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  2. Plagioclase - Wikipedia

    en.wikipedia.org/wiki/Plagioclase

    Plagioclase of any composition shares many basic physical characteristics, while other characteristics vary smoothly with composition. [9] The Mohs hardness of all plagioclase species is 6 to 6.5, [12] and cleavage is perfect on [001] and good on [010], with the cleavage planes meeting at an angle of 93 to 94 degrees. [13]

  3. Anorthite - Wikipedia

    en.wikipedia.org/wiki/Anorthite

    Anorthite is a rare compositional variety of plagioclase. It occurs in mafic igneous rock. It also occurs in metamorphic rocks of granulite facies, in metamorphosed carbonate rocks, and corundum deposits. [3] Its type localities are Monte Somma and Valle di Fassa, Italy. It was first described in 1823. [5]

  4. Mohs scale - Wikipedia

    en.wikipedia.org/wiki/Mohs_scale

    For example, some sources have assigned a Mohs hardness of 6 or 7 to granite but it is a rock made of several minerals, each with its own Mohs hardness (e.g. topaz-rich granite contains: topaz — Mohs 8, quartz — Mohs 7, orthoclase — Mohs 6, plagioclase — Mohs 6–6.5, mica — Mohs 2–4).

  5. Feldspar - Wikipedia

    en.wikipedia.org/wiki/Feldspar

    The ratio of alkali feldspar to plagioclase feldspar, together with the proportion of quartz, is the basis for the QAPF classification of igneous rock. [ 15 ] [ 16 ] [ 17 ] Calcium-rich plagioclase is the first feldspar to crystallize from cooling magma, then the plagioclase becomes increasingly sodium-rich as crystallization continues.

  6. Albite - Wikipedia

    en.wikipedia.org/wiki/Albite

    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]

  7. Anorthosite - Wikipedia

    en.wikipedia.org/wiki/Anorthosite

    Anorthosite (/ ə ˈ n ɔːr θ ə s aɪ t /) is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%).

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  9. Labradorite - Wikipedia

    en.wikipedia.org/wiki/Labradorite

    Labradorite is an intermediate to calcic member of the plagioclase series. It has an anorthite percentage (%An) of between 50 and 70. The specific gravity ranges from 2.68 to 2.72. The streak is white, like most silicates. The refractive index ranges from 1.559 to 1.573 and twinning is common.