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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 ...
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]
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 .
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]
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).
Example on bottom where albite (Na Al Si 3 O 8) changes to anorthite (Ca Al 2 Si 2 O 8), Al 3+replaces Si 4+ and Ca 2+ for Na +. Coupled substitution is the geological process by which two elements simultaneous substitute into a crystal in order to maintain overall electrical neutrality and keep the charge constant. [1]
Anorthoclase and high albite exhibit triclinic symmetry, whereas sanidine and the low temperature orthoclase have monoclinic symmetry. [6] If the high temperature intermediate composition alkali feldspars are allowed to cool slowly, exsolution occurs and a perthite structure results.
Reaction centers are present in all green plants, algae, and many bacteria.A variety in light-harvesting complexes exist across the photosynthetic species. Green plants and algae have two different types of reaction centers that are part of larger supercomplexes known as P700 in Photosystem I and P680 in Photosystem II.