Polylithionite
Polylithionite is named from the Greek word poly meaning many or much, in allusion to its composition with a high LITHIum content. The chemical formula of Polylithionite is KLi2AlSi4O10 (F, OH)2 (Potassium Lithium Aluminum Silicate Fluoride) and its molecular weight is 393.12 gm. Polylithionite is a member of the Mica Group of minerals that also includes Celadonite, Lepidolite, Muscovite, and Phlogopite. Polylithionite has a specific gravity of 2.58 – 2.82 (g/cm3) and the refractive index of 1.530 – 1.559 Biaxial ( – ). Polylithionite can often be found as attractive rosette crystal clusters resembling the petals of a flower and often associated with Sérandite. Polylithionite is rarely available as a gemstone but a recent find in Pakistan has produced gemmy Pollucite crystals containing tiny crystal inclusions of Polylithionite. Magnification must be used to observe these tiny Polylithionite crystals which have good crystal forms. Polylithionite may fluoresce lemon yellow to pale yellowish white under shortwave UV light.
Locations for Polylithionite: On the Kangerdluarssuk Plateau and elsewhere in the Ilímaussaq intrusion, southern Greenland. In Russia, found on Mts. Karnasurt and Lepke-Nelm, Lovozero massif, Kola Peninsula. In the Dara-i-Pioz massif, Alai Range, Tien Shan, Tajikistan. At Vøra, Sandefjord, Oslo region, Norway. From Mont Saint-Hilaire and near Saint-Amable, Quebec, Canada. In the USA, at Point of Rocks, Colfax County, New Mexico. On Mt. Malosa, Zomba district, Malawi.
| Chemical Formula: | KLi2AlSi4O10 (F,OH)2 |
| Potassium Lithium Aluminum Silicate Fluoride | |
| Molecular Weight: | 393.12 gm |
| Composition: | Potassium | 9.95 % | K | 11.98 % | K2O |
| Sodium | 1.75 % | Na | 2.36 % | Na2O | |
| Lithium | 3.00 % | Li | 6.46 % | Li2O | |
| Aluminum | 6.86 % | Al | 12.97 % | Al2O3 | |
| Silicon | 28.58 % | S | 61.14 % | SiO2 | |
| Hydrogen | 0.26 % | H | 2.29 % | H2O | |
| Oxygen | 44.77 % | O | |||
| Fluorine | 4.83 % | F | 4.83 % | F | |
| — | — % | F | -2.03 % | -O=F2 | |
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Pseudohexagonal crystals, tabular || f001g, to 10 cm. As irregularly shaped aggregates of fine scaly crystals. |
| Twinning: | None |
| Cleavage: | Perfect on {001} |
| Fracture: | Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 2.0 – 3.0 |
| Density: | 2.58 – 2.82 (g/cm3) |
| Luminescence: | May fluoresce lemon-yellow under SW UV |
| Radioactivity: | Barely Detectable; GRapi = 141.95 (Gamma Ray American Petroleum Institute Units) |
| Color: | Bright to pale pink, cream to white, colorless, pale brown to yellow-brown, bluish, greenish; in transmitted light, colorless |
| Transparency: | Transparent |
| Luster: | Pearly to waxy when fine-grained |
| Refractive Index: | 1.530 – 1.559 Biaxial ( – ) |
| Birefringence: | 0.025 – 0.029 |
| Dispersion: | Weak |
| Pleochroism: | n/a |
