Granite

Hardness: 6-7 (Mohs scale) due to quartz and feldspar content. Color: Typically light-colored, ranging from white, gray, to pink or reddish, often with darker specks (biotite, hornblende). Luster: Vitreous to dull. Crystal Structure: Phaneritic (coarse-grained) with interlocking crystals visible to the naked eye. No obvious cleavage planes as a rock, though individual mineral components have cleavage (e.g., feldspar). Specific Gravity: 2.6 – 2.7 g/cm³.

Formed from the slow crystallization of magma far below Earth's surface (intrusive igneous rock). This slow cooling allows for the formation of large, interlocking mineral grains. Geological Age: Granites are found throughout Earth's history, from Precambrian shields (billions of years old) to relatively young Tertiary intrusions (tens of millions of years old). Commonly formed in continental collision zones or during episodes of crustal thickening, where magma is generated by partial melting of continental crust.

Industry: Widely used as a construction material for building facades, paving, curbing, and monumental stonework due to its durability and aesthetic appeal. Jewelry: While not a gemstone itself, polished granite is often used in decorative items and countertops. Construction: Primary material for kitchen countertops, flooring, and wall cladding; excellent for outdoor applications due to weather resistance.

Granite is one of the most abundant igneous rocks in the Earth's continental crust. Mount Rushmore in South Dakota, USA, is carved into a massive granite batholith. "Granite" is often used commercially for any light-colored, large-grained igneous rock, which can include granodiorite, diorite, and anorthosite.

How to identify in the field: Look for its speckled appearance with visible interlocking grains of different minerals (typically white/pink feldspar, gray/smoky quartz, and black biotite/hornblende). It feels rough to the touch due to the coarse texture. Compare its hardness by trying to scratch it with steel (it shouldn't scratch easily). Common locations: Found globally in continental crust, particularly in mountain ranges, ancient shields (like the Canadian Shield, Baltic Shield), and large intrusive bodies called batholiths. Tips for collectors: Collect fresh, unweathered samples if possible. Note relative proportions of different minerals to help distinguish it from similar rocks like granodiorite or diorite.