Åkermanite

Formula: Ca₂MgSi₂O₇

Origin of name:  For Anders Åkerman (1837-1922), Swedish metallurgist

Crystal system:  Tetragonal

Crystal class:  -42m

Twinning: On {100} and {001}, cruciform

Unit cell: a = 7.829 Å, c = 5.005 Å

Colour:  Colourless, grayish, green, brown

Diaphaneity: Transparent to translucent

Luster:  Vitreous to resinous

Habit:  Crystals short prismatic to thin tabular; commonly massive granular

Hardness:  5 to 6

Specific gravity:  2.944

Cleavage: 2; {001} distinct, {110} indistinct

Tenacity: Brittle

Streak: White

Synonyms/varieties:

Comments: Member of the melilite group. Forms a series with gehlenite. Product of contact metamorphism of siliceous limestones and dolostones, and in rocks of sanidinite facies. Also formed from alkalic magma rich in calcium