igneous
Kimberlite
Kimberlite
Hardness: 6-7 (matrix) though variable; Color: Dark grey, greenish-grey, or bluish-grey (Blue Ground); Luster: Dull to greasy; Structure: Porphyritic texture with large phenocrysts (megacrysts) in a fine-grained groundmass; Cleavage: None.
- Hardness
- 6-7 (matrix) though variable
- Color
- Dark grey, greenish-grey, or bluish-grey (Blue Ground)
- Luster
- Dull to greasy
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Physical properties
Hardness: 6-7 (matrix) though variable; Color: Dark grey, greenish-grey, or bluish-grey (Blue Ground); Luster: Dull to greasy; Structure: Porphyritic texture with large phenocrysts (megacrysts) in a fine-grained groundmass; Cleavage: None.
Formation & geological history
Formed from deep-mantle volcanic eruptions (at depths of 150-450 km) that travel rapidly to the surface in structures called pipes or diatremes. Most pipes formed between 70 and 150 million years ago, though some are much older.
Uses & applications
Primarily known as the main host rock for diamonds. It is also used as an indicator for mining exploration and occasionally for scientific research into the Earth's mantle composition.
Geological facts
Kimberlite is named after the town of Kimberley in South Africa, where a 83.5-carat diamond discovery in 1871 started a diamond rush. It is essentially a 'fossilized' volcanic pipe that brings deep-earth materials to the surface.
Field identification & locations
Identified by its porphyritic texture containing rounded crystals of olivine, phlogopite, and pyrope garnet in a dark, serpentinized matrix. Found in ancient continental cratons in South Africa, Russia, Canada, and the USA.
