Helvite

Formula:  Mn₄Be₃(SiO₄)₃S

Origin of name:   From Greek for sun

Crystal system:  Cubic

Crystal class:  -43m

Twinning: 

Unit cell: a = 8.294 Ǻ

Colour:  Brown, reddish, gray, yellowish gray, yellow, yellowish green

Diaphaneity: 

Luster:  Vitreous to resinous

Habit:  Crystals tetrahedral, or octahedral in aspect; rounded aggregates

Hardness:  6

Specific gravity:  3.17 to 3.37

Cleavage:  1; {111} distinct

Tenacity:  Conchoidal to uneven; brittle

Streak:  White

Synonyms/varieties:

Comments:  Series with danalite and with genthelvite