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Magnesioriebeckite
Current inventory:  1 gem
 

Chemistry:  Na₂Mg₃Fe³⁺₂(Si₈O₂₂)(OH)₂

Discovered in 1949;   IMA status: Valid (pre-IMA; Grandfathered).
Magnesioriebeckite is named for its composition containing magnesium and its relatinship to Riebeckite. Riebeckite is named for famous eighteenth century German explorer and minerologist, Emil Riebeck (1853 - 1885).

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/F.08-40

Nickel-Strunz 10th Ed. ID:

9.DE.25

9 : SILICATES (Germanates)
D : Inosilicates
E : Inosilicates with 2-periodic double chains, Si₄O₁₁; Clinoamphiboles

Related to:

Amphibole Group. Sodic Clino - Amphibole Subgroup. Magnesioriebeckit - Ribeckite Series. Glaucophane - Riebeckite - Kozulite Series.

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Rarely as prismatic crystals. Also columnar, fibrous, or granular aggregates.

Twinning:

Simple or multiple twinning.

Physical Properties

Cleavage:

[110] Perfect; intersecting at ~58° and ~122°; partings on [010], [001].

Fracture:

Conchoidal to Uneven

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.12 - 3.29 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Light Blue, Dark Blue, Blackish Blue, Black

Transparency:

Translucent to Opaque

Luster:

Vitreous, Silky

Refractive Index:

1.668 - 1.680  Biaxial ( - ) or ( + )

Birefringence:

0.0120

Dispersion:

r > v or r < v

Pleochroism:

Strong; X = dark blue; Y = indigo; Z = yellow-green

Occurances

Geological Setting:

In granulites, ironstones, ferruginous metacherts, greenschist facies schists, and carbonatites.

Common Associations:

Epidote, Muscovite, Quartz, Stilpnomelane, Winchite

Common Impurities:

Ti, Al, Mn, Ca, K, H₂O

Type Locality:

Alto Chapare District, Chapare Province, Cochabamba Department, Bolivia

Year Discovered:

1949

View mineral photos:

Magnesioriebeckite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Magnesioriebeckite is a very rare gem that is not well know in the gem market. It is also known as Rhodusite (name origin unknown). Magnesioriebeckite is usually found as fibrous "asbestiform" masses but a few sources produce solid, opaque, prismatic crystals of light to dark blue that can be used to create attractive cabochons.

Magnesioriebeckite may have originally been discovered by C. Palache in 1928 at the mines at Franklin, New Jersey, USA, but was incorrectly identified as Crocidolite. The year of discovery is noted as 1949 from the type locality of Alto Chapare District, Chapare Province, Bolivia.

There are many localities for finding the fibrous "asbestiform" material but only one source for the attractive blue crystals: Kokchetav Massif, Kazakhstan.
 

  
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