Bertossaite
Bertossaite is a rare mineral that is phosphate the Buranga lithium pegmatite in Rwanda. It was initially described by Oleg von Knorring in 1965 from examples discovered in the Buranga pegmatite, Gatumba District, Western Province, Rwanda. He investigated the chemical properties in 1965 but the real properties of Bertossaite were later on determined by von Knorring and Mary E. Morse in 1966. Bertossaite ended up being named to honour Antonio Bertossa, Director of the Geological Survey of Rwanda.
For over 35 years after its discovery Bertossaite was regarded as a single locality mineral until in 2003 Pierre Lefèvre investigated new samples of phosphates from the Rubindi-Kabilizi pegmatite, Rwanda, and discovered an occurrence that is brand new of in veins cross-cutting Montebrasite, Scorzalite, and Brazilianite. This investigation was part of Lefèvre’s Master’s thesis at the University of Liège, Liège, Belgium. Bertossaite is generally discovered associated with Apatite, Brazilianite, Burangaite, Quartz, Scorzalite and Trolleite.
The image above shows a gem with faintly-pink to Bertossaite that is white with Burangaite. Bertossaite is usually semi-transparent with vitreous lustre and dispersion that is moderately strong a Moh’s hardness of 6. The combination of faintly pink to Bertossaite that is white and blue Burangaite produces very attractive specimens and gems.
Bertossaite distribution: at the type locality in the Buranga pegmatite, near Gatumba, Rwanda. Also during the Rubindi-Kabilizi pegmatite, located 3 WNW that is km of the village, south regarding the Rubindi river, 50 km western of Kigali, Rwanda.
| Chemical Formula: | (Li,Na)2(Ca,Fe2+,Mn2+)Al4(PO4)4(OH,F)4 |
| Lithium Sodium Calcium Iron Manganese Aluminum Phosphate Hydroxide Fluoride | |
| Molecular Weight: | 609.80 gm |
| Composition: | Lithiium | 2.28 % | Li | 4.90 % | Li2O |
| Calcium | 6.57 % | Ca | 9.20 % | CaO | |
| Aluminum | 17.70 % | Al | 33.44 % | Al2O3 | |
| Phosphorus | 20.32 % | P | 46.55 % | P2O5 | |
| Hydrogen | 0.66 % | H | 5.91 % | H2O | |
| Oxygen | 52.47 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Orthorhombic |
| Crystal Habit: | Massive |
| Twinning: | None |
| Cleavage: | Good on {100} |
| Fracture: | Irregular/Uneven to sub-conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.0 |
| Density: | 3.10 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Pale pink; colorless in transmitted light |
| Transparency: | Semi-transparent |
| Luster: | Vitreous |
| Refractive Index: | 1.624 – 1.642 Biaxial ( – ) |
| Birefringence: | 0.018 |
| Dispersion: | Moderately strong, r < v |
| Pleochroism: | None |
