| Anorthite | |
|---|---|
 | |
| General | |
| Category | Feldspar |
| Formula (repeating unit) | CaAl2Si2O8 |
| IMA symbol | An[1] |
| Strunz classification | 9.FA.35 |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal (1) (same H-M symbol) |
| Space group | P1 |
| Unit cell | a = 8.1768, b = 12.8768 c = 14.169 [Å]; α = 93.17° β = 115.85°, γ = 92.22°; Z = 8 |
| Identification | |
| Formula mass | 278.203 g·mol−1 |
| Color | White, grayish, reddish |
| Crystal habit | Anhedral to subhedral granular |
| Twinning | Common |
| Cleavage | Perfect [001] good [010] poor [110] |
| Fracture | Uneven to conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.72–2.75 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.573–1.577 nβ = 1.580–1.585 nγ = 1.585–1.590 |
| Birefringence | δ = 0.012–0.013 |
| 2V angle | 78° to 83° |
| Melting point | 1553 °C[2] |
| References | [3][4][5] |
Anorthite (an = not, ortho = straight) is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is CaAl2Si2O8. Anorthite is found in mafic igneous rocks. Anorthite is rare on the Earth[6] but abundant on the Moon.[7]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ J.R. Goldsmith (1980): The melting and breakdown reactions of anorthite at high pressures and temperatures. Am. Mineralogist. 65, 272-284, http://www.minsocam.org/ammin/AM65/AM65_272.pdf
- ^ Handbook of Mineralogy
- ^ Mindat
- ^ Webmineral
- ^ Deer, W.A., Howie, R.A. and Zussman, J. (1966). An Introduction to the Rock Forming Minerals. London: Longman. p. 336. ISBN 0-582-44210-9.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ "Significant Lunar Minerals" (PDF). In Situ Resource Utilization (ISRU). NASA. Archived from the original (PDF) on 27 May 2010. Retrieved 23 August 2018.