General Information:
Chemical Formula:
Ca2Al2Si3O10(OH)2
Composition:
(Molecular Weight = 395.38 gm)
Calcium 20.27 % Ca
Aluminum 13.65 % Al
Silicon 21.31 % Si
Hydrogen 0.25 % H
Oxygen 44.51 % O
Empirical Formula:
Ca2Al2Si3O10(OH)
Environment:
Hydrothermally altered rocks.
Locality:
Haslach, Harzburg and Oberstein, Germany.
Name Origin:
Named after the Dutch Colonel, H. Von Prehn (1733-1785).
Physical Properties:
Cleavage:
[001] Distinct
Color:
colorless, gray, yellow, yellow green, or white.
Density:
2.8 - 2.95, Average = 2.87
Diaphaniety:
Subtransparent to translucent
Habits:
Reniform - "Kidney like" in shape (e.g.. hematite)., Globular - Spherical, or nearly so, rounded forms (e.g. wavellite)., Stalactitic - Shaped like pendant columns as stalactites or s talagmites (e.g. calcite).
Hardness:
6-6.5 - Orthoclase-Pyrite
Luminescence:
Non-fluorescent.
Luster:
Vitreous - Pearly
Streak:
colorless
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