igneous
Black basalt pebble
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectFine-grained, dark gray to black, usually dull to slightly vitreous; hardness about 6, massive with no visible cleavage, and specific gravity roughly 2.8–3.0. The smooth oval shape indicates water tumbling or deliberate polishing; pale specks may be feldspar or weathering products.
Identified More igneous →
Explore Black basalt pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, dark gray to black, usually dull to slightly vitreous; hardness about 6, massive with no visible cleavage, and specific gravity roughly 2.8–3.0. The smooth oval shape indicates water tumbling or deliberate polishing; pale specks may be feldspar or weathering products.
Formation & geological history
An extrusive mafic igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly from volcanic flows or oceanic crust. Basalt ranges from Precambrian to modern in age; this specimen’s exact age cannot be determined visually.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, building stone, and landscaping material; polished pieces are sold as inexpensive decorative stones. Typical loose collector value is about $1–$10.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the ocean floor. Its dark color reflects abundant ferromagnesian minerals, while rapid cooling prevents large crystals from developing.
Field identification & locations
Likely basalt if it is opaque, dense, fine-grained, and leaves a gray streak rather than a glassy one; a magnet may show weak attraction if iron-rich. Common worldwide, especially volcanic regions, river gravels, and beaches; identification from a photograph is not definitive.
