Sillimanite
Al2SiO5IMA symbol: Silgrandfathered
Sillimanite is a silicate mineral with the formula Al2SiO5, crystallizing in the orthorhombic system. It has a Mohs hardness of 6-7, typically white, brown, gray or green in color, with an adamantine or vitreous luster, a specific gravity of 3.23-3.24. Its streak is red.
Photos
Crystallography
| Crystal system | orthorhombic crystal systemWikidata (CC0) |
|---|---|
| Space group | P b n m |
| Cell (Å, °) | a = 7.4857, b = 7.675, c = 5.7751; α = 90, β = 90, γ = 90 |
| Cell volume | 331.795 ų, Z = 4 |
| Axial ratios | 0.9753:1:0.7525calculated from COD 9006525 |
| Source structure | COD 9006525 (Physics and Chemistry of Minerals, 1997) — 1 of 18 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 3.364 | 3.415 | 2.205 | 2.542 | 1.519 | 2.679 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 80.3 | 69.5 | 50.9 | 45.5 | 27.7 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9006525; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 3.244 g/cm³calculated from COD 9006525 |
|---|---|
| Hardness (Mohs) | 7single sourceWikidata (CC0) 6-7single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 3.23-3.24 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | brown, gray, green, whitesingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | whitesingle sourceWikidata (CC0) redsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | adamantine, vitreoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 162.05 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Al 33.3%, Si 17.33%, O 49.37% |
Classification
| Nickel-Strunz (10th) | 9.AF.05Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 9.AF.05Wikidata (CC0) |