Bertrandite

Bertrandite is a beryllium sorosilicate hydroxide mineral with composition: Be₄Si₂O₇(OH)₂. Bertrandite is a colorless to pale yellow orthorhombic mineral with a hardness of 6-7.

Bertrandite
Bertrandite from the Golconda pegmatite, Minas Gerais, Brazil
General
Category	Sorosilicate
Formula (repeating unit)	Be4Si2O7(OH)2
Strunz classification	9.BD.05
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) H-M symbol: (mm2)
Space group	Ccm21
Unit cell	a = 8.7135(4) Å, b = 15.268(1) Å, c = 4.5683(3) Å; Z = 4
Identification
Color	Colorless to pale yellow
Crystal habit	Thin tabular, prismatic to needle-like crystals commonly in radial clusters
Twinning	Common on {011} or {021} forming heart or V shaped twins
Cleavage	Perfect on {001}; distinct on {100}, {010} and {110}
Mohs scale hardness	6 - 7
Luster	Vitreous, pearly on cleavage surfaces
Diaphaneity	Transparent
Specific gravity	2.59 - 2.60
Optical properties	Biaxial (-)
Refractive index	nα = 1.591 nβ = 1.605 nγ = 1.614
Birefringence	δ = 0.023
2V angle	Measured: 73° to 81°
References	[1][2][3]

It is commonly found in beryllium rich pegmatites and is in part an alteration of beryl. Bertrandite often occurs as a pseudomorphic replacement of beryl. Associated minerals include beryl, phenakite, herderite, tourmaline, muscovite, fluorite and quartz.[1]

It, with beryl, are ores of beryllium.

It was discovered near Nantes, France in 1883 and named after French mineralogist, Emile Bertrand (1844–1909).[1][2][3]

One of the world's largest deposits of bertrandite is Spor Mountain, Thomas Range, Utah which is currently the source of most of the world's beryllium production.[4][5]

See also

• List of minerals
• List of minerals named after people

References

1. Handbook of Mineralogy
2. Bertrandite on Mindat.org
3. Bertrandite on Webmineral
4. Fact Sheet 2016–3081 (October 2016). "Beryllium—A Critical Mineral Commodity—Resources, Production, and Supply Chain" (Article). usgs.gov/. pubs.usgs.gov: USGS. p. 4. Retrieved 16 May 2017.
5. Shawe, Daniel (1968). Ridge, John (ed.). Geology of the Spor mountain Beryllium District, Utah, in Ore deposits of the United States, 1933-1967. New York: The American Institute of Mining, Metallurgical, and Petroleum engineers, Inc. pp. 1148–1161.