Hardness: 6.0 - 7.0
Specific Gravity: 3.4 - 3.5
Characteristics: Colors vary from black to yellowish green; vitreous to dull luster; often as coatings on other minerals; sometimes prismatic crystals; perfict cleavage in one direction; insoluble in most acids.
Found in hydrothermal veins in granitic plutons; amphibolites; basalts.
(Primary text: Perkins, D. 2002. Mineralogy. Prentice Hall.)