Ice

Formula:  H₂O

Origin of name:  From German Eis

Crystal system:  Hexagonal

Crystal class:  6/m 2/m 2/m

Twinning: 

Unit cell: 

Colour:  Colourless; pale blue to greenish blue in thick layers

Diaphaneity:  Transparent

Luster:  Vitreous

Habit:  Crystals thin, flattened, six-rayed, or skeletal hexagonal prisms; delicate branching forms; hailstones

Hardness:  1.5

Specific gravity:  0.92

Cleavage:  None

Tenacity: 

Streak:  Colourless

Synonyms/varieties:

Comments:  Ice comes in at least 9 crystal forms, but only one in found in nature