Magnesio-riebeckite
Current inventory:  0 gems
 

  
Magnesio-riebeckite was named in 1957 by Akiho Miashiro for its composition containing magnesium and its relationship to Riebeckite. Riebeckite is named for famous eighteenth century German explorer and minerologist, Emil Riebeck (1853 - 1885).

Discovered in 1949;  IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Na₂[(Mg,Fe²⁺)₃Fe³⁺₂]Si₈O₂₂(OH)₂

Sodium Magnesium Iron Silicate Hydroxide

Molecular Weight:

876.08 gm

Composition:

Potassium

0.13 %

K

0.16 %

K₂O

Sodium

4.09 %

Na

5.52 %

Na₂O

Calcium

1.97 %

Ca

2.75 %

CaO

Magnesium

5.35 %

Mg

8.88 %

MgO

Titanium

0.16 %

Ti

0.27 %

TiO₂

Manganese

0.31 %

Mn

0.45 %

Mn₂O₃

Aluminum

0.80 %

Al

1.51 %

Al₂O₃

Iron

17.47 %

Fe

12.06 %

FeO / 11.57 % Fe₂O₃

Silicon

25.65 %

Si

54.87 %

SiO₂

Hydrogen

0.23 %

H

2.06 %

H₂O

Oxygen

43.83 %

O

100.00 %

100.10 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

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:

Riebeckite Group, Sodium Amphibole Subgroup, w(OH, F, Cl)-dominant Amphibole Group, Amphibole Supergroup. Magnesioriebeckite - Ribeckite Series. Glaucophane - Riebeckite - Kozulite Series. Magnesio-riebeckite is defined as a member of the Riebeckite Group with Mg>Fe2+ in the C2+ position and (OH) in the W position.

Members of Group:

Riebeckite Group: Fluoro-riebeckite, Magnesio-fluoro-riebeckite, Riebeckite

Varieties:

None

Synonyms:

Babadudenite, Ferri-glaucophane, Magnesian-riebeckite, Rhodusite, Svidneite, Ternovskite, Torendikite, Torendrickite, Torendrikite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

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

Twinning:

Simple or multiple twinning || {100}.

Physical Properties

Cleavage:

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

Fracture:

Conchoidal to Uneven

Tenacity:

Brittle

Moh's Hardness:

5.0 - 6.0

Density:

3.12 - 3.29 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Health Warning:

The asbestiform variety of Magnesio-riebeckite can cause lung disease when inhaled, as in other species of asbestos minerals.

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. Veins in slightly metamorphosed sandstone and carbonates associated with evaporites.

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:

Magnesio-riebeckite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Magnesio-riebeckite is a rare gem that is not well known in the gem market. It is also known by the synonym Rhodusite which is named for the Greek island of Rhodes (Rhodus in historic times) where it was found by Bukowski in 1889. Magnesio-riebeckite is usually found as fibrous "asbestiform" masses but a very few sources produce solid, opaque, massive material of light to dark blue that can be used to create attractive cabochons.

Magnesio-riebeckite may have originally been discovered by C. Palache in 1928 at the mines at Franklin, New Jersey, USA, but the specimen was incorrectly identified as Crocidolite. The year of discovery is noted as 1949 from the type locality of Alto Chapare District, Chapare Province, Bolivia. Magnesio-riebeckite and Riebeckite are closely related to the mineral Glaucophane. Glaucophane is named for its typical blue color. The name Glaucophane is from the Greek glaukos for "sky-blue" and phainestrai for "to appear", in allusion to its typical color. The blue color is very diagnostic for the two species and both are the only common amphibole minerals that are typically blue.

There are many localities for finding the fibrous "asbestiform" material but only one source for the attractive solid, deep blue massive material: Krivoy Rog Basin, Dnipropetrovs'k Oblast' (Dnepropetrovsk Oblast'), Ukraine.
 

  
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