Bastnasite
Bastnäsite (also spelt Bastnaesite) is an extremely rare gem and one of the few rare earth element (REE) carbonate minerals. Bastnäsite may be weakly radioactive as defined in 49 CFR 173.403 (greater than 70 Bq/gramme) due to the presence of the rare earth element (REE) Cerium (64%). Bastnäsite and Monazite both contain Cerium (Ce) and are the two largest sources of Cerium. Gems are usually small and moderately included.
Bastnäsite is one of the unusual minerals that exhibit the piezoelectric effect. Piezoelectricity is the ability of some mineral crystals to generate a voltage in response to applied mechanical stress such as an external pressure. Piezoelectricity was discovered in 1880 by French physicists, brothers Jacques and Pierre Curie.
Bastnäsite distribution: Shinwaro, Kunar Province, Afghanistan; Mont Saint-Hilaire, Quebec, Canada; Andakatany, Ambatofangehana, Madagascar; Zegi Mountain, Fata, Pakistan; Karonge, Burundi; Wigu Hill, Tanzania; Nkombwa Hill, Zambia; and several locations in the USA including near Stove Mountain, in the St. Peters Dome area, and at Crystal Park, near Pikes Peak, El Paso County, Colorado.
| Category: | Carbonate mineral |
| Chemical Formula: | Ce(CO3)F |
| Cerium Carbonate Fluoride | |
| Molecular Weight: | 219.12 gm |
| Composition: | Cerium | 63.94 % | Ce | 74.90 % | Ce2O3 |
| Carbon | 5.48 % | C | 20.08 % | CO2 | |
| Oxygen | 21.90 % | O | |||
| Fluorine | 8.67 % | F | 8.67 % | F | |
| – | – % | F | -3.65 % | -O=F2 | |
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Hexagonal – Ditrigonal Dipyramidal |
| Crystal Habit: | Commonly in tabular to equant crystals, may be modified, horizontally striated, may be elongated, commonly in syntactic intergrowth with röntgenite-(Ce), synchysite-(Ce), Parisite-(Ce), or cordiality-(Ce), to 20 cm; granular, massive. |
| Twinning: | None |
| Cleavage: | Imperfect on {1011}, Indistinct on {0001} |
| Fracture: | Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 4.0 – 4.5 |
| Density: | 4.90 – 5.20 (g/cm3) |
| Luminescence: | Dark red Cathodoluminescence |
| Radioactivity: | Weak; GRapi = 60,386.61 (Gamma Ray American Petroleum Institute Units) |
| Other: | Strongly Piezoelectric. Soluble in strong, hot acids. May be found as pseudomorphs after Fluocerite or Tscheffkinite. |
| Colour: | Wax Yellow, Honey Yellow, Reddish Brown |
| Transparency: | Transparent to Translucent |
| Lustre: | Vitreous to Greasy, Pearly |
| Refractive Index: | 1.717 – 1.823 Uniaxial ( + ) |
| Birefringence: | 0.1010 |
| Dispersion: | 0.013 |
| Pleochroism: | Weak; faintly pleochroic when absorption E is greater than O. |
