igneous

Granite Water-Worn Pebble

Felsic intrusive igneous rock (Granite)

Hardness: 6-7 Mohs; Color: Pink, white, and smoky grey/black; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals of quartz, feldspar, and mica); Cleavage: Indistinct in hand specimen.

Hardness: 6-7 Mohs
Color: Pink, white, and smoky grey/black
Luster: Dull to vitreous

Identified May 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of silica-rich magma deep underground. This specific specimen has been rounded and smoothed by water erosion in a river or beach environment. Ages vary from Precambrian to Cenozoic.

Uses & applications

Large-scale use in construction (countertops, monuments), aggregate for roads. Smaller pebbles like this are used in decorative landscaping, aquariums, and rock tumbling.

Geological facts

Granite makes up much of the Earth's continental crust. The pink color in this specimen is specifically due to the presence of Potassium Feldspar (Orthoclase).

Field identification & locations

Identify by the 'salt and pepper' appearance and visible interlocking crystals of different colors. It is harder than steel and will not be scratched by a knife. Commonly found in mountainous regions or glacial till.

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Magnetite

Magnetite (Fe3O4)

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