Potassic-fluoro-hastingsite
Potassic-fluoro-hastingsite is a rare member of the Calcium Amphibole Subgroup of minerals that also includes Actinolite, Pargasite, Sadanagaite, Tremolite, and Tschermakite. The chemical formula of Potassic-fluoro-hastingsite is KCa2(Fe42+Fe3+)(Al2Si6O22)(F, OH)2 (Potassium Calcium Iron Aluminum Silicate Floride Hydroxide) and its molecular weight is 947.86 gm. Potassic-fluoro-hastingsite is very rare and obscure mineral and only found in one place in the world – the Greenwood Mine in the Town of Tuxedo, Orange County, New York, USA. It is rarely found in mineral collections and even rarer as a faceted gem! It is black with vitreous luster and is barely radioactive due to its potassium content.
Potassic-fluoro-hastingsite was discovered in 2005 in the tailings dump of the Greenwood (Patterson) iron mine. Potassic-fluoro-hastingsite has a specific gravity 3.289 (g/cm3) and the refractive index of 1.668 – 1.698 Biaxial ( – ). The mine, located in Hudson Highlands, in Harriman State Park, Town of Tuxedo, Orange County, New York, USA, was first opened in 1838, and was a source of iron during the Civil War. It was last worked in 1880.
This mineral was originally named Fluoro-potassic-hastingsite in 2009 by Marian V. Lupulescu, John Rakovan, M. Darby Dyer, George W. Robinson, and John M. Hughes for its chemical relationship to Hastingsite. But it was redefined and renamed in 2012 by the Amphibole Subcomittee of the Commission on New Minerals, Nomenclature and Classification (CNMNC). The new IMA approved name is Potassic-fluoro-hastingsite following the principle that the various prefixes to the root name are listed in the order they occur in the formula.
| Chemical Formula: | KCa2(Fe42+Fe3+)(Al2Si6O22)(F,OH)2 |
| Potassium Calcium Iron Aluminum Silicate Floride Hydroxide | |
| Molecular Weight: | 947.86 gm |
| Composition: | Potassium | 4.12 % | K | 4.97 % | K2O |
| Calcium | 8.46 % | Ca | 11.83 % | CaO | |
| Magnesium | 5.13 % | Mg | 8.50 % | MgO | |
| Aluminum | 5.69 % | Al | 10.76 % | Al2O3 | |
| Iron | 17.68 % | Fe | 15.16 % | FeO / 8.42 % Fe2O3 | |
| Silicon | 17.78 % | Si | 38.03 % | SiO2 | |
| Oxygen | 37.13 % | O | |||
| Fluorine | 4.01 % | F | 4.01 % | ||
| – % | F | -1.69 % | -O=F2 | ||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals prismatic; in compact aggregates to 1 cm |
| Twinning: | None |
| Cleavage: | Perfect on {110}, intersecting at 56° |
| Fracture: | Concoidal, sub-concoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.0 |
| Density: | 3.289 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Barely Detectable; GRapi = 58.40 (Gamma Ray American Petroleum Institute Units) |
| Color: | Black, dark greenish black on thin edges |
| Transparency: | Transparent to translucent |
| Luster: | Vitreous, sub-vitreous |
| Refractive Index: | 1.668 – 1.698 Biaxial ( – ) |
| Birefringence: | 0.030 |
| Dispersion: | Moderate to strong; r |
| Pleochroism: | Strong; X = bluish green; Y = greenish to brownish green; Z = blue to light blue |
