Bertrandite
Current inventory:  0 gems
 

  
Bertrandite is named in honor of French mineralogist Emile Bertrand (1844 - 1909).

Discovered in 1883;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Be₄(Si₂O₇)(OH)₂

Beryllium Silicate Hydroxide

Molecular Weight:

238.23 gm

Composition:

Beryllium

15.13 %

Be

42.00 %

BeO

Silicon

23.58 %

Si

50.44 %

SiO₂

Hydrogen

0.85 %

H

7.56 %

H₂O

Oxygen

60.44 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/C.07-10

Nickel-Strunz 10th Ed. ID:

9.BD.05

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

Related to:

Bertrandite-Strontiochevkinite Series.

Varieties:

Gel-Bertrandite

Synonyms:

Hessenbergite

Crystal Data

Crystallography:

Orthorhombic - Pyramidal

Crystal Habit:

Crystals thin tabular, commonly prismatic to needlelike, to 5 cm; in radial aggregates.

Twinning:

Common on [011] or [021]; twins heart-shaped or V-shaped with axes crossing at angles of about 60° and 120°.

Physical Properties

Cleavage:

Perfect on {001}; Distinct on {100}, {010}, and {110}

Fracture:

n/a

Tenacity:

Brittle

Moh's Hardness:

6.0 - 7.0

Density:

2.59 - 2.60 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Pyroelectric

Optical Properties

Color:

Colorless, pale Yellow

Transparency:

Translucent to Transparent

Luster:

Vitreous, Pearly on cleavage {001}

Refractive Index:

1.583 - 1.614  Biaxial ( - )

Birefringence:

0.0230

Dispersion:

Weak; r < v

Pleochroism:

None

Occurances

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.

Common Associations:

Beryl, Fluorite, Herderite, Muscovite, Phenakite, Quartz, Tourmaline.

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

View mineral photos:

Bertrandite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

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.
 

  
Bertrandite gems for sale:

We have not photographed our Bertrandite gems yet. Please check back soon.