igneous

Granite Pebble (River Rock)

Granite (composed primarily of Quartz, Feldspar, and Mica)

Hardness: 6-7 on Mohs scale; Color: Mottled gray, white, and brown; Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained internally, though surface is water-worn); Specific Gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: Mottled gray, white, and brown
Luster: Dull to vitreous

Identified April 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface. This specific specimen has been further shaped by fluvial (river) erosion, rounding its edges over thousands of years.

Uses & applications

River rocks of this type are used extensively in landscaping, drainage systems, construction aggregate, and as decorative elements in gardens.

Geological facts

Granite is the most common igneous rock found on Earth's continents. The mottling seen here is due to the different mineral crystals (Quartz, Feldspar, and Biotite) cooling at different rates.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and extreme hardness (it will scratch glass). Commonly found in riverbeds, glacial tills, and mountainous regions.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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