Granite

Hardness: 6-7 on Mohs scale (due to quartz and feldspar). Color: Highly variable, but commonly pink, red, gray, or white, with dark mineral specks. Luster: Vitreous to dull. Crystal Structure: Phaneritic (coarse-grained) texture, meaning individual mineral grains are large enough to be seen with the naked eye. Cleavage: Present in feldspar and biotite components. Specific Gravity: 2.6-2.7 g/cm³.

Formation Process: Granite is an intrusive (plutonic) igneous rock, meaning it forms from the slow crystallization of magma beneath Earth's surface. The slow cooling allows large crystals to form. Geological Age: Granites can form at various geological ages, from the Precambrian to relatively recent geological periods, whenever magma intrusions occur in continental crust. Environments: Forms deep within the crust during processes like mountain building (orogeny) or continental rifting.

Industry/Construction: Extremely important as a construction material (dimension stone) for countertops, floor tiles, paving stones, building facades, and monuments due to its durability, strength, and aesthetic appeal. Jewelry/Collecting: While not typically used in fine jewelry itself, granite is sometimes polished for ornamental objects. Collectors value well-formed specimens for their mineral composition and textural features.

Granite is named from the Latin word 'granum' for 'grain', in reference to its coarse-grained structure. It is one of the most abundant intrusive igneous rocks in Earth's continental crust and forms the core of many mountain ranges. Large granite intrusions are called batholiths. The oldest known rocks on Earth are granitic in composition, dating back over 4 billion years.

How to Identify in the Field: Look for its coarse-grained (phaneritic) texture, indicating slow cooling. The presence of visible grains of quartz (glassy, clear/gray), feldspar (pink, white, or off-white), and dark minerals (biotite mica, hornblende) is characteristic. It is generally hard and resistant to weathering. Common Locations Found: Granite is found globally in continental shield areas, mountain ranges, and large igneous provinces. Major occurrences include the Sierra Nevada Batholith in California, the Rocky Mountains, the Appalachian Mountains, parts of Scandinavia, and many other cratonic regions. Tips for Collectors: Look for freshly broken surfaces to best observe the mineral grains and color. Note the relative proportions of light and dark minerals, which can indicate variations in composition. Be aware that 'granite' in commercial use can sometimes refer to other similar-looking felsic igneous or metamorphic rocks.