igneous

Granite Pebble

Granite (Phaneritic intrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: typically mottled grey, white, pink, or tan; Luster: vitreous to dull; Crystal structure: coarse-grained holocrystalline; Cleavage: none (irregular fracture); Specific gravity: 2.63 - 2.75

Hardness: 6-7 on Mohs scale
Color: typically mottled grey, white, pink, or tan
Luster: vitreous to dull

Identified March 18, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. Granite is part of the continental crust and can range in geological age from the Archean Eon to the Cenozoic Era, often revealed through tectonic uplift and erosion.

Uses & applications

Larger deposits are used for construction, countertops, monuments, and paving. Small pebbles are often used in landscaping, as road aggregate, or in concrete production.

Geological facts

Granite is the most common igneous rock found on Earth's continents and makes up the core of many mountain ranges. It is the rock that famously forms the climbing walls of Yosemite National Park (El Capitan).

Field identification & locations

Identify in the field by its 'salt and pepper' appearance caused by interlocking crystals of quartz, feldspar, and mica. It is found globally in continental crust/mountainous regions. Collectors look for unique color variations or large crystal 'porphyritic' textures.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

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