Alum-(K)
Alum-(K) (also known as Potassium Alum) is a sulphate mineral that is very rarely available as a gem that is faceted. It is definitely a mineral that is unusual it is both barely radioactive and water soluble. It had been originally named Potassium Alum but was renamed to Alum-(K) by Mineralogical Record, v39 (2008), p131 to indicate that it’s the user that is k-dominant of Alum Group. Alum-(K) is often found in water purification, leather tanning, and fireproofing textiles. It also has aesthetic uses being an ingredient in deodorant and as an aftershave treatment due to its qualities that are astringent.
You will find very localities which can be few find gem quality crystals of Alum-(K). Many of these are the El Desierto mine, San Pablo de Napa, Daniel Campos Province, Potosí Department, Bolivia; Alaunhöhle, near Dresden, Saxony, Germany; Alum mine, Alum District, Esmeralda County, Nevada, USA; Alum King Mine, Marysvale District (Marysvale Uranium area), Piute County, Utah, United States Of America.
| Category: | Sulfate mineral |
| Chemical Formula: | KAl(SO4)2·12(H2O) |
| Hydrated Potassium Aluminum Sulfate | |
| Molecular Weight: | 474.39 gm |
| Composition: | Potassium | 8.24 % | K | 9.93 % | K2O |
| Aluminum | 5.69 % | Al | 10.75 % | Al2O3 | |
| Hydrogen | 5.10 % | H | 45.57 % | H2O | |
| Sulfur | 13.52 % | S | 33.75 % | SO3 | |
| Oxygen | 67.45 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Isometric – Diploidal |
| Crystal Habit: | Rarely as tiny octahedral crystals, if precipitated from pure water solution; cubic from alkaline solutions. Commonly stalactitic, columnar, granular, or massive efflorescences. |
| Twinning: | Very rare; on {111} |
| Cleavage: | {111} Poor/Indistinct, Interrupted |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 2.0 – 2.5 |
| Density: | 1.757 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Barely Detectable; GRapi = 124.32 (Gamma Ray American Petroleum Institute Units) |
| Other: | Soluble in water, taste sweetish and astringent; deliquesces at 91º C |
| Colour: | Colorless, White; Colourless in transmitted light |
| Transparency: | Transparent to Translucent |
| Lustre: | Vitreous |
| Refractive Index: | 1.456 Isotropic |
| Birefringence: | None (Isotropic); may be weakly anomalously birefringent and sectored |
| Dispersion: | n/a |
| Pleochroism: | None |
