Azurite
De Dictionnaire geolien
Sommaire
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)