Lazurite

Mineral

Lazurite appears in shades from deep blue to greenish-blue, a color caused by S3− anions. It ranks 5.0 to 5.5 on the Mohs hardness scale, has a specific gravity of 2.4, and is translucent with a refractive index of 1.50. The mineral melts at 3.5 on Wolfgang Franz von Kobell’s fusibility scale and dissolves in hydrochloric acid. It often contains or is found alongside pyrite grains.

Formed through contact metamorphism of limestone, lazurite typically occurs with calcite, pyrite, diopside, humite, forsterite, hauyne, and muscovite. Other blue minerals like azurite and lazulite can be mistaken for lazurite but are identifiable under close inspection; lazurite was once considered a synonym for azurite. First described in 1890 from the Sar-e-Sang District in Afghanistan’s Koksha Valley, it has been mined in the Badakhshan lapis lazuli region for over 6,000 years and used as a pigment in painting and cloth dyeing since at least the 6th or 7th century.

Additional sources include Siberia’s Lake Baikal, Mount Vesuvius, Burma, Canada, and the United States. The name comes from the Persian word lajvard, meaning blue. Lazurite makes up 25% to 40% of lapis lazuli.

Did You Know?

• Most lapis lazuli gets its blue color from Hauyne, and almost none contain true lazurite; this was changed in 2021 when lazurite was redefined so that only a quarter (instead of half) of the cages need contain sulfide.
• Lazurite and hauyne appear to have the same structure and both are sulfate-dominant minerals.
• The difference between lazurite and hauyne may be a consequence of the redox state, specifically the sulfate to sulfide ratio.