Penkvilksite

Formula: Na₄Ti₂Si₈O₂₂.5H₂O

Origin of name: from Lapp penk = curly and vilkis = white

Crystal system: orthorhombic

Crystal class: 2/m 2/m 2/m

Twinning: 

Unit cell: 

Colour: colourless

Diaphaneity: transparent

Luster: vitreous, pearly or silky on fracture surface

Habit: anhedral crystals , up to 1 mm long

Hardness: 5

Specific gravity: 2.63

Cleavage: 1; perfect

Tenacity: 

Streak: white

Synonyms/varieties:

Comments: data are for penkvilksite-2O, there is also a -1M polytype