Albite Greenshist

The word schist is derived from the Greek word schízein meaning "to split", which is a reference to the ease with which schists can be split along the plane in which the platy minerals lie. A schist is a medium to coarse-grained, foliated, metamorphic rock typically containing muscovite, biotite, chlorite, and quartz. Feldspar, usually albite or oligoclase, also commonly occurs. A wide range of minerals are important as accessories and are characteristic either of the protolith composition or metamorphic grade. These minerals include graphite, garnet, staurolite, andalusite, kyanite, sillimanite, amphiboles, and epidote.

Schists form by regional metamorphism of a wide range of protoliths including argillaceous and arenaceous sediments, mixed siliciclastic and carbonate sediments and igneous rocks. Mica schists are derived mainly from argillaceous protoliths, whilst quartz and feldspar-rich schists have protoliths with a more significant arenaceous component. Graphite schists typically form from carbon-rich argillaceous sediments Calc-silicate schists, containing abundant carbonate minerals, and often including minerals such as tremolite, diopside and scapolite, can be derived from either mixed siliciclastic and carbonate sediments or altered igneous rocks. Schist is distinguished from high-grade gneiss by the lack of significant segregation into compositional bands, and usually has a smaller grain-size.

Bibliography

• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori.
• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc
• Anthony R. Phillpotts & Jay J. Ague: Principles of igneous and metamorphic petrology. Cambridge editore.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005)

Photo
Greenschist with Albite Porphyroblast. Sardinia (Italy). PPL image, 2x (Field of view = 7mm)	Greenschist with Albite Porphyroblast. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Greenschist with Albite Porphyroblast. Sardinia (Italy). PPL image, 2x (Field of view = 7mm)
Greenschist with Albite Porphyroblast. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Albite Porphyroblast in a Greenschist. Sardinia (Italy). XPL image, 10x (Field of view = 2mm)	Greenschist with Albite Porphyroblast. Sardinia (Italy). PPL image, 2x (Field of view = 7mm)
Greenschist with Albite Porphyroblast. Sardinia (Italy). PPL image, 2x (Field of view = 7mm)	Greenschist with Albite Porphyroblast. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Greenschist with Albite Porphyroblast. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)
Albite Porphyroblast in a Greenschist. Sardinia (Italy). PPL image, 10x (Field of view = 2mm)	Albite Porphyroblast in a Greenschist. Sardinia (Italy). XPL image, 10x (Field of view = 2mm)	Albite Porphyroblast in a Greenschist. Sardinia (Italy). PPL image, 10x (Field of view = 2mm)
Albite Porphyroblast in a Greenschist. Sardinia (Italy). XPL image, 10x (Field of view = 2mm)	Albite Porphyroblast in a Greenschist. Sardinia (Italy). XPL image, 10x (Field of view = 2mm)	Albite Porphyroblast in a Greenschist. Sardinia (Italy). XPL image, 10x (Field of view = 2mm)
Albite Porphyroblast in a Greenschist. Sardinia (Italy). XPL image, 10x (Field of view = 2mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 10x (Field of view = 2mm)
Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)
Albite Porphyroblasts in a Greenschist. Sardinia (Italy). PPL image, 2x (Field of view = 7mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). PPL image, 2x (Field of view = 7mm)
Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)	Albite Porphyroblasts in a Greenschist. Sardinia (Italy). XPL image, 2x (Field of view = 7mm)