igneous
Basalt Pebble
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8 to 3.0
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8 to 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been rounded by fluvial or marine erosion.
Uses & applications
Used in construction as crushed stone, road base, or concrete aggregate. Polished versions are used in hot stone massage and decorative landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible crystals. Commonly found on volcanic beaches, riverbeds near volcanic activity, and oceanic islands like Hawaii.
More like this
Other igneous specimens
Blue Apatite
Fluorapatite (Ca5(PO4)3F)
mineral
Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
Igneous
Magnetite
Iron(II,III) oxide (Fe3O4)
mineral
Blue Apatite
Apatite (Group), Ca5(PO4)3(F,Cl,OH)
mineral
Sodalite
Sodalite - Na8(Al6Si6O24)Cl2
mineral
Magnetite
Magnetite (Fe3O4)
mineral