igneous

Andesite

Andesite (contains Plagioclase feldspar, Pyroxene, Hornblende)

Hardness: 6-7 (Mohs); Color: Dark gray to greenish-gray with visible lighter phenocrysts; Luster: Dull/Earthy (matrix) to Vitreous (crystals); Structure: Porphyritic/Aphanitic; Specific Gravity: 2.4-2.8

Hardness: 6-7 (Mohs)
Color: Dark gray to greenish-gray with visible lighter phenocrysts
Luster: Dull/Earthy (matrix) to Vitreous (crystals)

Identified May 20, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the cooling of intermediate volcanic lava at the Earth's surface, typically at subduction zones above convergent plate boundaries. Most specimens range from Cenozoic to recent times.

Uses & applications

Used primarily in construction for crushed stone, road base, and aggregate. Also used as dimension stone for tiles and landscape decoration.

Geological facts

Andesite is the second most common volcanic rock in the Earth's crust after basalt. It is named after the Andes Mountains, where it is found in great abundance.

Field identification & locations

Identify by its 'salt and pepper' appearance (white plagioclase crystals in a dark matrix) and its intermediate density. Commonly found in volcanic mountain ranges like the Cascades or Andes. Use a hand lens to see small grain textures.

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

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