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