Gaudefroyite
Current inventory:  0 gems
 

  
Gaudefroyite is named in honor of Abbé Christophe Gaudefroy (1888-1971), French mineralogist who worked in Morocco.

Discovered in 1964;   IMA status:  Valid (IMA approved 1964)

Chemistry

Chemical Formula:

Ca₄Mn³⁺_3-X(BO₃)₃(CO₃)(O,OH)₃

Calcium Manganese Borate Hydroxide

Molecular Weight:

582.85 gm

Composition:

Calcium

27.51 %

Ca

38.49 %

CaO

Manganese

23.56 %

Mn

33.86 %

Mn₂O₃

Boron

5.56 %

B

17.92 %

B₂O₃

Hydrogen

0.13 %

H

1.16 %

H₂O

Carbon

2.06 %

C

7.55 %

CO₂

Oxygen

41.18 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Borates

Strunz 8th Ed. ID:

5/G.05-100

Nickel-Strunz 10th Ed. ID:

6.AB.60

6 : BORATES
A : Monoborates
B : BO₃, with additional anions; 1(D) + OH, etc.

Related to:

None

Varieties:

None

Synonyms:

IMA1964-006

Crystal Data

Crystallography:

Hexagonal - Pyramidal

Crystal Habit:

Crystals are stubby dipyramidal {1120}, or prismatic {0110} with prominent pyramidal terminations, to 5 cm; typically as stepwise tapered crystals in divergent aggregates.

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.0;  VHN = 840

Density:

3.35 - 3.50 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Black; in reflected light, Gray with strong Yellow-Orange to Reddish internal reflections.

Transparency:

Opaque, Transparent in thin slivers

Luster:

Vitreous to Dull, Adamantine to Resinous

Refractive Index:

w = 1.805 - 1.810 e = 2.015 - 2.020;  Uniaxial  ( + )

Birefringence:

0.210

Dispersion:

n/a

Pleochroism:

Strong; O = pale yellowish brown; E = red-orange. w = 1.81(1) e = 2.02(1)

Anisotrophism:

Strong, in pale gray

Occurances

Geological Setting:

An uncommon hydrothermal mineral in manganese deposits.

Common Associations:

Marokite, Braunite, Hausmannite, Crednerite, Pyrolusite, Calcite, Quartz, Brucite (Tachgagalt, Morocco); Barite, Calcite, Hydrogrossular, Manganite, Bixbyite, Braunite, Hausmannite, Hematite (Kuruman district, South Africa)

Common Impurities:

None

Type Locality:

Tachgagalt Mine, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco

Year Discovered:

1964

View mineral photos:

Gaudefroyite Mineral Photos and Locations

More Information

Mindat.org 
Webmineral.com

Gaudefroyite is a relatively rare Borate mineral but extremely rare as a faceted gem. Crystals are usually very small and thin to about 10 mm long by 5 mm wide. It is also a rare gem because it is black and undistinguished and only available as a collector's odity. Another rare gem for collectors of Black Gems.

There are only two main localities known for deposits of Gaudefroyite; at Tachgagalt, 17 km south-southwest of Ouarzazate, Anti-Atlas Mountains, Morocco. At the Black Rock, Wessels and N’Chwaning mines, Kalahari manganese fields, near Kuruman, Cape Province, South Africa.
 

  
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