igneous

Amygdaloidal Basalt

Basalt with secondary mineral infilling

Hardness: 5-6 (matrix); Color: dark gray to greenish-black; Luster: dull to earthy; Texture: Vesicular (pitted) to amygdaloidal (filled pits); Structure: Fine-grained aphanitic matrix.

Hardness: 5-6 (matrix)
Color: dark gray to greenish-black
Luster: dull to earthy

Identified April 5, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 5-6 (matrix); Color: dark gray to greenish-black; Luster: dull to earthy; Texture: Vesicular (pitted) to amygdaloidal (filled pits); Structure: Fine-grained aphanitic matrix.

Formation & geological history

Formed from the rapid cooling of basaltic lava. The holes (vesicles) are created by trapped gas bubbles during eruption. If these holes later fill with minerals like quartz, calcite, or zeolites due to groundwater infiltration, it is called 'amygdaloidal'.

Uses & applications

Common basalt is used in construction as crushed stone for roads and railroads. Polished specimens are used as decorative stones or for educational geological collections.

Geological facts

Many of the world's finest copper and agate specimens are found within the amygdaloidal cavities of ancient basaltic lava flows, such as those in the Lake Superior region.

Field identification & locations

Identify in the field by its dark color, heavy weight (high specific gravity), and the presence of small rounded cavities or white/colored mineral 'spots' (amygdules) within a dense matrix.

Other igneous specimens

See all

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral