igneous
Kimberlite with Diamonds
Kimberlite (ultramafic potassic igneous rock)
Hardness (matrix): 4-6, (diamonds): 10. Color: Dark grey, greenish-black, or bluish-grey (Blue Ground). Luster: Dull to greasy. Crystal structure: Porphyritic. Specific gravity: 2.7-3.3.
- Color
- Dark grey, greenish-black, or bluish-grey (Blue Ground)
- Luster
- Dull to greasy
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Physical properties
Hardness (matrix): 4-6, (diamonds): 10. Color: Dark grey, greenish-black, or bluish-grey (Blue Ground). Luster: Dull to greasy. Crystal structure: Porphyritic. Specific gravity: 2.7-3.3.
Formation & geological history
Formed deep within the Earth's mantle (150-450 km) and transported to the surface by rapid, explosive volcanic eruptions through pipes or dikes. Diamonds are xenocrysts formed at high pressure millions to billions of years ago.
Uses & applications
Primary source for mining natural diamonds for both industrial cutting tools and jewelry.
Geological facts
Named after the town of Kimberley in South Africa. Only about 1 in 100 kimberlite pipes contain high-grade diamond concentrations.
Field identification & locations
Identify by its 'soapy' feel when weathered and presence of indicator minerals like pyrope garnet or chromium diopside. Found in ancient continental cratons in South Africa, Russia, Canada, and Australia.
