igneous

Granite with Biotite and Quartz

Phaneritic Felsic Igneous Rock (composed of SiO2, KAlSi3O8, and K(Mg,Fe)3AlSi3O10(OH)2)

Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper appearance with white/grey quartz and black biotite; Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained, visible crystals); Cleavage: Perfect in biotite flakes, none in quartz.

Hardness: 6-7 (Mohs scale)
Luster: Vitreous to pearly

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silica-rich magma deep within the Earth's crust (intrusive cooling). These rocks can date back to several billion years (Precambrian) or be as young as a few million years depending on the tectonic setting.

Uses & applications

Used extensively in construction for countertops, floor tiles, and paving stones. High-quality specimens with large crystals are popular for geological teaching collections.

Geological facts

Granite makes up the majority of the Earth's continental crust. Its durability and resistance to weathering are why it is frequently used for public monuments and Egyptian obelisks.

Field identification & locations

Identify in the field by looking for a coarse-grained texture where individual mineral grains are visible to the naked eye. It is commonly found in mountain ranges and continental shields (e.g., the Rockies or the Appalachians). Collectors should look for distinct crystalline boundaries.

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