Pentagonite

Formula: Ca(VO)Si₄O₁₀.4H₂O

Origin of name: from Greek for five and angle

Crystal system: orthorhombic

Crystal class: mm2

Twinning: common on {110} fivelings

Unit cell: a = 10.30 Å, b = 14.00 Å, c = 8.89 Å

Colour: blue, greenish blue

Diaphaneity: transparent

Luster: vitreous

Habit: crystals prismatic, elongated along c-axis, minute as spherulitic rosettes to 5 mm

Hardness: 3 to 4

Specific gravity: 2.33

Cleavage: 1; {010} good

Tenacity: 

Streak: 

Synonyms/varieties:

Comments: dimorphous with cavansite