igneous

Granite Pebble

Phaneritic Felsic Igneous Rock (Granite)

Hardness: 6-7 Mohs; Color: Mottled pink, black, and gray; Luster: Dull to vitreous; Crystal structure: Phaneritic (large visible crystal grains of quartz, feldspar, and mica); Cleavage: Dependent on mineral (poor for quartz, two at 90 deg for feldspar); Specific gravity: 2.63-2.75

Hardness: 6-7 Mohs
Color: Mottled pink, black, and gray
Luster: Dull to vitreous

Identified May 31, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface (intrusive). This specimen specifically has been rounded by fluvial (water) or glacial erosion into a pebble.

Uses & applications

Commonly used in large scale for construction, countertops, and monuments; as a small pebble, it is used for landscaping, decorative aquariums, and teaching petrology.

Geological facts

Granite makes up the majority of Earth's continental crust. The pink color in this specimen is likely due to potassium feldspar (orthoclase), while the dark spots are biotite mica or hornblende.

Field identification & locations

Identify by looking for a 'salt and pepper' or mottled appearance with visible interlocking crystals. It is extremely common in areas with exposed batholiths or glacial till. Pebbles like this are easily found in riverbeds or gravel pits.

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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