igneous

Basalt with Epidote

Mafic volcanic rock with Epidote (Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH))

Hardness: 5-7 (Mohs scale); Color: Gray-black with greenish patches; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained) with secondary monoclinic coatings; Specific Gravity: 2.8-3.3

Hardness: 5-7 (Mohs scale)
Color: Gray-black with greenish patches
Luster: Dull to vitreous

Identified May 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava. The greenish tint indicates hydrothermal alteration where epidote replaces original minerals like plagioclase or pyroxene.

Uses & applications

Commonly used as crushed stone for road base, concrete aggregate, and railroad ballast. Decorative specimens are used in landscaping or small mineral collections.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor; epidote is often a sign of low-grade metamorphism.

Field identification & locations

Identify by its dark core, fine grain, and weight. Greenish surfaces that don't scrub off are usually the epidote mineral. Found globally in volcanic regions like the Pacific Northwest or Iceland.

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

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