample2

1Sio247.7848.92

2Tio200.120.22

3Al2o320.9120.05

4Fe2o31.841.49

5Feo7.656.08

6Mno0.090.12

7Mgo9.158.16

8Cao9.5212.32

9Na2o2.652.21

10K2o0.170.13

11P2o50.080.11

Sio2shows variations from 47.78% to 48.92%.in study area rock deposits Al2o3varies from 20.02 to 20.05%.SiO2, Na2O, K2O shows somewhat similar characteristics in their distribution, whereas the other oxides like MgO, MnO, CaO, TiO2 makes as one cluster of similar attitude in their behavior. From the major element analysis, it is observed not contain that rock deposits does not contain any deleterious substance. Scanning electronic image of black galaxy granite shown in fig.6. Mineral composition of Black Galaxy Granite sample shown in fig 7.Fig.6 scanning electron microscopic image of black galaxy granite.

Fig.7 Mineral composition of Black Galaxy Granite sample

Mineral composition of Black Galaxy Granite by conducting SEM with edx tabulated in table no.3

Table no 3: Percentage Mineral composition of Black Galaxy Granite sample

7. Geotechnical investigations:

Dimensional and ornamental stones for engineering applications have to satisfy not aesthetic needs but also technical characteristics. Unfortunately in India dimensional stone are yet to realize importance of technical characterization of stone deposits. Physical strength properties of rock is very important for optimal use of stones as a structural material. Geotechnical characteristics of dimensional stones are helpful various stages of assessment Exploitation and marketing. Geotechnical characters not only help in entrepreneurs to compute in the world market, but also in their preservation. Some of the rock mechanical properties studied & test type and applications tabulated table no.3.

Table no 3: Rock properties, test type and their applications:

s.nopropertiesTest typeApplications

1colourVisual and microscopicobservation

To establish technical name of the rock, to identify micro-fracture.

2Mineral composition

3Texture and grain size

4Density and specific gravityLaboratory method (IS 1122-1974)To determine the weight of rock for hand-ling

5Porosity and water adsorptionLaboratory method (IS 1124-1974)To determine the degree of decomposition rock

6Ultrasonic pulse wave velocityUltrasonic Non- Destructive digital testerUseful to de-termine sound-ness of the block

7HardnessSchmidt Impact HammerUseful to assess quality of mineral constituents

8DurabilitySlake dura-bility test (IS 10050-1981) Essential for assessing grani-tes used in the chemical indu-Stries & labs.

9Protodykonov strength indexProtodyakn-ov apparatus To find compressive strength by indirect method

10Point load indexPoint load strength test(IS 8764-1998)

11Unconfined compressive strengthCompression test(IS 9143-1979)Useful to rock suitable for engineering purpose

12Tensile strengthBrazilian test(IS10082-1981)Useful in cal-culating thick-ness of slab.

7.2 Various rock mechanical properties:Stone used for dimensional stone not only have aesthetics appearance but also it should structural suitable for to resist load acting on it. Some rock mechanical properties like density, strength tests, non-destructive tests etc. and their significance presented below.

7.2.1 Density:

Rocks have a wide range of density, which depends upon mineral constituents and degree of compactness in addition to the depth at which it exists. IS: 1122-1974 describes the procedure for determining the density of the specimen. Tests are conducted on sample prepared form bulk sample as prescribed by Indian standards. It is found that density of granite in study area varied from 2.9 to 2.94 gm/cc.

7.2.2 Natural Moisture Content:

ISRM (Part I) has suggested procedure for determining the moisture content in the laboratory. Excess moisture content gives an indication that rock sample is more porous, making it as lesser strength. With increase in moisture content, bearing capacity of rock generally decreases. Moisture content of test samples varies from 0.006 to 0.008%.

7.2.3 Porosity and Water Absorption:

Porosity describes how densely the material is packed in a rock.Porosity depends upon the shape of mineral grain sizes, degree of compactness and cementation. Absorption Value is capacity of a stone to absorb moisture when immersed in water for 72 hours or till saturation. IS: 1124-1974 describes the procedure for determining the porosity and water absorption of rock specimens. Study area laboratory results reveal that porosity varies from 0.3 to 0.4 %. And water adsorption varies from 0.03 to 0.11%.

7.2.4 Ultrasonic Pulse wave velocity test:

The Ultrasonic pulse velocity test is a dynamic method of rock testing in the laboratory. Measurements of wave are often done by using P wave and sometimes, S waves. P-wave velocity measures the travel speed of longitudinal (primary) wave in the material. ISRM suggested the method of conducting the ultrasonic pulse test using ultrasonic concrete tester. By noting the time required for pulse to traverse through the length l of the specimen, the pulse velocity V of wave is calculated. The pulse velocity is useful to assess the soundness of the block and selecting suitable explosive splitting technique. A well compacted rock has generally high velocity as the grains are all in good contact and wave are travelling through the solid. For a poorly compact rock material, the grains are not in good contact, so the wave will partially travel through void (air or water) and the velocity will be reduced. The pulse velocity in the rock depends on its density and its elastic properties which in turn are related to the quality and the compressive strength of the rock. The test is based on the pulse velocity method to provide information on the uniformity of rocks, cavities, cracks and defects present in rock sample. The ultra sonic pulse wave velocity of granite varies from 4100 (m/sec) to 5682 (m/sec).

7.2.5 Rebound Hardness test:

Hardness is resistance of a stone to rubbing and grinding action under the wheel of the traffic as also due to mutual attrition. If the rock is not sufficiently resistant to this type of action, it may wear out at a rapid rate causing losses in terms of time and money. ISRM-Part 2 suggests the method to determine the hardness number of the rock. Schmidt Hammer is used for the test. But in the present investigation, electronically controlled, digitized instrument (DIGI Schmidt 2000, Betonoprufer concrete tester) used. .This property is useful to assess the type and quality of various mineral constituents of the stone and the bond strength that exists between mineral grains. Rebound hardness no tested rock sample varies from 60 to 75.

7.2.6Unconfined Compressive Strength:

Compressive strength is tendency of rock fails by compressible forces. The value is termed unconfined or Uniaxial because the test specimen (cylinders of length-diameter ratio 2-2.5) has no lateral support or restraint and is being compressed only along one axis .the factors affecting are mineralogy, grain size and porosity, the external properties that effect the test results are friction between patterns and rock surface, specimen geometry like shape, length to diameter ratio, rate of loading and environment under which loading done. the cubes are dressed to standard size as per IS:9143-1979 to conduct compression test on rock samples. From laboratory tests, found that the compressive strength of selected rock samples varies from 113.21 to 137.16 m.pa.

7.2.7 Tensile Strength:

The low tensile strength is due to the existence of micro-cracks in the rock. The existence of micro-cracks may also be the cause of rock failing suddenly in tension with a small strain . The knowledge about tensile strength of rocks is important in analyzing the rock strength and stability. An average tensile strength of the rock has been found to be one-twelfth of its compressive strength. In the present investigation, determination of tensile strength is made by Brazilian test. ISRM Part 2 and IS: 10082-1981 gives detailed description and scope of the test.in the laboratory tests, rock specimens are obtained from the rock of the block drilled in one direction. the specimen diameter approximately 54mm and thickness should be approximately equal to specimen radius. Tensile strength of rock samples are varied from 11.8 m.pa to 133 m.pa.

7.2.8 Durability:

Nothing is everlasting, stones included. But the rate at which a stone deteriorates under the attack of natural processes (i.e. it weathers) varies from rock to rock. Durability or resistance to weathering is determined by the composition and texture of a stone on the one hand and also the environment where it is ultimately used in construction on the other hand. Their durability means their capacity to withstand the imposed loads without undergoing any deterioration. Durability of study area rocks were determined by Slake durability tests. IS: 10050-1981has suggested standard method for determining the slake durability index. This test is used to assess the resistance offered by a rock sample to weathering and disintegration, when subjected to two standard cycles of wetting and drying in a slaking fluid. Slaking fluid is the fluid used while conducting slake durability test. It may be tap water, corrosive ground water or any other liquid. Usually, tap water at 200C is specified for the test. Based laboratory tests Slake durability is very high.

7.2.9 Point load Strength Index:

The point load test involves the compressing of a rock sample between conical steel plates until failure occurs. The apparatus for this test consists of a rigid frame, two point load platens. a hydraulically activated ram with pressure gauge and a device for measuring the distance between the loading points IS: 8764-1998 has established the basic procedures for testing and calculation of the point load strength index. There are three basic types of point load tests axial, diametric, and block or lump. In present investigation, point load strength index is calculated by using irregular shape sample or lump. Point load strength index varies from 7.5 to 8.9.

7.2.10Protodyaknov Strength Index (Ps):

The Protodykonov strength scale finds wide use in Russia, Poland and other East European countries. This scale assigns a series of numbers for rocks in ascending order of strength. For rocks the number ranges from 1 to 20.Here sample in the form of lumps are taken from insitu rocks. Each sample is broken up with a hammer and 5 tests specimen consisting of fragments of 20mm to 40mm in size and of each 10 to 20 cm3 are picked. Each test specimen is placed in a cylinder of 76 mm internal diameter and is pounded with a 2.4 kg drop mass falling through a distance of 0.6 m. the number of impacts 'n' to which these tests specimen are subjected 5 to 15 depending upon the strength of the rocks. After pounding all five specimens, the test materials are sieved on a 500micron screen. Fines which pass through 500 micron screen arc poured in to the tube of volumnometer is recorded. Protodykonov proposed Classification of rocks based strength index. Protodykonov index varies from 11 to 13.

7.2.10.1 Classification of rocks (After Prof.Protodyakonov):

Prof.Protodyakonov proposed classification of rocks based on Protodykonov index. The classification tabulated in the table no 4.Table no .4 Classification of rocks based on Prof.Protodyakonov)

CategoryDegree of hardnessRockProto-dyakonovindex

1Extreme hardBasalt20

2Very hardHard granite15

3hardGranite8

4Rather hardSand stone6

5Medium hardHard clay shale4

6Medium hardVarious shale

7Rather softSoft shale2

8Rather softRock debris1.5

9Soft caly1

7.3 Results of geotechnical tests:

Physical properties of the granitic rocks were determined by a variety of laboratory tests. The specimens were prepared and tested in accordance with procedures given in IS-codes and I.S.R.M standards. Four samples are taken for test. Average of four samples is taken as result of test. The results of tests are tabulated in table no 5. Results of tests are compared with Indian standard for structural granites (IS 3316-1974) & specifications for polished building stones granite (IS 14423(part 1)-1995 ;( Reaffirmed 2012).

Table no.5 Results and comparison of geotechnical properties with standards.

S.nopropertyIS-14223Test Resultcomment

1Moisture content (%)0.15(max)0.008Less natural moisture content

2Dry density(N/mm2)2.25 to 2.682.91Fairly suitable.

3Specific gravity2.752.96Suitable for structural purpose

4Water adsorption0.500.11Lees water adsorption

5porosity1 to 20.33Less porous

6Compressive strength kg/cm21300-22001215Suitable.

7Tensile strength kg/cm290(min)125Suitable.

8Hardness (Schmidt no)85-11070.8Value less than code specifications.

9Ultra sonic pulse wave velocity m/sec50005197Suitable for structural purpose

10Point load Strength Index8.35Suitable for structural purpose

11Protodykonov Strength IndexProtodykonov index12.07Hard to very hard rock

12Slake durability testBased on IS1005097.2Extremely high

Geotechnical parameters which determined are conforming to specifications for use in dimensional stone industry. Rock sample tested are conform to specifications for structural granite (IS 3316-1974) i.e that compressive strength shall not less than 1000 k.g/cm2 , true specific shall not less than 2.6 and water adsorption shall not be more than 0.5%. Finally geotechnical investigations found that black galaxy granites are suitable for use in civil engineering projects as decorative stone.

Conclusions:

1. Chemakurthy bronzite gabbro is one of the unique dimensional stones being utilizing in architectural and civil engineering projects as exterior and interior decorative stones. Black Galaxy is a global favourite because of its glittery glaze that lends aesthetic values, style, splendour and sophistication to interior decors and designs. And being the only producer and exporter of Black Galaxy, Chemakurthy is raking in the moollah.2. Geological studies very helpful in assessment of quality, quantity, exploration, exploitation and economic value ability. Geological studies reveal that rock deposits of Chemakurthy black galaxy shows considerable variation in quality and quantity both in laterally and downwards. Erratic distribution of Bronzite, presence of numerous defects like black and white hair lines, small shear zones, minor fractures, joints, lineaments, few hair line fractures etc. are the defects noticed in study area.3. Due to presence of some defects , black galaxy granite quarries suffering low rate of recovery from 5 to 15 %. Some rock deposits in Chemakurthi, showing variations in colour texture and structural defects .These rocks are not suitable for infrastructural engineering or constructional engineering projects. and such type of stones causing waste material acclamation.

4. Petrographic analysis of stone deposits gives invaluable data on their sawing and polishing capabilities. Petrological studies of selected black galaxy granite samples shows that rock is medium grained and composed of hypersthene, augite and plagioclase feldspar with minor amounts of biotite, apatite and opaques. 5. Geochemical essential because the colours of stone deposit controlled by proportions of major and trace elements. From major element analysis (chemistry) , observed that selected black galaxy stone samples does not any deleterious substance which imparts its suitability in dimensional stone granite industry,6. Physical strength properties of rock are very important for optimal use of stones as structural material. Geotechnical parameters (Density, Sp.Gr, Hardness, porosity, Adsorption, compressive and tensile strength, slake durability etc.) determined are conform to specifications for use in constructional engineering projects and stone industry.7. Rock engineering properties of Chemakurthi rock deposits shows that they are most suitable for engineering design. Most of the rocks tested are shown their usage for applications as structural material. However highly fractures and dislocated rock deposits are not shown the required engineering properties. These rocks are rejected in civil engineering works due to due to their varied engineering properties and structural in ability to resist loads.8. Quality assessment techniques such as geological, Petrographic, geochemical, geo- technical very helpful in improving its quality, quantity and marketability.References [1] Bhattacharya, S. (1980): Petrography of the anorthosite-gabbro-pyroxenite Complex ofChimakurti, Prakasam district, Andhra Pradesh. Rec. GSI. Vol. 113.pt.5.pp 68-71.[2]Bieniawski Z. T., Estimating the Strength of Rock Materials, Journal of South African Institute of Mining and Metallurgy, March, 1974.[3] Chary K.B., Sarma L.P., Prasanna Lakshmi K. J, Vijayakumar N.A, Naga Lakshmi V., and Rao M.V.M.S., Evaluation of Engineering Properties of Rock Using Ultrasonic Pulse Velocity and Uniaxial Compressive Strength, Proceedings of National Seminar on Non-Destructive Evaluation Dec. 7 - 9, 2006, Hyderabad, 2006.[4] Engin C. Koncagu l, Paul M. Santi, Predicting the unconfined compressive strength of the Breathittshale using slake durability, Shore hardness and rock structural properties ,International Journal of Rock Mechanics and Mining Sciences vol.36.no.2 page no. 139-153 .1999.[5] J. Nagaraju, T.R.K. Chetty, Imprints of tectonics and magmatism in the south eastern part of the Indian shield: satellite image interpretation, J. Ind. Geophys. Union,v.18, no.2, pp:165-182,April 2014.[6] Lianyang Zhang, Engineering Properties of Rocks , Elsevier Science; 1st Edition, 2005.[7] M.N. Reddy and R. Pavanaguru, The geological setting of galaxy granite, unpublished paper.[8]PratapChandraSethy ,and Ashutosh Naik, Petrology, Geochemistry and Status of the Tikilipada Granite Gneiss, Sambalpur District, Odisha ,International Journal Of Earth Sciences & engineering, vol.07.no 02,pp.400-407,April 2014.

[9] Renjith S. Anand, and D. V. Reddy,A Geological and Geotechnical Investigation of some rocks in Trivandrum area, Kerala , un published paper.[10]Santosh.G.Hiremath , Geological and Geo -technical investigations of Ilkal Granites, Un Published M.Tech thesis, 2010.[11] SaffetYagiz, "P-wave velocity test for assessment of geotechnical properties of some rock materials", Bulletin of Materials Science, Vol. 34, No. 4, pp. 947953 July 2011.[12] Shah S. J., Soumya V. K., Rajeswari T. R., Compressive and Brazilian tests on rock samples from Malabar and Analysis of a Tunnel through Kuthiran, Proceedings of the Indian Geotechnical Conference, December 22-24, 2013, Roorkee, 2013.[13] Sivantha Reddy. G, Hanumathu R.C and Sreenivasulu. P, Dimensional Stone Granites of Chittoor district, Andhra Pradesh, India: An over view International Journal Of Earth Sciences & engineering, vol.06.no 03,pp.461-467,june 2013.[14] SomnathDasgupta, JurgenEhl, Michael M. Raith PulakSengupta PraneshSengupta Mid-crustal contact metamorphism around the Chimakurthy mafic-ultramafic complex, Eastern Ghats Belt, India, Contrib Mineral Petrol (1997) 129: 182-197[15] Venkat Reddy .D , B.R. Manjunatha, K.N. KrishnaKumar, K. Balakrishna, and G.P. Gurumurth Selection Criteria for Decorative Dimension Stones ,International Journal Of Earth Sciences & engineering, vol.07.no 02, pp.408-414, April 2014.[16] Venkat Reddy.D , Engineering Geology, Vikas Publishing House (P) Ltd., 2010.[17] A.S.T.M Designation: C1528 13,Standard Guide for Selection of Dimension Stone.[18] Relevant I.S.R.M standards[19] Relevant I.S codes.