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Bertrandite

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Formula:
Be4(Si2O7)(OH)2
System:
Orthorhombic
Colour:
Colourless, pale yellow.
Lustre:
Vitreous
Hardness:
6 - 7
Name:
For Emile Bertrand (1844-1909), French mineralogist.

Classification of Bertrandite

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
9.BD.05

9 : SILICATES (Germanates)
B : Sorosilicates
D : Si2O7 groups, with additional anions; cations in tetrahedral [4] and greater coordination
56.1.1.1

56 : SOROSILICATES Si2O7 Groups, With Additional O, OH, F and H2O
1 : Si2O7 Groups and O, OH, F, and H2O with cations in [4] coordination
14.3.2

14 : Silicates not Containing Aluminum
3 : Silicates of Be
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First Recorded Occurrence of Bertrandite

Place of Conservation of First Recorded Material:
National School of Mines, Paris, France
Year of Discovery:
1883

Occurrences of Bertrandite

Geological Setting:
Granite fissures or miarolitic cavities, pegmatites, greissen. Alteration product of beryl, rarely primary mineral.

Physical Properties of Bertrandite

Vitreous
Diaphaneity (Transparency):
Transparent
Comment:
Pearly on cleavage {001}
Colour:
Colourless, pale yellow.
Hardness (Mohs):
6 - 7
Cleavage:
Perfect
Perfect on {001}
Distinct on {100}, {010} and {110}
Density:
2.59 - 2.6 g/cm3 (Measured)    2.61 g/cm3 (Calculated)

Crystallography of Bertrandite

Crystal System:
Orthorhombic
Class (H-M):
mm2 - Pyramidal
Space Group:
Cmc21
Cell Parameters:
a = 8.7135(4) Å, b = 15.268(1) Å, c = 4.5683(3) Å
Ratio:
a:b:c = 0.571 : 1 : 0.299
Unit Cell Volume:
V 607.76 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Thin tabular, prismatic to needle-like
Twinning:
Common on {011}, {021}; heart- or V-shaped twins.

Crystallographic forms of Bertrandite

Crystal Atlas:
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Bertrandite no.19 - Goldschmidt (1913-1926)
Bertrandite no.20 - Goldschmidt (1913-1926)
Bertrandite no.21 - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by www.smorf.nl.

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Optical Data of Bertrandite

Type:
Biaxial (-)
RI values:
nα = 1.591 nβ = 1.605 nγ = 1.614
2V:
Measured: 73° to 81°, Calculated: 76°
Max Birefringence:
δ = 0.023
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
Moderate
Dispersion:
r < v weak

Chemical Properties of Bertrandite

Formula:
Be4(Si2O7)(OH)2
Essential elements:
All elements listed in formula:
Common Impurities:
Al,Fe,Ca

Relationship of Bertrandite to other Species

9.BD.10HemimorphiteZn4Si2O7(OH)2 · H2O
9.BD.15JunitoiteCaZn2Si2O7 · H2O
9.BD.20Axinite-(Fe)Ca2Fe2+Al2BSi4O15OH
9.BD.20Axinite-(Mg)Ca2MgAl2BSi4O15OH
9.BD.20Axinite-(Mn)Ca2Mn2+Al2BSi4O15(OH)
9.BD.20Tinzenite(CaMn2+)2Mn2+Al2BSi4O15(OH)
9.BD.25VistepiteSnMn4B2Si4O16(OH)2
9.BD.30BoralsiliteAl16B6Si2O37
9.BD.35Werdingite(Mg,Fe)2Al14Si4B4O37
14.3.1PhenakiteBe2SiO4
14.3.3BerylliteBe3(SiO4)(OH)2 · H2O
14.3.4LiberiteLi2BeSiO4
14.3.5ChkaloviteNa2BeSi2O6
14.3.6EudidymiteNa2Be2Si6O15 · H2O
14.3.7EpididymiteNa2Be2Si6O15 · H2O
14.3.8GugiaiteCa2Be(Si2O7)
14.3.9Jeffreyite(Ca,Na)2(Be,Al)(Si2O7,HSi2O7)
14.3.10Semenovite-(Ce)Na8Ca2FeBe6Ce2Si14O40(OH)4F4
14.3.11BaryliteBe2Ba(Si2O7)
14.3.12Hingganite-(Ce)(Ce,REE)2(□,Fe2+)Be2[SiO4]2(OH)2
14.3.13Hingganite-(Yb)(Yb,Y,REE)2□Be2[SiO4]2(OH)2
14.3.14Hingganite-(Y)(Y,REE,Ca)2(□,Fe2+)Be2[SiO4]2(OH)2
14.3.15Minasgeraisite-(Y)CaBe2Y2Si2O10
14.3.16SørenseniteNa4SnBe2Si6O16(OH)4
14.3.17TrimeriteCaMn22+Be3(SiO4)3
14.3.18ChiavenniteCaMnBe2Si5O13(OH)2 · 2H2O
14.3.19Tvedalite(Ca,Mn)4Be3Si6O17(OH)4 · 3H2O
14.3.20HarstigiteCa6(Mn,Mg)Be4Si6(O,OH)24
14.3.21SverigeiteNaMnMgSnBe2(SiO4)3(OH)
14.3.22Joesmithite{Pb}{Ca2}{Mg3Fe23+}(Be2Si6O22)(OH)2
14.3.23Gadolinite-(Y)Y2Fe2+Be2Si2O10
14.3.24Gadolinite-(Ce)(Ce,La,Nd,Y)2Fe2+Be2Si2O10
14.3.25Calciogadolinite-(Y)(YCa)2Fe3+Be2[SiO4]2O2

Other Names for Bertrandite

Name in Other Languages:
Simplified Chinese:羟硅铍石
Spanish:Bertrandita
Traditional Chinese:羥矽鈹石

Other Information

Electrical:
Pyroelectric
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Bertrandite

Reference List:
Neues Jahrbuch für Mineralogie, Monatshefte (1992): 13-19.

Internet Links for Bertrandite

Specimens:
The following Bertrandite specimens are currently listed for sale on minfind.com.

Localities for Bertrandite

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
Mineral and/or Locality  
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