Tetradymite
Bi2Te2SIMA symbol: Ttdgrandfathered
Tetradymite is a sulfide or sulfosalt mineral with the formula Bi2Te2S, crystallizing in the trigonal system. It has a Mohs hardness of 1.5-2, typically gray in color, with a metallic luster, a specific gravity of 7.2-7.6. Cleavage is perfect.
Photos
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Crystallography
| Crystal system | trigonal crystal systemWikidata (CC0) |
|---|---|
| Space group | R -3 m :R |
| Cell (Å, °) | a = 10.31, b = 10.31, c = 10.31; α = 24.17, β = 24.17, γ = 24.17 |
| Cell volume | 161.469 ų, Z = 1 |
| Axial ratios | 1.0000:1:1.0000calculated from COD 9012420 |
| Source structure | COD 9012420 (Naturwissenschaften, 1939) — 1 of 6 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 3.173 | 2.159 | 2.34 | 1.785 | 3.71 | 1.375 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 37.8 | 32.9 | 19.3 | 16.9 | 16.5 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9012420; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 7.253 g/cm³calculated from COD 9012420 |
|---|---|
| Hardness (Mohs) | 1.5-2single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 7.2-7.6 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | graysingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | metallicsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Cleavage | perfectDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 705.23 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Bi 59.27%, Te 36.19%, S 4.55% |
Classification
| Nickel-Strunz (10th) | 2.DC.05Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 2.DC.05cWikidata (CC0) |