Ettringite
Ca6Al2(SO4)3(OH)12·26H2OIMA symbol: Ettapproved
Ettringite is a sulfate mineral with the formula Ca6Al2(SO4)3(OH)12·26H2O, crystallizing in the trigonal system. It has a Mohs hardness of 2-2.5, typically colorless in color, a specific gravity of 1.75. Its streak is white; cleavage is perfect.
Photos
Crystallography
| Crystal system | trigonal crystal systemWikidata (CC0) |
|---|---|
| Space group | P 3 1 c |
| Cell (Å, °) | a = 11.171, b = 11.171, c = 21.364; α = 90, β = 90, γ = 120 |
| Cell volume | 2308.86 ų, Z = 2 |
| Axial ratios | 1.0000:1:1.9125calculated from COD 9017146 |
| Source structure | COD 9017146 (American Mineralogist, 2019) — 1 of 5 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 9.674 | 5.585 | 3.86 | 2.551 | 2.197 | 4.676 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 59.2 | 51.6 | 46.5 | 42.4 | 37.7 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9017146; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 1.831 g/cm³calculated from COD 9017146 |
|---|---|
| Hardness (Mohs) | 2-2.5single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 1.75 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | colorlesssingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | whitesingle sourceWikidata (CC0) |
| Cleavage | perfectDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 1255.1 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Ca 19.16%, Al 4.3%, S 7.66%, O 63.74%, H 5.14% |
Classification
| Nickel-Strunz (10th) | 7.DG.15Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 7.DG.15Wikidata (CC0) |
| Dana (8th) | 31.10.2.1Wikidata (CC0) |