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  2. Cleavage (geology) - Wikipedia

    en.wikipedia.org/wiki/Cleavage_(geology)

    The cleavage domains are darker biotite grains, and the microlithons between consist of mostly muscovite and quartz. The grains in the microlithons are starting to align in a preferred orientation. A new foliation overprinted an old, showing the beginning signs of a crenulation cleavage.

  3. Cleavage (crystal) - Wikipedia

    en.wikipedia.org/wiki/Cleavage_(crystal)

    Cleavage forms parallel to crystallographic planes: [1] Basal, pinacoidal, or planar cleavage occurs when there is only one cleavage plane. Talc has basal cleavage. Mica (like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets. Prismatic cleavage occurs when there are two cleavage planes in a crystal ...

  4. Quartz - Wikipedia

    en.wikipedia.org/wiki/Quartz

    Quartz is, therefore, classified structurally as a framework silicate mineral and compositionally as an oxide mineral. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. [10] Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation ...

  5. Crystal twinning - Wikipedia

    en.wikipedia.org/wiki/Crystal_twinning

    Quartz – Japan twin Diagram of twinned crystals of albite.On the more perfect cleavage, which is parallel to the basal plane (P), is a system of fine striations, parallel to the second cleavage (M).

  6. Mineral - Wikipedia

    en.wikipedia.org/wiki/Mineral

    Cleavage is not a universal property among minerals; for example, quartz, consisting of extensively interconnected silica tetrahedra, does not have a crystallographic weakness which would allow it to cleave. In contrast, micas, which have perfect basal cleavage, consist of sheets of silica tetrahedra which are very weakly held together. [82] [83]

  7. Extinction (optical mineralogy) - Wikipedia

    en.wikipedia.org/wiki/Extinction_(optical...

    Undulose extinction in quartz. Extinction is a term used in optical mineralogy and petrology, which describes when cross-polarized light dims, as viewed through a thin section of a mineral in a petrographic microscope. Isotropic minerals, opaque (metallic) minerals, and amorphous materials (glass) do not allow light transmission under cross ...

  8. Thin section - Wikipedia

    en.wikipedia.org/wiki/Thin_section

    In thin section, quartz grain provenance in a sedimentary rock can be estimated. In crossed polarized light, the quartz grain can go extinct all at once, called monocrystalline quartz, or in waves, called polycrystalline quartz. The extinction in waves is called undulose extinction and indicates dislocation walls in mineral grains. Dislocation ...

  9. Chalcedony - Wikipedia

    en.wikipedia.org/wiki/Chalcedony

    Chalcedony (/ k æ l ˈ s ɛ d ə n i / kal-SED-ə-nee or / ˈ k æ l s ə ˌ d oʊ n i / KAL-sə-doh-nee) [2] is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. [3] These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic.