Orthoclase
K(AlSi3O8)IMA symbol: Orapproved
Orthoclase is a silicate mineral with the formula K(AlSi3O8), crystallizing in the monoclinic system. It has a Mohs hardness of 6-6.5, typically colorless, white, gray or green in color, with a vitreous luster, a specific gravity of 2.5-2.62. Its streak is red.
Photos
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Crystallography
| Crystal system | monoclinic crystal systemWikidata (CC0) |
|---|---|
| Space group | C 1 2/m 1 |
| Cell (Å, °) | a = 8.5739, b = 12.9874, c = 7.2018; α = 90, β = 116.042, γ = 90 |
| Cell volume | 720.521 ų, Z = 4 |
| Axial ratios | 0.6602:1:0.5545calculated from COD 9017214 |
| Source structure | COD 9017214 (European Journal of Mineralogy, 2013) — 1 of 25 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 3.313 | 3.235 | 3.774 | 4.224 | 2.992 | 3.288 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 79.4 | 75.6 | 61 | 59.5 | 57 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9017214; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 2.555 g/cm³calculated from COD 9017214 |
|---|---|
| Hardness (Mohs) | 6single sourceWikidata (CC0) 6-6.5single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 2.5-2.62 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | colorless, gray, green, red, white, yellowsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | whitesingle sourceWikidata (CC0) redsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | vitreoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 278.33 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | K 14.05%, Al 9.69%, Si 30.27%, O 45.99% |