Tectosilicate (framework silicate), sodalite group. Complete solid solution with nosean may exist, but is very limited with sodalite (Dana).
Specific gravity: 2.38 to 2.45
Hardness: 8 to 8½
Streak: Bright blue
Colour: Ultramarine, midnight blue, bluish green, green
Lazurite occurs as a contact metamorphic mineral in
marble and skarn, and at
pegmatite-limestone contacts, Also in some
syenite and alkaline volcanics (Dana, HOM).
Associated minerals include calcite, pyrite, diopside, humite, forsterite, haüyne and muscovite (HOM, Mindat).
At the type locality, Ladjuar Medam, Sar-e Sang, Koksha Valley, Khash & Kuran Wa Munjan Districts, Badakhshan, Afghanistan, lazurite occurs in calcic skarn and marble (Mindat ). In the Koksha valley, lazurite pseudomorphs after muscovite have been found (KL p264).
Common impurities: Fe,Mg,K,H2O
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