Sellaite

Formula: MgF2

Origin of name: for Q. Sella, Italian mining engineer

 

Crystal system: tetragonal

Crystal class: 4/m 2/m 2/m

Twinning: on {011}

Unit cell: a = 4.623 Å, c = 3.052 Å

 

Colour: colourless, white

Diaphaneity: transparent

Luster: vitreous

Habit: crystals stubby prismatic to acicular, fibrous aggregates

Hardness: 5

Specific gravity: 3.14 to 3.15

Cleavage: 2; {10} and {110} perfect

Tenacity: conchoidal, brittle

Streak: 

 

Synonyms/varieties:

 

Comments: structurally related to rutile

 

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