igneous

Granite Cobble

Phaneritic Felsic Igneous Rock

Hardness: 6-7 on Mohs scale. Color: Mottled grey, white, and black. Luster: Dull to vitreous. Crystal structure: Phaneritic (visible coarse-grained crystals). Cleavage: Imperfect. Specific Gravity: 2.63 to 2.75.

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

Identified May 24, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. High in silica and alkali metal oxides. This specific specimen shows rounding from water erosion (alluvial or glacial transport).

Uses & applications

Used in construction, aggregate, landscaping, and as a decorative garden stone. Granite is also a major source of dimension stone for countertops and monuments.

Geological facts

Granite makes up a large portion of the continental crust. Because of its hardness, it survives long journeys in rivers, which is why it is often found as smooth cobbles far from its original mountain source.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals of quartz and feldspar. Found globally in mountainous regions or riverbeds downstream from crystalline basements.

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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