Granite

Hardness: 6-7 on Mohs scale. Color: Highly variable, commonly white, pink, grey, or black, often with a speckled appearance due to a mix of minerals. Luster: Vitreous to glassy for quartz and feldspar, dull to sub-metallic for micas and amphiboles. Crystal structure: Phaneritic (coarse-grained) with interlocking crystals. Cleavage: Feldspar exhibits good cleavage in two directions at nearly 90 degrees; mica has perfect basal cleavage. Specific gravity: 2.6-2.7 g/cm³.

Formation process: Granite is an intrusive igneous rock, meaning it forms from the slow crystallization of magma below the Earth's surface. The slow cooling allows for the growth of large, visible mineral crystals. Geological age: Granites can be found from the Precambrian era (over 540 million years ago) to relatively recent geological times, forming as a result of various orogenic (mountain-building) events and magmatic intrusions in continental crust.

Industry/Construction: Widely used as a building material for dimension stone (countertops, floor tiles, paving stones, curbing), facing stone for buildings, monument stone, and crushed stone for road aggregate and railway ballast. Jewelry: Not typically used as a gemstone, but polished slabs can be used in decorative items and inlay. Due to its durability and aesthetic appeal, it is highly valued for architectural and decorative purposes.

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 the Earth's continental crust. Many mountain ranges and large batholiths are composed of granite. It has been used for millennia in construction, from ancient Egyptian pyramids to modern skyscrapers.

How to identify in the field: Look for its phaneritic (coarse-grained) texture, where individual mineral crystals (quartz, feldspar, mica, amphibole) are clearly visible to the naked eye. The color variation, from light to dark, is also a key indicator. It often forms large, massive outcrops or boulders due to its resistance to weathering. Where it's commonly found: Granite is found worldwide in continental crust, often in old shield areas, mountain ranges, and as the core of continents. Major occurrences include the Sierra Nevada Batholith in California, the Rocky Mountains, the Appalachian Mountains, the Scottish Highlands, Scandinavia, and many parts of Asia and Africa. Tips for collectors: Granite is very common, so focus on collecting samples that display interesting mineral compositions, unique textures, or characteristic weathering patterns (like spheroidal weathering).