Musgravite (Magnesiotaaffeite-6N’3S)
Current inventory:  0 gems
 

  
Musgravite is named for the Musgrave Ranges, South Australia, where it was first recognized.

Discovered in 1967;   IMA status:  Valid (IMA approved 2002)

Chemistry

Chemical Formula:

(Mg,Fe²⁺,Zn)₂Al₆BeO₁₂

Magnesium Iron Zinc Aluminum Beryllium Oxide

Molecular Weight:

426.60 gm

Composition:

Magnesium

9.69 %

Mg

16.06 %

MgO

Beryllium

1.90 %

Be

5.28 %

BeO

Aluminum

37.95 %

Al

71.70 %

Al₂O₃

Zinc

1.53 %

Zn

1.91 %

ZnO

Iron

3.93 %

Fe

5.05 %

FeO

Oxygen

45.00 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/B.07-30

Nickel-Strunz 10th Ed. ID:

4.FC.25

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
F : Hydroxides (without V or U)
C : Hydroxides with OH, without H₂O; corner-sharing octahedra

Related to:

Taaffeite Group. Chrysoberyl - Swedenburgite Series. 9R, 18R polytypoids.

Members of Group:

Taaffeite Group: Ferrotaaffeite-6N'3S (Pehrmanite), Magnesiotaaffeite-2N’2S (Taaffeite), Magnesiotaaffeite-6N’3S (Musgravite)

Varieties:

None

Synonyms:

Magnesiotaaffeite-6N3S, Musgravite

Crystal Data

Crystallography:

Trigonal - Hexagonal Scalenohedral

Crystal Habit:

Crystals platy on {0001}, to 0.5 mm; massive.

Twinning:

None

Physical Properties

Cleavage:

Perfect on {0001} (or a Parting); less Perfect on {1011}

Fracture:

Platy

Tenacity:

Brittle

Moh's Hardness:

8.0 - 8.5

Density:

3.68 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Light Olive Green, dark Greenish Blue, light to dark Violet; nearly Colorless in thin section

Transparency:

Transparent to Translucent

Luster:

Vitreous

Refractive Index:

1.719 - 1.739  Uniaxial ( - )

Birefringence:

0.0070

Dispersion:

n/a

Pleochroism:

None

Occurances

Geological Setting:

In a nodule, perhaps formerly a corundum crystal, in high-grade metapyroxenite, associated with metaperidotites and granulites (Musgrave Ranges, Australia); in pegmatite cutting granulite (Enderby Land, Antarctica).

Common Associations:

Phlogopite, Sapphirine, Spinel (Musgrave Ranges, Australia); Biotite, Garnet, Quartz, Sapphirine, Sillimanite, Surinamite (Enderby Land, Antarctica).

Common Impurities:

None

Type Locality:

Ernabella Mission, Musgrave Ranges, South Australia, Australia

Year Discovered:

1967, (IMA approved 2002)

View mineral photos:

Musgravite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Musgravite is one of the rarest of all gem species. Tested and certified faceted Musgravites are exceptionally rare. Musgravite is closely related to Taaffeite and the separation between the two is based on magnesium content. It is very difficult to distinguish Musgravite from Taaffeite. Their physical and optical properties are almost identical and the only sure way of determining one from the other is by Raman Spectroscopy. Musgravite and Taaffeite are two of the hardest of the extremely rare gem species with a hardness of 8.0 - 8.5 on the Moh's scale.

Musgravite was recently renamed by the IMA (International Mineralogical Association) and is now officially known as Magnesiotaaffeite-6N’3S. Musgravite was originally named after the Musgrave Ranges of Southern Australia where it was first discovered but has been renamed Magnesiotaaffeite-6N’3S by the IMA for its association with Taaffeite and its magnesium content. Musgravite was renamed as a method of clarifying the complexity of the compositions of Taaffeite Group minerals including Musgravite, Perhmanite and Taaffeite and the influences of the minerals Spinel and Nolanite on them.

So, according to the new nomenclature accepted by the IMA, Musgravite has become Magnesiotaaffeite-6N’3S, as it is composed of six modified Nolanite modules (6N) and three Spinel modules (3S). Correspondingly, Taaffeite has become Magnesiotaaffeite-2N’2S and Perhmanite has become Ferrotaaffeite-6N’3S. Taaffeite is now an IMA approved name for the group of minerals containing Musgravite (Magnesiotaaffeite-6N’3S), Perhmanite (Ferrotaaffeite-6N’3S) and Taaffeite (Magnesiotaaffeite-2N’2S). The names Musgravite and Taaffeite have been relegated to trade name status. However, I suspect that these names will continue to be used in the gem trade as the individual gem names.

Musgravite has been found at the Type Locality 16 km north-northeast of Ernabella Mission, Musgrave Ranges, South Australia; along Casey Bay, Enderby Land, Antarctica and at Dove Bugt, northeast Greenland. The only sources of facetable crystals are at Tunduru, Tanzania and a very limited find in 2009 at Mogok, Burma.
 

  
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