plagioclase
Sign in to savethumb|Plagioclase displaying cleavage (crystal)|cleavage (unknown scale) thumb|In volcanic rocks, [[fine-grained plagioclase can display a "microlitic" texture of many small crystals.]]
Key facts
- Mineral.name
- Plagioclase
- Mineral.category
- Tectosilicate minerals
- Mineral.group
- Feldspar group
- Mineral.image
- Plagioklas1.jpg
- Mineral.caption
- A photomicrograph of a plagioclase crystal (gray) under cross polarized light. The plagioclase crystal shows a distinct banding effect called polysynthetic twinning.
- Mineral.formula
- NaAlSi3O8 – CaAl2Si2O8
- Mineral.IMAsymbol
- Pl
- Mineral.IMAstatus
- Mineral series
- Mineral.system
- Triclinic
- Mineral.class
- Pinacoidal ()
- Mineral.symmetry
- P (no. 2)
- Mineral.color
- White, gray, or bluish white
- Mineral.mohs
- 6–6.5
- Mineral.luster
- Vitreous
- Mineral.refractive
- Albite: nα 1.527, nβ 1.532 nγ 1.538Anorthite: nα 1.577 nβ 1.585 nγ 1.590
- Mineral.opticalprop
- Biaxial (+) albite, biaxial (-) anorthite
- Mineral.streak
- White
- Mineral.gravity
- 2.62 (albite) to 2.76 (anorthite)
via Wikipedia infobox
Article
14 sectionsContents
- Properties
- Plagioclase series members
- Endmembers
- Intermediate members
- Petrogenesis
- Classification of igneous rocks
- In metamorphic rocks
- In sedimentary rocks
- At the Mohorovičić discontinuity
- Exsolution
- Uses
- See also
- References
- External links
thumb|Plagioclase displaying cleavage (crystal)|cleavage (unknown scale) thumb|In volcanic rocks, [[fine-grained plagioclase can display a "microlitic" texture of many small crystals.]]
Plagioclase ( ) is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or "record-groove" effect.