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Sellaite
Current inventory:  1 gem
 

Chemistry:  MgF₂

Discovered in 1868;   IMA status: Valid (pre-IMA; Grandfathered).
Sellaite is named after the Italian mining engineer and minerologist Quintino Sella (1827-1884).

Classification

Mineral Classification:

Halides

Strunz 8th Ed. ID:

3/A.06-10

Nickel-Strunz 10th Ed. ID:

3.AB.15

3 : HALIDES
A : Simple halides, without H₂O
B : M:X = 1:2

Related to:

Sellaite Series

Crystal Data

Crystallography:

Tetragonal - Ditetragonal Dipyramidal

Crystal Habit:

Crystals are stout prismatic to acicular. Also fibrous aggregates.

Twinning:

On [011]

Physical Properties

Cleavage:

[100] Distinct, [110] Distinct

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.14 - 3.15 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Very slightly soluble in water.

Optical Properties

Color:

Colorless, White

Transparency:

Transparent

Luster:

Vitreous

Refractive Index:

1.378 - 1.390  Uniaxial ( + )

Birefringence:

0.0120

Dispersion:

0.014 (low)

Pleochroism:

None

Occurances

Geological Setting:

In bituminous dolomite-anhydrite rock in a glacial moraine.

Common Associations:

Anhydrite, Gypsum, Sulphur

Type Locality:

Gébroulaz glacier, Val Thorens, Savoie, Rhône-Alpes, France

Year Discovered:

1868

View mineral photos:

Sellaite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Sellaite is an exceedingly rare gem. Crystals from Brazil are the only current facetable material. Crystals are very small with very little transparent area for faceting. Sellaite is a Halide mineral along with Boleite, Fluorite and Villiaumite.

Sellaite is an interesting mineral in that it forms in a wide variety of geologic environments. It forms in a bituminous dolomite-anhydrite rock (Gebroulaz glacier, France); in evaporites (Bleicherode, Germany); in volcanic ejecta and fumarolic deposits (Vesuvius, Italy); in marble (Carrara, Italy); in a metamorphic magnesite deposit (Brumado mine, Brazil); and in an alkalic granite (Lake Gjerdingen, Norway).
 

  
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