igneous

Granite (River Pebble)

Phaneritic intrusive igneous rock (Felsic)

Hardness: 6-7 Mohs; Color: Mottled tan, cream, and dark grey/black; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals of quartz, feldspar, and mica); Specific gravity: 2.6-2.7.

Hardness: 6-7 Mohs
Color: Mottled tan, cream, and dark grey/black
Luster: Dull to vitreous

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground, typically within the Earth's continental crust. This specimen has been rounded and smoothed by water erosion in a river or stream environment.

Uses & applications

Large-scale construction, countertops, monuments, and decorative gravel. Small pebbles like this are used in landscaping or as aquarium decor.

Geological facts

Granite is the most common igneous rock found on Earth's continents. The pinkish-tan color in this specimen likely comes from potassium feldspar (orthoclase).

Field identification & locations

Identify by the 'salt and pepper' appearance of interlocking mineral grains and its high hardness (it will scratch glass). Commonly found in mountain ranges and riverbeds downstream from granitic plutons.

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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

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Iron(II,III) oxide (Fe3O4)

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Magnetite

Magnetite (Fe3O4)

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