igneous

Scoria (Lava Rock)

Scoria (Vesicular Basalt)

Hardness: 5-6 Mohs; Color: reddish-brown, dark red, or black; Luster: dull/earthy; Crystal Structure: aphanitic (fine-grained) with large vesicles; Specific Gravity: 2.5-3.0 (but low bulk density due to air pockets)

Hardness: 5-6 Mohs
Color: reddish-brown, dark red, or black
Luster: dull/earthy

Identified March 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the cooling of mafic lava (high in iron and magnesium) that contains high amounts of dissolved gases. As the lava is ejected during volcanic activity, gas bubbles expand and become trapped as the rock solidifies, creating a vesicular texture.

Uses & applications

Commonly used in landscaping (lava rocks), as a lightweight aggregate in concrete, for high-temperature insulation, and in sauna heaters. It is also used in traction control on icy roads.

Geological facts

Unlike pumice, which is also a volcanic rock with holes, scoria has larger vesicles and thicker cell walls, which causes it to sink in water whereas pumice usually floats.

Field identification & locations

Identify in the field by its distinctive 'swiss cheese' or honeycomb texture and relatively low weight compared to solid basalt. Often found in volcanic cinder cones in places like the American Southwest, Iceland, and Italy.

Other igneous specimens

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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