igneous
Larvikite
Monzonite (intermediate intrusive igneous rock containing plagioclase, alkali feldspar, augite, and biotite)
Hardness: 6-6.5; Color: Dark grey, charcoal, or bluish-black; Luster: Vitreous to sub-metallic; Crystal Structure: Monoclinic; Cleavage: Good; Specific Gravity: 2.59–2.63. It is characterized by an internal iridescent blue/silver reflection known as the Schiller effect.
- Hardness
- 6-6
- Color
- Dark grey, charcoal, or bluish-black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 6-6.5; Color: Dark grey, charcoal, or bluish-black; Luster: Vitreous to sub-metallic; Crystal Structure: Monoclinic; Cleavage: Good; Specific Gravity: 2.59–2.63. It is characterized by an internal iridescent blue/silver reflection known as the Schiller effect.
Formation & geological history
Formed at great depths (plutonic) from the cooling of magma approximately 292–298 million years ago during the Permian period. It is specifically associated with the Oslo Rift in Norway.
Uses & applications
Used extensively in architecture for building facades (notably the United Nations building), kitchen countertops, and monument stones. It is also popular in jewelry as beads and cabochons due to its labradorescence.
Geological facts
Often misidentified as 'Black Moonstone' or 'Blue Pearl Granite.' It is the National Stone of Norway. Unlike true Granite, it contains little to no quartz.
Field identification & locations
Identify in the field by its distinctive 'labradorescence' or 'Schiller effect'—a flash of blue or silver light when the dark stone is rotated. Primary locations include the Larvik region in Norway. Collectors should look for high-contrast flashes of color against the dark matrix.
