Formula: Na3Ca(Si3Al3)O12S
Tectosilicate (framework silicate), sodalite group. Complete solid solution with nosean may exist, but is very limited with sodalite (Dana).
Crystal System: Isometric
Specific gravity: 2.38 to 2.45 measured, 2.4 calculated
Hardness: 8 to 8½
Streak: Bright blue
Colour: Ultramarine, midnight blue, bluish green, green
Common impurities: Fe,Mg,K,H2O

Igneous environments
Metamorphic environments

Most lazurites analysed to date represent only sulphide-rich varieties of haüyne and not a separate species (Mindat), so the information presented below may be more applicable to haüyne than to lazurite.

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).

At the Italian Mountain, Taylor Park, Dorchester Mining District, Gunnison county, Colorado, USA, lazurite formed early, apparently in equilibrium with diopside, forsterite and perhaps barium-bearing phlogopite, whereas grossular formed later. Thomsonite represents a late-stage hydrothermal alteration of lazurite. Thomsonite, chlorite and hisingerite, just beyond the lapis-lazuli zones, are also late minerals.
The deposits resulted from contact metamorphism of subgreywacke and sS dolostone by quartz monzonite and quartz diorite of the Tertiary (66.0 to 2.6 million years ago) Italian Mountain stocks. Sodium, sulphur, barium, strontium, chlorine and fluorine were introduced in aqueous magmatic fluids. Early baryte may have localised later barium-bearing phlogopite and lazurite. Late introduction of iron produced the iron-rich silicates, unusual in lapis-lazuli. Peak metamorphic conditions were pressure ~250 bars and temperature ~600oC (CM 18.59-70).

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