Anorthite
Ca(Al2Si2O8)IMA symbol: Angrandfathered
Anorthite is a silicate mineral with the formula Ca(Al2Si2O8), crystallizing in the triclinic system. It has a Mohs hardness of 6-6.5, typically white, gray or red in color, a specific gravity of 17. Its streak is red; cleavage is perfect.
Photos
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Crystallography
| Crystal system | triclinic crystal systemWikidata (CC0) |
|---|---|
| Space group | C -1 |
| Cell (Å, °) | a = 8.131, b = 12.847, c = 7.069; α = 94.03, β = 115.9, γ = 90.72 |
| Cell volume | 661.839 ų, Z = 4 |
| Axial ratios | 0.6329:1:0.5502calculated from COD 9005309 |
| Source structure | COD 9005309 (European Journal of Mineralogy, 1997) — 1 of 17 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 3.182 | 3.168 | 3.241 | 4.018 | 3.2 | 3.109 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 86.4 | 58.9 | 54 | 53.6 | 43.1 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9005309; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 2.797 g/cm³calculated from COD 9005309 |
|---|---|
| Hardness (Mohs) | 6-6.5single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 17 g/cm3single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Color | gray, red, whitesingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | redsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Cleavage | perfectDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 278.21 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Ca 14.41%, Al 19.4%, Si 20.19%, O 46.01% |
Classification
| Nickel-Strunz (10th) | 9.FA.35Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 9.FA.35Wikidata (CC0) |
| Dana (8th) | 76.1.3.6Wikidata (CC0) |