Adularia
Adularia is a variety of Orthoclase which will be is just a known member of the Potassium Feldspars of the Feldspar Group of minerals that includes Adularia, Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone, Oligoclase, Orthoclase, Sanidine and Sunstone. Adularia is generally found in “Alpine-type” formations but rarely as gem quality crystals. Although Adularia is many often known from Alpine (Alps) localities, there are several “Alpine-type” localities into the Himalayas of Pakistan that also create some specimens being great.
Most Adularia crystals are milky opaque and white to translucent. Seldom, Adularia gems are transparent as well as eye clean and may show a light color that is blue when rotated in the light. This sheen is the motivation for the expression “adularescence” which is named for the gem kind.
Adularia is normally discovered in areas of the Alps including several valleys of the Hohe Tauern Mountains, Salzburg, Austria; the Apuan Alps, Lucca Province, Tuscany, Italy; several valleys in the Alps of Switzerland. Adularia is also found in the Astore District, Northern Areas, Pakistan.
| Chemical Formula: | KAlSi3O8 |
| Potassium Aluminum Silicate | |
| Molecular Weight: | 278.33 gm |
| Composition: | Potassium | 14.05 % | K | 16.92 % | K2O |
| Aluminum | 9.69 % | Al | 18.32 % | Al2O3 | |
| Silicon | 30.27 % | Si | 64.76 % | SiO2 | |
| Oxygen | 45.99 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals commonly short prismatic along [100] or [001], tabular on [010], to 20 cm. Cleavable, granular, massive. |
| Twinning: | Common as simple, contact, or penetration twins according to the Carlsbad, Baveno, or Manebach laws. |
| Cleavage: | Perfect on {001} and {010}; partings on {100}, {110}, {110}, and {201} |
| Fracture: | Conchoidal to Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.0 – 6.5 |
| Density: | 2.55 – 2.63 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Barely Detectable; GRapi = 200.97 (Gamma Ray American Petroleum Institute Units) |
| Optical Properties | |
| Color: | Colorless, White, Gray, pale Yellow, Colorless in thin section; may exhibit opalescence or schiller iridescence. |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous, Pearly on cleavages |
| Refractive Index: | 1.518 – 1.525 Biaxial ( – ) |
| Birefringence: | 0.004 – 0.005 |
| Dispersion: | Distinct; r > v |
| Pleochroism: |
None |
