Bertossaite
Current inventory: 0 gems
 

  
Bertossaite was named to honor Antonio Bertossa, Director of the Geological Survey of Rwanda, the country in which it was first found.

Discovered in 1965; IMA status: Valid (IMA Approved 1965)

Chemistry

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

Classification

Mineral Classification:

Phosphates

Strunz 8th Ed. ID:

8/B.28-10

Nickel-Strunz 10th Ed. ID:

8.BH.25

8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H₂O
H : With medium-sized and large cations, (OH,etc.):RO₄ = 1:1

Related to:

Bertossaite-Palermoite Series. The calcium analogue of Palermoite.

Varieties:

None

Synonyms:

IMA1965-038

Crystal Data

Crystallography:

Orthorhombic

Crystal Habit:

Massive 

Twinning:

None

Physical Properties

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

Optical Properties

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

Occurances

Geological Setting:

Thought to be formed during a late calcium-rich phase of mineralization in a lithium-bearing granite pegmatite.

Common Associations:

Amblygonite, Lazulite-Scorzalite, Augelite, Brazilianite, Apatite, Crandallite, Trolleite, Samuelsonite, Quartz

Common Impurities:

Fe, Mn

Type Locality:

Buranga pegmatite, Gatumba District, Western Province, Rwanda

Year Discovered:

1965

View mineral photos:

Bertossaite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Bertossaite is a rare phosphate mineral from 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 determined by von Knorring and Mary E. Mrose in 1966. Bertossaite was named to honor Antonio Bertossa, Director of the Geological Survey of Rwanda.

For more than 35 years after its discovery Bertossaite was thought to be a one locatlity mineral until in 2003 Pierre Lefèvre investigated new samples of phosphates from the Rubindi-Kabilizi pegmatite, Rwanda, and discovered a new occurrence of Bertossaite 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 often found associated with Apatite, Brazilianite, Burangaite, Quartz, Scorzalite and Trolleite.

The picture above shows a gem with faintly-pink to white Bertossaite with blue Burangaite. Bertossaite is typically semi-transparent with vitreous luster and moderately strong dispersion and a Moh's hardness of 6. The combination of faintly pink to white Bertossaite and royal blue Burangaite makes for very attractive specimens and gems.

Bertossaite distribution: at the type locality in the Buranga pegmatite, near Gatumba, Rwanda. Also at the Rubindi-Kabilizi pegmatite, located 3 km WNW of Muhororo village, south of the Rubindi river, 50 km west of Kigali, Rwanda.
 

  
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