Volborthite

Volborthite is a mineral containing copper and vanadium, formula Cu3V2O7(OH)2·2H2O. Found originally in 1838 in the Urals, it was named for Alexander von Volborth (1800-1876), a Russian paleontologist.
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(n.)
A mineral occurring in small six-sided tabular crystals of a green or yellow color. It is a hydrous vanadate of copper and lime.
  

General Information:
 Chemical Formula:
Cu++3V+++++2O7(OH)2·2(H2O)
 Composition:
(Molecular Weight = 474.56 gm)
Vanadium 21.47 % V 
Copper 40.17 % Cu
Hydrogen 1.27 % H 
Oxygen 37.09 % O 
 Empirical Formula:
Cu3V5+2O7(OH)2·2(H2O)
Physical Properties:
 Cleavage:
[???] Imperfect
 Color:
brownish yellow, greenish yellow, yellow, yellow green, or light brown.
 Density:
3.5
 Diaphaniety:
Translucent to Subtranslucent
 Habits:
Globular - Spherical, or nearly so, rounded forms (e.g. wavellite)., ,
 Hardness:
3 - Calcite
 Luminescence:
Non-fluorescent.
 Luster:
Vitreous - Pearly
 Streak:
light green
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