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| Bertrandite
is named in honor of French mineralogist Emile Bertrand
(1844 - 1909).
| Discovered
in 1883;
IMA
status: Valid (pre-IMA; Grandfathered) |
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Chemistry
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Chemical
Formula: |
Be4(Si2O7)(OH)2
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Beryllium
Silicate Hydroxide |
Molecular
Weight: |
238.23 gm
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Composition: |
Beryllium |
15.13 % |
Be |
42.00 % |
BeO |
|
Silicon |
23.58 % |
Si |
50.44 % |
SiO2 |
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Hydrogen |
0.85 % |
H |
7.56 % |
H2O |
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Oxygen |
60.44 % |
O |
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|
|
100.00 % |
|
100.00 % |
= TOTAL OXIDE |
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Classification
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Mineral
Classification: |
Silicates
(Germanates) |
Strunz 8th
Ed. ID:
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8/C.07-10
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Nickel-Strunz 10th
Ed. ID:
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9.BD.05
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9 : SILICATES (Germanates)
B : Sorosilicates D :
Si2O7 groups, with additional anions; cations in
tetrahedral [4] and greater coordination
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Related
to: |
Bertrandite-Strontiochevkinite Series.
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Varieties: |
Gel-Bertrandite
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Synonyms: |
Hessenbergite
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Crystal
Data
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Crystallography:
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Orthorhombic
- Pyramidal
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Crystal
Habit:
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Crystals
thin tabular, commonly prismatic to needlelike, to 5
cm; in radial aggregates.
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Twinning:
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Common
on [011] or [021]; twins heart-shaped or V-shaped with
axes crossing at angles of about 60° and 120°.
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Physical
Properties
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Cleavage: |
Perfect
on {001}; Distinct on {100}, {010}, and {110}
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Fracture: |
n/a
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Tenacity:
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Brittle
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Moh's
Hardness: |
6.0
- 7.0
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Density:
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2.59
- 2.60 (g/cm3)
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Luminescence:
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None
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Radioactivity:
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Not
Radioactive
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Other: |
Pyroelectric
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Optical
Properties
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Color: |
Colorless,
pale Yellow
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Transparency: |
Translucent
to Transparent |
Luster: |
Vitreous,
Pearly on cleavage {001} |
Refractive
Index: |
1.583
- 1.614
Biaxial ( - )
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Birefringence: |
0.0230
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Dispersion: |
Weak;
r < v |
Pleochroism: |
None
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Occurances
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Geological
Setting: |
In
fissures in granites and associated pegmatites and in
miarolitic cavities in greisens; commonly an alteration
product of beryl, more rarely as a primary mineral.
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Common
Associations: |
Beryl,
Fluorite, Herderite, Muscovite, Phenakite, Quartz, Tourmaline.
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Common
Impurities: |
Al,
Fe, Ca |
Co-Type
Localities: |
Barbin Quarry, Nantes, Loire-Atlantique, Pays de Loire,
France; Petit-Port, Nantes, Loire-Atlantique, Pays
de Loire, France |
Year
Discovered: |
1883
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View
mineral photos: |
Bertrandite
Mineral Photos and Locations |
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More
Information
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|
Mindat.org
Webmineral.com
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Bertrandite
is a fairly common mineral but rarely faceted since
crystals are rarely large enough or clean enough for
faceting. It is an important ore of beryllium second
only to Beryl. Bertrandite and Beryl are often found
associated together. Bertrandite is an alteration product
of Beryl and it is not unusual to find occurances of
Bertrandite completely replacing Beryl crystals forming
a psuedomorph. A psuedomorph is when one mineral replaces
another on an atom by atom basis, replacing the chemistry
and structure with the new mineral but preserving the
external shape of the original crystal. Bertrandite
gems are usually very small, colorless and included.
Bertrandite
is found in small amounts at numerous localities but
gem quality crystals are rare. A few locations include
Golconda mine, near Governador Valadares, Minas Gerais,
Brazil; Barbin quarries at Petit-Port, Loire-Atlantique,
France; Akchatau, Kara-Oba, and Kounrad, Kazakhstan;
and in the USA on Mt. Antero, Chaffee County, Colorado;
at the Strickland quarry, Portland, Middlesex County,
Connecticut.
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Bertrandite
gems for sale:
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have not photographed our Bertrandite gems
yet. Please
check back soon.
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