Hydroxyapophyllite

Formula:  KCa₄Si₈O₂₀(OH,F) ^. 8H₂O

Origin of name:  From hydroxyl and apophyllite

Crystal system:  Tetragonal

Crystal class:  4/m 2/m 2/m

Twinning: 

Unit cell: a = 8.978 Ǻ, c = 15.83 Ǻ

Colour:  Colourless to white, yellow and green tinges

Diaphaneity: 

Luster:  Vitreous to pearly

Habit:  Crystals equant or tabular

Hardness:  4.5 to 5

Specific gravity:  2.37

Cleavage:  1; {001} perfect

Tenacity: 

Streak:  White

Synonyms/varieties:

Comments:  Series with fluorapophyllite