Igneous Rock

Granite

Granite (a felsic intrusive igneous rock)

Hardness: 6-7 on Mohs scale

Identified July 26, 2025More igneous rock →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Typically light-colored, with shades of white, gray, pink, or red, due to the feldspar and quartz content. The dark specks are often biotite mica or hornblende. Luster: Vitreous to greasy for quartz, pearly for feldspar, and glassy/resinous for other minerals. Crystal Structure: Granitic rocks are phaneritic (coarse-grained) meaning individual crystals are visible to the naked eye. Grains are interlocking. Cleavage: Quartz has no cleavage; feldspar has two directions of cleavage; micas have one perfect basal cleavage. Specific Gravity: Typically 2.65 - 2.75.

Formation & geological history

Granite forms from the slow crystallization of magma below the Earth's surface. It's an intrusive igneous rock, meaning it solidifies deep within the crust. The slow cooling allows for the formation of large, interlocking mineral grains. It forms in continental collision zones or during processes of crustal thickening and magmatic differentiation. Its geological age varies widely, ranging from Precambrian to relatively recent Cenozoic formations, depending on the specific intrusion event.

Uses & applications

Industry/Construction: Widely used as a construction material for building facades, paving, flooring, curbing, and monumental stonework due to its hardness, durability, and aesthetic appeal. Countertops: Popular for kitchen countertops and backsplashes due to its scratch and heat resistance. Jewelry/Decorative: Polished granite slabs are used for decorative purposes, and sometimes smaller pieces are tumbled for craft or ornamental use.

Geological facts

Granite is one of the most abundant intrusive igneous rocks in the Earth's continental crust. Its name comes from the Latin word 'granum', meaning 'grain', referring to its coarse-grained structure. Monument Valley, Yosemite Valley, and Mount Rushmore are famous geological features and monuments carved from different types of granite. It's often associated with mountainous regions and major continental landmasses.

Field identification & locations

In the field, granite is identified by its coarse-grained texture and speckled appearance, showing visible interlocking crystals of light-colored quartz and feldspar, along with darker minerals like biotite or hornblende. It's a very hard rock, difficult to scratch with a knife. Common locations include mountainous regions and continental shields worldwide, such as the Sierra Nevada Batholith in California, the Rocky Mountains, the Appalachian Mountains, and areas of Scandinavia, Brazil, and India. For collectors, granite specimens are common, but exceptional polished slabs or unique mineral inclusions can be sought after.

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Felsic Igneous Rock (likely Rhyolite or weathered Granite)

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