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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 ...
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.
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 ...
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
Spurrite is a white, yellow or light blue mineral with monoclinic crystals. Its chemical formula is Ca 5 (Si O 4) 2 CO 3. [5]Spurrite is generally formed in contact metamorphism zones as mafic magmas are intruded into carbonate rocks. [6]
Microcline (cross-hatched twinning) included in magnetite (black, opaque) in plagioclase (polysynthetic twinning). Therefore, the sequence of formation is: microcline → magnetite → plagioclase. Peak porphyroblasts: A garnet-mica schist with porphyroblastic garnet (black) in fine-grained mica matrix: Retrograde (Post-peak) reaction rims
Simmonsite contains no observable euhedral crystals but it does have complex polysynthetic twinning. Its color is pale buff to cream in the hadn specimens accompanied by a white streak and has a greasy appearance. It exhibits a hardness of 2.5-3 on the Mohs hardness scale. There is no apparent cleavage, a subconchoidal fracture, no parting, and ...
Twinning is usual, and can occur as polysynthetic, which is when multiple twins align in a parallel. [4] It has a barely detectable 1.12% potassium radioactivity based on the GRapi unit (Gamma Ray American Petroleum Institute Units). [5]