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Albite, calcite, and pyrite often show polysynthetic twinning. 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.
Twinning: Common giving polysynthetic striae on {001} or {010} also contact, simple and multiple: Cleavage: ... Albite is a plagioclase feldspar mineral.
The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi 3 O 8 to CaAl 2 Si 2 O 8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or "record-groove" effect.
When viewed under a polarizing microscope, microcline exhibits a minute multiple twinning which forms a grating-like structure that is unmistakable. Feldspar (amazonite) Perthite is either microcline or orthoclase with thin lamellae of exsolved albite. Amazon stone, or amazonite, is a green variety of microcline.
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]
The name “belomorite” was given to this variety of albite by academician Alexander Fersman in 1925, based on the location of its discovery near the shore of the White Sea, and also by association — for the similarity of iridescence colors with the shades of sea water. The best varieties of belomorite are translucent or transparent, they ...
Anorthoclase is an intermediate member of the high albite – sanidine alkali feldspar solid solution series. Intermediate members of this series, high albite, anorthoclase and high sodium sanidine are stable at temperatures of 600 °C (1,100 °F) and above.
Ulexite displays polysynthetic twinning parallel to the elongation, along {010} and {100} (Murdoch, 1940). [11] In thin sections cut parallel to the fibers, ulexite grains display both length-fast and length-slow orientations in equal quantities because the intermediate axis (y) of the indicatrix is roughly parallel to the elongation of the ...