Ettringite

Formula:   Ca6 Al2(SO4)3(OH)12 . 26H2O

Origin of name:   Locality; Ettringen, Germany

 

Crystal system:   Hexagonal

Crystal class:   3m

Twinning:

Unit cell: 

 

Colour:  Colourless, milky white

Diaphaneity:  Transparent

Luster:   Vitreous

Habit:   Flattened hexagonal dipyramids; prismatic; fibrous

Hardness:   2 to 2.5

Specific gravity:   1.77

Cleavage:   1; {10-10} perfect

Tenacity: 

Streak: 

 

Synonyms/varieties:   Woodfordite (SiO2, CO2-rich var.)

 

Comments:

 

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