Aenigmatite

Formula:  Na₂Fe₅TiSi₆O₂₀

Origin of name:  from Greek for riddle, apparently an allusion to its (formerly) uncertain chemical composition

Crystal system:  Triclinic

Crystal class:  -1

Twinning:

Unit cell: a = 10.406 Å, b = 10.813 Å, c = 8.926 Å, a = 104°56', b = 96°52', g = 125°19'

Colour:  Black

Diaphaneity: Translucent to opaque

Luster:  Vitreous to greasy

Habit:  Crystals long prismatic; twining common; lamellar

Hardness:  5.5

Specific gravity:  3.74 to 3.85

Cleavage:  2; {010} and {100} good

Tenacity:

Streak:  Reddish brown

Synonyms/varieties:

Comments: Forms a series with wilkinsonite. A primary constituent in sodium-rich alkalic volcanics, pegmatites and other silica-poor igneous rocks