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-38545.jpg
Bertrandite from the Golconda pegmatite, Minas Gerais, Brazil
General
CategorySorosilicate
Formula
(repeating unit)
Be4Si2O7(OH)2
Strunz classification9.BD.05
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
H-M symbol: (mm2)
Space groupCcm21
Unit cella = 8.7135(4) Å,
b = 15.268(1) Å,
c = 4.5683(3) Å; Z = 4
Identification
ColorColorless to pale yellow
Crystal habitThin tabular, prismatic to needle-like crystals commonly in radial clusters
TwinningCommon on {011} or {021} forming heart or V shaped twins
CleavagePerfect on {001}; distinct on {100}, {010} and {110}
Mohs scale hardness6 - 7
LusterVitreous, pearly on cleavage surfaces
DiaphaneityTransparent
Specific gravity2.59 - 2.60
Optical propertiesBiaxial (-)
Refractive indexnα = 1.591 nβ = 1.605 nγ = 1.614
Birefringenceδ = 0.023
2V angleMeasured: 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]

See alsoEdit

ReferencesEdit

  1. ^ a b c Handbook of Mineralogy
  2. ^ a b Bertrandite on Mindat.org
  3. ^ a b 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.