metamorphic
Lapis Lazuli (prominent blue specimen in collection)
Lazurite-rich metamorphic rock (Na,Ca)8(AlSiO4)6(SO4,S,Cl,OH)2
Hardness: 5-5.5 (Mohs scale), Color: Intense celestial blue, Luster: Vitreous to greasy, Crystal structure: Isometric (dodecahedral crystals are rare), Cleavage: Imperfect, Specific gravity: 2.7–2.9
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Intense celestial blue, Luster: Vitreous to greasy, Crystal structure: Isometric (dodecahedral crystals are rare), Cleavage: Imperfect, Specific gravity: 2.7–2.9
Formation & geological history
Formed through contact metamorphism of limestone or marble; typically found in blocks within crystalline marble. Geological age varies by deposit, ranging from 60 million to over 2 billion years.
Uses & applications
Used primarily in jewelry (cabochons, beads), decorative carvings, pigments (ultramarine), and as architectural inlay and historical sculptures.
Geological facts
Lapis lazuli has been mined for over 6,000 years, primarily in the Sar-i Sang mines of Afghanistan. It was the source of the most expensive pigment in the Renaissance, used by painters like Vermeer and Michelangelo.
Field identification & locations
Identify by its distinct 'royal blue' color often accompanied by gold-colored pyrite inclusions and white calcite veining. Found in Afghanistan, Chile, Russia, and Canada. Test by checking for evenness of color and checking against a porcelain streak plate (white streak).
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