igneous
Black Beach Pebble / Basalt Pebble
Basalt / Mafic Volcanic Rock
Mohs hardness 5.5-6. Dark black to charcoal grey, fine-grained (aphanitic) texture, dull to sub-vitreous luster when wet, highly rounded and smoothed by wave erosion.
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Physical properties
Mohs hardness 5.5-6. Dark black to charcoal grey, fine-grained (aphanitic) texture, dull to sub-vitreous luster when wet, highly rounded and smoothed by wave erosion.
Formation & geological history
Formed from the rapid cooling of mafic lava rich in iron and magnesium at or near the Earth's surface, later eroded and rounded by ocean or river currents on volcanic beaches.
Uses & applications
Used for landscaping, decorative aquariums, beach stone jewelry, hand therapy/massage stones, and general rock collecting.
Geological facts
Black sand and black pebbles are characteristic of volcanic coastlines like those in Hawaii, Iceland, New Zealand, and Costa Rica.
Field identification & locations
Identified by its deep black color, smooth water-worn surface, high density, and lack of visible large mineral grains.
