igneous

Basalt with Epidote (Greenstone)

Amygdaloidal Basalt (Ca2(Al, Fe)3(SiO4)3(OH) inclusions)

Hardness: 6-7 (Mohs). Color: Dark greyish-green to hunter green with small vesicles or patches. Luster: Dull/earthy (weathered) to vitreous (minerals). Structure: Aphanitic with porphyritic amygdules. Specific gravity: 2.8–3.0.

Hardness: 6-7 (Mohs)
Luster: Dull/earthy (weathered) to vitreous (minerals)

Identified March 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapid cooling of magnesium-rich and iron-rich lava at the surface. The green tint is often due to low-grade metamorphism (greenschist facies) where minerals like chlorite and epidote replace original mafic minerals.

Uses & applications

Commonly used in construction as crushed stone or aggregate. High-quality greenstone specimens are used in lapidary work for cabochons, polished river stones, and decorative landscaping.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. When weathered by water, it often gains a characteristic rounded shape and a smooth, almost 'waxy' feel if rich in fine-grained silica.

Field identification & locations

Identify by its heavy weight relative to its size and its dark, greenish-black hue. Found often on beaches near volcanic coastlines (Pacific Northwest, Great Lakes). Collectors should look for 'amygdules' (filled gas bubbles) that may contain quartz or agate.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral