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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 ...
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
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]
Sanguite; General; Category: Halides: Formula (repeating unit) KCuCl₃: IMA symbol: Sgu: Crystal system: monoclinic: Crystal class: 2/m: Space group: 2/ m - prismatic
Twinning is the intergrowth of two or more crystals of a single mineral species. 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.
As a rule, belomorite forms solid granular and crystalline masses or massive crystalline aggregates; crystals of tabular and tabular-prismatic types are much less common. Complex polysynthetic twinning is very often observed.