Polyhalite
K2Ca2Mg(SO4)4·2H2OIMA symbol: Plhlgrandfathered
Polyhalite is a sulfate mineral with the formula K2Ca2Mg(SO4)4·2H2O, crystallizing in the triclinic system. It has a Mohs hardness of 2.5-3, typically red or yellow in color, with a pearly or resinous luster, a specific gravity of 2.769. Its streak is red.
Photos
.jpg){kind=link}
_10.jpg){kind=link}
.jpg){kind=link}
.jpg){kind=link}
Crystallography
| Crystal system | triclinic crystal systemWikidata (CC0) |
|---|---|
| Space group | P -1 |
| Cell (Å, °) | a = 6.975, b = 6.984, c = 8.899; α = 104.01, β = 101.19, γ = 114.1 |
| Cell volume | 362.337 ų, Z = 1 |
| Axial ratios | 0.9987:1:1.2742calculated from COD 9007992 |
| Source structure | COD 9007992 (Acta Crystallographica, Section E, 2005) — 1 of 2 structures |
Physical properties
| Density (calculated) | 2.745 g/cm³calculated from COD 9007992 |
|---|---|
| Hardness (Mohs) | 2.5-3single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 2.769 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | red, yellowsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | whitesingle sourceWikidata (CC0) redsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | pearly, resinoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 602.94 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | K 12.97%, Ca 13.29%, Mg 4.03%, S 21.27%, O 47.76%, H 0.67% |
Classification
| Nickel-Strunz (10th) | 7.CC.65Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 7.CC.65Wikidata (CC0) |