Granite

Hardness: 6-7 on Mohs scale. Color: Typically light grey to white, but can be pink, red, black, or green depending on mineral composition. Luster: Vitreous to sub-vitreous. Crystal Structure: Anhedral to euhedral interlocking grains, typically phaneritic (coarse-grained). Cleavage: Minerals within possess cleavage (e.g., feldspar, mica), but the rock itself does not. Specific Gravity: 2.6 – 2.7 g/cm³.

Granite forms from the slow crystallization of magma below Earth's surface (intrusive igneous). It is primarily formed from the cooling of felsic magma, rich in silica and alkali metals. This slow cooling allows for the formation of large, interlocking mineral grains. The geological age of granite can vary widely, from Precambrian (billions of years old) to relatively young, depending on the specific tectonic setting and magmatic activity.

Industry/Construction: Widely used as building stone for dimension stone (blocks, tiles, countertops, paving), aggregate (crushed stone for roads, concrete), and monumental stone (sculptures, memorials). Jewelry: Not used as a gemstone itself, but polished granite is often used for decorative purposes, such as inlays or as a base for jewelry displays. Its durability and aesthetic appeal make it a popular choice for architectural finishes.

Granite is one of the most common intrusive igneous rocks and forms the core of many mountain ranges. Its name comes from the Latin 'granum', meaning 'grain', in reference to its coarse-grained structure. It has been used in construction for thousands of years, with notable examples including ancient Egyptian temples and modern skyscrapers. The term 'granite' is often used loosely in commercial terms to include other coarse-grained igneous rocks like granodiorite or syenite.

Field Identification: Observe its phaneritic (coarse-grained) texture, where individual mineral grains (like white/pink feldspar, grey glassy quartz, black mica) are visible to the naked eye. It feels hard and rough due to its interlocking crystal structure. Look for variations in color based on the dominant feldspar and accessory minerals. Common Locations: Found in continental crust, particularly in orogenic belts (mountain ranges) and cratonic shields. Major granitic intrusions are found globally, including in the Sierra Nevada Batholith (USA), Scottish Highlands (UK), and parts of Scandinavia, South America, and Africa. Tips for Collectors: Granite specimens are common and collected for educational purposes or for their aesthetic qualities when polished. Look for areas with exposed bedrock, road cuts, or riverbeds where granite is naturally weathered and exposed.