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Properties. Plagioclase is the most common and abundant mineral group in the Earth's crust. Part of the feldspar family of minerals, it is abundant in igneous and metamorphic rock, and it is also common as a detrital mineral in sedimentary rock. [6] [7] It is not a single mineral, but is a solid solution of two end members, albite or sodium ...
- 6–6.5
- Pinacoidal (1), (same H-M symbol)
- Biaxial (+) albite, biaxial (-) anorthite
- Triclinic
Plagioclase is a solid solution series of albite and anorthite, with various names and compositions based on their relative abundance. It is the most abundant feldspar in igneous and metamorphic rocks, and some varieties are used as gems or building stones.
- Silicate
- White
- Vitreous. Pearly on some cleavage faces.
Plagioclase Feldspar properties. Typically white to gray, may also range from colorless, through shades of off-white, to yellowish, pink, reddish brown or nearly black. One perfect cleavage and one good cleavage that meet at nearly 90°. Increases from 2.6 to 2.8 depending on amount of calcium.
The plagioclase Mineral Series. The Plagioclase series is a group of related feldspar minerals that essentially have the same formula but vary in their percentage of sodium and calcium. Albite and Anorthite are the end members of the series, with the intermediary minerals Oligoclase, Andesine, Labradorite, and Bytownite.
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Plagioclase is a feldspar mineral series that forms a solid-solution series between albite and anorthite. It occurs in various rocks and has applications in glass, ceramics, and gemstones.
- The Editors of Encyclopaedia Britannica
Aug 11, 2018 · Basically, 50% rule says that Na dominant plagioclase is now albite and Ca dominant is anorthite. However, the old plagioclases names are still used in petrology for classification of rocks. The discarded plagioclase feldspars include oligoclase (10-30% of albite), andesine (30-50%), labradorite (50-70%) and bytownite (70-90%).
Plagioclase is a series of Na- and Ca-bearing aluminosilicates that occur in most igneous, metamorphic, and sedimentary rocks. Learn about its structure, chemistry, properties, twinning, alteration, and how to identify it in thin section and in hand specimen.
