igneous

Granite Pebble

Granite (Phaneritic intrusive igneous rock)

Hardness: 6-7 (Mohs scale); Color: speckled gray, white, and black; Luster: Vitreous to dull; Crystal structure: Coarse-grained (phaneritic); Cleavage: Perfect on feldspar grains; Specific gravity: 2.63 to 2.75

Hardness: 6-7 (Mohs scale)
Color: speckled gray, white, and black
Luster: Vitreous to dull

Identified May 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. These rocks are found in continental crust and are typically associated with mountain-building tectonic events involving various geological eras.

Uses & applications

Used in construction, monuments, countertops, and as road aggregate. Small pebbles are often used in landscaping or aquarium gravel.

Geological facts

Granite is the most common igneous rock found on Earth's continents. The name comes from the Latin 'granum', meaning a grain, in reference to its coarse-grained structure.

Field identification & locations

Identify by its 'salt and pepper' appearance caused by light-colored feldspar/quartz and dark biotite or hornblende. Commonly found in riverbeds or near mountain ranges.

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