Azurite

COLOR

Grey. Takes a good polish. Strong pleochroism.

REFLECTANCE

Quite low but relatively high compared to most gangue minerals: equal to malachite and siderite.

ANISOTROPISM

Strongly anisotropic. The anisotropism is partly masked by very beautiful, highly abundant blue internal reflections.

TEXTURE

Azurite occurs as less fibrous and thicker aggregates than malachite.

ASSOCIATED MINERALS

All the copper minerals; among primary sulfides, it is associated especially with enargite, famatinite and tetrahedrite-tennantite.

CRITERIA OF DETERMINATION

The grey color, strong pleochroism and anisotropism, and especially the abundant, deep blue internal reflections are highly characteristic, as is the association with primary copper minerals.

Source

ATLAS OF ORE MINERALS (P. Picot and Z. Johan)