igneous

Granite Pebble

Granite; primarily composed of Quartz (SiO2), Feldspar (KAlSi3O8), and Mica

Hardness: 6-7 on Mohs scale. Color: Speckled white, grey, and black. Luster: Dull to vitreous. Structure: Phaneritic (coarsegrained, visible crystals) though water-worn in this specimen. Specific gravity: 2.63 - 2.75.

Hardness: 6-7 on Mohs scale
Color: Speckled white, grey, and black
Luster: Dull to vitreous

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. This specific specimen has been shaped and smoothed by fluvial or coastal abrasion over hundreds to thousands of years.

Uses & applications

Used in construction as crushed stone or gravel, high-end countertops when in slab form, and as decorative landscaping stones.

Geological facts

Granite makes up a large portion of the Earth's continental crust. It is one of the hardest natural stones, making it the preferred material for monuments like Mt. Rushmore.

Field identification & locations

Identify by its 'salt and pepper' speckled appearance and high hardness (it will easily scratch glass). Common in riverbeds, glacial deposits, and mountain ranges worldwide.

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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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