Astrophyllite

Formula:  (K, Na)₃(Fe, Mn)₇Ti₂SI₈O₂₄(O, OH)₇

Origin of name:  From Greek astron = brilliant ( star) and phyllon = leaf, for the stellate and foliated micaceous habit

Crystal system:  Triclinic

Crystal class:  -1

Twinning:

Unit cell: a = 5.36 Å, b = 11.76 Å, c = 21.08 Å, a = 85°8', b = 90°0', g = 103°13'

Colour:  Bronze-yellow to golden yellow

Diaphaneity: Opaque to translucent in thin laminae

Luster:  Submetallic, pearly, greasy

Habit:  Crystals bladed or acicular; often in stellate groups

Hardness:  3

Specific gravity:  3.2 to 3.4

Cleavage:  2; {001} perfect, {100} poor

Tenacity: Brittle

Streak:  Golden, yellowish brown

Synonyms/varieties:

Comments:  Series with kupletskite. Member of astrophyllite group. Found in nepheline syenites, alkali granites, and their pegmatites; less commonly in fenites and other metasomatised rocks; in nepheline syenite gneisses and paragneisses.