Granite

Hardness: 6-7 on Mohs scale (due to quartz and feldspar). Color: Ranges from pinks, reds, and grays to black and white, depending on mineral composition. Luster: Vitreous to sub-vitreous. Crystal Structure: Interlocking phaneritic (coarse-grained) crystals, typically without distinct crystal forms. Cleavage: Not applicable for the rock itself, but its constituent minerals (e.g., feldspar) have cleavage. Specific Gravity: 2.6-2.7 g/cm³.

Granite is an intrusive igneous rock, meaning it forms from the slow crystallization of magma below Earth's surface. This slow cooling allows for the formation of large, visible mineral grains. It typically forms in the core of mountain ranges during orogenic (mountain-building) events, often resulting from the subduction of oceanic crust beneath continental crust. Its geological age varies widely, from Precambrian (billions of years old) to relatively young Tertiary intrusions.

Industry: Widely used as crushed stone in construction for road building, railway ballast, and foundations. Construction: Popular as dimension stone for building facades, paving, flooring, countertops, and monuments due to its hardness, durability, and attractive appearance. Jewelry: Not typically used in jewelry itself, but some of its constituent minerals can be. However, polished granite is sometimes used for ornamental items. Collecting Value: Common and readily available, so individual specimens generally don't command high prices, but large, well-formed samples or unique varieties can be desirable.

Granite is one of the most common rocks in the Earth's continental crust. Mount Rushmore, the Half Dome in Yosemite National Park, and the base of many mountain ranges are all composed primarily of granite. It's often associated with mountainous regions and major tectonic plate collisions. The word 'granite' comes from the Latin 'granum', meaning 'grain', in reference to its coarse-grained structure.

To identify granite in the field, look for its coarse-grained texture and the presence of visible, interlocking crystals of quartz (usually clear to grayish), feldspar (often pink, white, or off-white), and mica (black biotite or silvery muscovite). The overall color is a good indicator, often being light with distinct darker flecks. It will feel hard and heavy. It's commonly found in continental shields, ancient cratons, and the cores of eroded mountain ranges worldwide. Good localities include the Sierra Nevada mountains in California, the Rocky Mountains, New England (USA), Scandinavia, and many parts of India and Brazil. For collectors, look for specimens with large, well-defined crystals and interesting color variations.