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Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula Na Al Si 3 O 8. It is a tectosilicate. Its color is usually pure white, hence its name from Latin, albus. [5]
Closely spaced polysynthetic twinning is often observed as striations or fine parallel lines on the crystal face. Cyclic twins are caused by repeated twinning around a rotation axis. This type of twinning occurs around three, four, five, six, or eight-fold axes, the corresponding patterns are called threelings, fourlings, fivelings , sixlings ...
Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or "record-groove" effect. Plagioclase is a major constituent mineral in Earth's crust and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks .
The geometry of the twinning is controlled by the mineral's symmetry. As a result, there are several types of twins, including contact twins, reticulated twins, geniculated twins, penetration twins, cyclic twins, and polysynthetic twins. Contact, or simple twins, consist of two crystals joined at a plane; this type of twinning is common in spinel.
Pericline is a form of albite exhibiting elongate prismatic crystals. [1] Pericline twinning is a type of crystal twinning which show fine parallel twin laminae typically found in the alkali feldspars microcline. [2] The twinning results from a structural transformation between high temperature and low temperature forms. [3]
Petrogenetic grid for metapelites (click to zoom). [1] [2] Each line represents a metamorphic reaction.Metamorphic facies included are: BS = Blueschist facies, EC = Eclogite facies, PP = Prehnite-Pumpellyite facies, GS = Greenschist facies, EA = Epidote-Amphibolite facies, AM = Amphibolite facies, GRA = Granulite facies, UHT = Ultra-High Temperature facies, HAE = Hornfels-Albite-Epidote facies ...
Anorthite crystals (white) in lava from Miyake Island, Japan (size: 2.4 × 1.7 × 1.7 cm) Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite (NaAlSi 3 O 8).
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms.It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of cell biology, Glossary of genetics, Glossary of evolutionary biology, Glossary of ecology ...