Mcallisterite

Formula:  Mg₂B₁₂O₁₄(OH)₁₂ ^. 9H₂O

Origin of name:  For J. McAllister, American geologist

Crystal system:  Hexagonal

Crystal class:  -3 2/m

Twinning: 

Unit cell: a = 11.543, c = 35.556

Colour:  Colourless, light amber

Diaphaneity:  Transparent

Luster: Vitreous

Habit:  Crystals rhombohedral, minute; as aggregates and nodular masses

Hardness:  2.5

Specific gravity:  1.867

Cleavage:  2; {0001} and {01-12} good

Tenacity: Brittle fracture

Streak: White

Synonyms/varieties:

Comments:  Dimorphous with admontite