Wulfenite (Molybdate) 

Hardness: 3.0
Specific Gravity: 6.7 - 7.0

Characteristics: Usually orange red; vitreous, resinous, or adamantine luster; white streak; very dense; transparent to translucent; tabular tetragonal crystals; dissolves slowly in strong acids.

Found in oxidized lead deposits.

Wulfenite is a minor source of molybdenum; collected as mineral specimens.

(Primary text: Perkins, D. 2002. Mineralogy. Prentice Hall.)