May 7 2013
Bertrandite is a beryllium sorosilicate hydroxide that often occurs as a replacement of beryl. It was discovered near Nantes, France in 1883 and named after Emile Bertrand, a French mineralogist.
Properties of Bertrandite
The following are the key properties of Bertrandite:
- Cell Data
- Space Group: Cmc21
- a = 8.7135(4)
- b = 15.268(1)
- c = 4.5683(3)
- Z = 4
- Crystal Data
- Orthorhombic
- Point Group: mm2
- Crystals thin tabular, commonly prismatic to needlelike, to 5 cm
- Radial aggregates
- Twinning: Common on {011} or {021}
- Twins heart-shaped or V-shaped with axes crossing at angles of about 60° and 120°
- X-ray powder pattern: 4.38 (100), 3.19 (90), 2.54 (80), 2.28 (60), 2.22 (50), 3.94 (40), 1.305 (40)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| SiO2 |
49.26 |
50.44 |
| BeO |
42.0 |
42.00 |
| H2O |
6.90 |
7.56 |
| Fe2O3 |
1.40 |
- |
| Al2O3 |
trace |
- |
| Total |
99.56 |
100.00 |
- Optical Properties
- Optical Class: Biaxial (-)
- Orientation: X = a; Y = b
- Dispersion: r < v; weak
- α = 1.583-1.591
- β = 1.598-1.605
- γ = 1.608-1.614
- 2V(meas.) = ~75°
- Estimated Properties
| Electron density |
Bulk density (electron density)=2.57 g/cm3
note: Specific gravity of Bertrandite =2.60 g/cm3 |
| Photoelectric |
PEBertrandite = 1.07 barns/electron
U= PEBertrandite x ρElectron density= 2.75 barns/cm3 |
| Fermion index |
Fermion index = 0.16
Boson index = 0.84 |
| Radioactivity |
Bertrandite is not radioactive |
How to Identify Bertrandite
Bertrandite occurs in pale yellow or colorless forms. It has translucent to transparent appearance. It is a non-fluorescent mineral with a vitreous luster, a white streak and perfect cleavages. The fractures appear brittle as displayed by glasses and most of the non-metallic minerals. Its crystals are prismatic in shape. It has an average density of 2.59 g/cm3 and its relative hardness ranges from 6 to 7.
Global Distribution
Bertrandite is distributed in the following places:
- Near Nantes, in the Barbin quarries at Petit-Port, Loire-Atlantique, France
- At Val Vigezzo, Piedmont, Italy
- Pisek, Czech Republic
- Strickland
- Strickland quarry, Portland, Middlesex Co., Connecticut
- Amelia, Amelia Co., Virginia
- Mt. Antero, Chaffee Co., Colorado
- Spor Mountain, Juab Co., Utah
- San Diego Co., California
- Sierra de Aguachile, Acuna, Coahuila, Mexico
- Golconda mine, near Governador Valadares, Minas Gerais, Brazil
- Klein Spitzkopje, Namibia
- Tae Hwa mine, Chung Cheong Buk Do, South Korea
- Akchatau, Kara-Oba
- Kounrad, Kazakhstan.
Occurrence of Bertrandite and Useful Mineral Association
Bertrandite occurs in the fissures in granites, related pegmatites and also in miarolitic cavities in greisens. It is an alteration product of beryl, and very rarely as a primary mineral. It is closely associated with quartz, fluorite, muscovite, tourmaline, herderite, phenakite and beryl.
References