Tridymite
SiO2IMA symbol: Trdgrandfathered
Tridymite is an oxide or hydroxide mineral with the formula SiO2, crystallizing in the orthorhombic system. It has a Mohs hardness of 7, typically colorless or white in color, with a pearly or vitreous luster, a specific gravity of 2.28-2.33. Its streak is white.
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Crystallography
| Crystal system | orthorhombic crystal systemWikidata (CC0) |
|---|---|
| Space group | A 1 a 1 |
| Cell (Å, °) | a = 25.878, b = 5.001, c = 18.526; α = 90, β = 117.69, γ = 90 |
| Cell volume | 2122.98 ų, Z = 48 |
| Axial ratios | 5.1746:1:3.7045calculated from COD 9013491 |
| Source structure | COD 9013491 (Journal of Mineralogical and Petrological Sciences, 2005) — 1 of 15 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 4.326 | 4.101 | 4.313 | 3.826 | 3.828 | 2.501 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 82.7 | 57.3 | 27.1 | 26.6 | 22.3 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9013491; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 2.256 g/cm³calculated from COD 9013491 |
|---|---|
| Hardness (Mohs) | 7single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 2.28-2.33 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | colorless, whitesingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | whitesingle sourceWikidata (CC0) |
| Luster | pearly, vitreoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 60.08 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Si 46.74%, O 53.26% |
Classification
| Nickel-Strunz (10th) | 4.DA.10Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 4.DA.10Wikidata (CC0) |
| Dana (8th) | 75.1.2.1Wikidata (CC0) |