• What if we had staurolite and andalusite together? What conditions would that indicate?

Epidote Group

• Sorosilicates (paired silicate tetrahedra)

• Include the mineral Epidote Ca2FeAl2Si3O12(OH), Zoisite (Ca2Al3Si3O12(OH) and clinozoisite (polymorph)

Garnets

Garnet (001) view blue = Si purple = A turquoise = BGarnet (001) view blue = Si purple = A turquoise = B

Garnet: AGarnet: A2+2+33 B B3+3+

22 [SiO [SiO44]]3 3

““Pyralspites”Pyralspites” - B = Al - B = AlPyPyrope: Mgrope: Mg33 Al Al22 [SiO [SiO44]]3 3

AlAlmandine: Femandine: Fe33 Al Al22 [SiO [SiO44]]33

SpSpessartine: Mnessartine: Mn33 Al Al22 [SiO [SiO44]]33

““Ugrandites”Ugrandites” - A = Ca - A = CaUUvarovite: Cavarovite: Ca33 Cr Cr22 [SiO [SiO44]]33

GrGrossularite: Caossularite: Ca33 Al Al22 [SiO [SiO44]]33

AndAndradite: Caradite: Ca33 Fe Fe22 [SiO [SiO44]]33

Occurrence:Occurrence:Mostly metamorphicMostly metamorphicSome high-Al igneousSome high-Al igneousAlso in some mantle peridotitesAlso in some mantle peridotites

Staurolite• Aluminosilicate - Fe2Al9Si4O22(OH)2

• Similar structure to kyanite with tetrahedrally coordinated Fe2+ easily replaced by Zn2+ and Mg2+

• Medium-grade metamorphic mineral, typically forms around 400-500 C– chloritoid + quartz = staurolite + garnet– chloritoid + chlorite + muscovite = staurolite + biotite +

quartz + water

• Degrades to almandine (garnet at higher T)– staurolite + muscovite + quartz = almandine +

aluminosilicate + biotite + water

Metamorphic chain silicates

• Actinolite and tremolite are chain silicates derived from dolomite and quartz and common in low-mid grade metamorphic rocks

• Riebeckite and Glaucophane are also chain silicates – higher grade minerals, often a blue color

• These minerals usually lower P, higher T conditions

Metamorphic Facies• Where do we find

these regimes of P-T ‘off’ of the typical continental isotherms??

• How is the environment that forms a blueschist facies rock different from one forming a hornfels?

• Table 25-1. The definitive mineral assemblages that characterize each facies (for mafic rocks).

Metamorphic Facies

• Miyashiro (1961) initially proposed five facies series, most of them named for a specific representative “type locality” The series were:

1. Contact Facies Series (very low-P)

2. Buchan or Abukuma Facies Series (low-P regional)

3. Barrovian Facies Series (medium-P regional)

4. Sanbagawa Facies Series (high-P, moderate-T)

5. Franciscan Facies Series (high-P, low T)

Facies Series

Fig. 25-3.Fig. 25-3. Temperature-Temperature-pressure diagram pressure diagram showing the three showing the three major types of major types of metamorphic metamorphic facies series facies series proposed by proposed by Miyashiro (1973, Miyashiro (1973, 1994). 1994). Winter Winter (2001) An (2001) An Introduction to Introduction to Igneous and Igneous and Metamorphic Metamorphic Petrology. Petrology. Prentice Hall.Prentice Hall.

Isograds

• Lines (on a map) or Surfaces (in the 3D world) marking the appearance or disappearance of the Index minerals in rocks of appropriate compositione.g. the ‘garnet-in isograd’; the ‘staurolite-out isograd’Complicated by the fact that most of these minerals are solid solutions

• Isograds for a single shale unit in southern Vermont

• Which side reflects a higher grade, or higher P/T environment?

Meteorite/ Comet Impacts

• P/T space??

Energy of an impact

• Kinetic energy – going from very fast to stopping is a BIG change in energy

• What happens to that energy??

• Impactite – any mineral formed as a result of this impact Shatter cone

Materials indicating Meteorite Impacts

• Tektites• Glass formed from impact

Diaplectic Glass

• Glass formed through fusion of different minerals – not melted, but fused…

What Happens to minerals that are there but not melted?

• Shock Quartz

• Lamellae retaining evidence of impact

Diamonds

• Very small diamonds can form from impacts and are found in meteorite impact craters around the world

Quartz Polymorphs• Coesite and Stishovite found associated with

impact craters