anorthite
Sign in to saveAnorthite (2Si2O8. Anorthite is found in igneous rocks.
Key facts
- Mineral.name
- Anorthite
- Mineral.category
- Tectosilicate minerals
- Mineral.group
- Feldspar group
- Mineral.series
- Plagioclase feldspar series
- Mineral.image
- Anorthite-rare08-38b.jpg
- Mineral.caption
- Anorthite crystals in a basalt vug from Vesuvius (size:6.9 × 4.1 × 3.8 cm)
- Mineral.formula
- CaAl2Si2O8 or (Na:Ca = 0:100 to 10:90)
- Mineral.IMAsymbol
- An
- Mineral.IMAstatus
- Grandfathered (1823)
- Mineral.strunz
- 9.FA.35
- Mineral.system
- Triclinic
- Mineral.class
- Pinacoidal ()
- Mineral.symmetry
- P (no. 2)
- Mineral.unit cell
- a = 8.1768, b = 12.8768 c = 14.169 [Å]; α = 93.17° β = 115.85°, γ = 92.22°; Z = 8
- Mineral.color
- White, grayish, reddish
- Mineral.habit
- Anhedral to subhedral granular
- Mineral.twinning
- Common
- Mineral.cleavage
- Perfect [001] good [010] poor [110]
via Wikipedia infobox
Article
4 sectionsContents
- Mineralogy
- Occurrence
- See also
- References
Anorthite (2Si2O8. Anorthite is found in igneous rocks.
==Mineralogy == thumb|left|Anorthite crystals (white) in lava from Miyake Island, Japan (size: 2.4 × 1.7 × 1.7 cm) Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite (NaAlSi3O8). Pure anorthite, containing no sodium, is rare on Earth. Anorthite also refers, however, to plagioclase compositions with more than 90 molecular percent of the anorthite endmember (and up to 10 molecular percent of the albite endmember). The composition of plagioclases is often expressed as a molar percentage of An%, or (for a specific quantity) Ann, where n = Ca/(Ca + Na) × 100. This equation predominantly works in a terrestrial context; exotic locales and in particular Lunar rocks may need to account for other cations, such as Fe2+, to explain differences between optically and structurally derived An% data observed in Lunar anorthites.