Bertrandite
Be4Si2O7(OH)2IMA symbol: Btdgrandfathered
Bertrandite is a silicate mineral with the formula Be4Si2O7(OH)2, crystallizing in the orthorhombic system. It has a Mohs hardness of 6-7, typically colorless or yellow in color, with a pearly or vitreous luster, a specific gravity of 2.59-2.6. Cleavage is perfect.
Photos
Crystallography
| Crystal system | orthorhombic crystal systemWikidata (CC0) |
|---|---|
| Space group | C c m 21 |
| Cell (Å, °) | a = 15.19, b = 8.67, c = 4.53; α = 90, β = 90, γ = 90 |
| Cell volume | 596.6 ų, Z = 4 |
| Axial ratios | 1.7520:1:0.5225calculated from COD 1011283 |
| Source structure | COD 1011283 (Zeitschrift fuer Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie (-144,1977), 1932) — 1 of 5 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 2.51 | 4.335 | 2.265 | 2.195 | 3.146 | 3.882 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 75.4 | 74.2 | 74.2 | 64.9 | 50.8 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 1011283; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 2.641 g/cm³calculated from COD 1011283 |
|---|---|
| Hardness (Mohs) | 6-7single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 2.59-2.6 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | colorless, yellowsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | pearly, vitreoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Cleavage | perfectsingle sourceFord, Dana's Textbook of Mineralogy, 3rd ed. (1922) |
Chemistry (calculated)
| Molecular weight | 238.23 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Be 15.13%, Si 23.58%, O 60.44%, H 0.85% |
Classification
| Nickel-Strunz (10th) | 9.BD.05Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 9.BD.05Wikidata (CC0) |
| Dana (8th) | 56.1.1.1Wikidata (CC0) |