Benitoite
Bertossaite is just a rare mineral that is phosphate the Buranga lithium pegmatite in Rwanda. It was originally described by Oleg von Knorring in 1965 from samples found in the Buranga pegmatite, Gatumba District, Western Province, Rwanda. He investigated the chemical properties in 1965 but the physical properties of Bertossaite were later decided by von Knorring and Mary E. Morse in 1966. Bertossaite was named to honour Antonio Bertossa, Director of this Geological Survey of Rwanda.
For more than 35 years after its discovery, Bertossaite was considered one locality mineral until in 2003 Pierre Lefèvre investigated brand new samples of phosphates from the Rubindi-Kabilizi pegmatite, Rwanda, and discovered an event that is new of in veins cross-cutting Montebrasite, Scorzalite, and Brazilianite. This research was part of Lefèvre’s Master’s thesis at the University of Liège, Liège, Belgium. Bertossaite is usually found 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 normally 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 makes for very attractive specimens and gems.
Bertossaite distribution: during the type locality into the Buranga pegmatite, near Gatumba, Rwanda. Also at the Rubindi-Kabilizi pegmatite, found 3 WNW that is km of the village, south of the Rubindi river, 50 km west of Kigali, Rwanda.
| Category: | Cyclosilicate |
| Chemical Formula: | BaTiSi3O9 |
| Barium Titanium Silicate | |
| Molecular Weight: | 413.46 gm |
| Composition: | Barium | 33.21 % | Ba | 37.08 % | BaO |
| Titanium | 11.58 % | Ti | 19.32 % | TiO2 | |
| Silicon | 20.38 % | Si | 43.60 % | SiO2 | |
| Oxygen | 34.83 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Hexagonal – Ditrigonal Dipyramidal |
| Crystal Habit: | Flat pyramidal crystals, tabular, triangular or hexagonal in outline, to 6 cm. |
| Twinning: | By rotation about [0001] |
| Cleavage: | Poor on [1011] |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.0 – 6.5 |
| Density: | 3.64 – 3.68 (g/cm3) |
| Luminescence: | Fluorescent; blue under SW UV; intense blue Cathodoluminescence |
| Radioactivity: | Not Radioactive |
| Color: | Sapphire-blue, purplish-blue, white to colorless, pink; commonly bicolored. |
| Transparency: | Transparent to translucent |
| Luster: | Vitreous |
| Refractive Index: | 1.756 – 1.804 Uniaxial ( + ) |
| Birefringence: | 0.047 |
| Dispersion: | 0.046 (greater than diamond) |
| Pleochroism: | Visible; O = colorless; E = purple, indigo, greenish blue |
