Granite

Hardness: 6-7 (Mohs scale); Color: Variable, commonly white, pink, gray, or black, depending on mineral composition. The sample appears light gray with darker inclusions. Luster: Vitreous to dull in weathered samples. Crystal Structure: Phaneritic (coarse-grained) with interlocking crystals. Cleavage: Minerals within granite (like feldspar and mica) have cleavage, but the rock itself does not. Specific Gravity: 2.6 – 2.7 g/cm³.

Formation Process: Granitic rocks form from the slow crystallization of magma deep beneath Earth's surface (intrusive igneous rock). As magma cools slowly, large interlocking crystals have time to grow. Geological Age: Granites can be found in rocks from all geological ages, from Precambrian to Cenozoic, commonly associated with continental crust and mountain-building events. Environments: Formed in batholiths, stocks, and dikes in continental collision zones and subduction zones.

Industry: Widely used as building stone for countertops, flooring, curbing, gravestones, and dimension stone due to its durability and aesthetic appeal. Construction: Crushed granite is used as aggregate in road building and concrete. Jewelry: Not typically used in jewelry due to its opaque nature, but polished granite can be used for ornamental purposes.

Granite is one of the most abundant intrusive igneous rocks in the Earth's continental crust. It is often associated with the formation of mountain ranges. The varying colors in granite are due to different proportions of its mineral components.

How to Identify in the Field: Look for its coarse-grained texture (phaneritic), interlocking crystals that are visible to the naked eye. The presence of quartz (glassy, anhedral), feldspar (blocky, white to pink), and mica (shiny, flaky, dark biotite or light muscovite) are key indicators. Its overall light color (felsic) is also characteristic. Common Locations Found: Found globally in mountainous regions, shield areas, and continental interiors where ancient igneous activity occurred. Examples include the Sierra Nevada Batholith (USA), Scottish Highlands (UK), and parts of the Canadian Shield. Tips for Collectors: Look for freshly broken surfaces to observe true crystal shapes and colors. Note the proportion of different minerals to help identify variations in granite (e.g., granodiorite, diorite).