Spar (mineralogy)
Spar is an old term in mining and mineralogy for crystals with obvious, easily visible faces. These crystals tend to break or cleave into rhomboidal, cubic, or layered pieces, and they usually have smooth, shiny surfaces. The word comes from miners and alchemists who used spar for nonmetallic minerals like gypsum; in Old English it was spærstān, meaning “spear stone,” a reference to their pointed crystal faces. Today, spar is often used more generally for bright, crystalline minerals.
Most commonly, spar describes easy-to-cleave, light-colored nonmetallic minerals such as feldspar, calcite, or baryte. Baryte (BaSO4), the main source of barium, is sometimes called heavy spar (from the Greek barys, “heavy”). Calcite often forms dogtooth spar crystals in vugs and caves.
Spar usually forms underwater, in the phreatic zone or below the water table, or in standing pools (pool spar). When a cave floods and pools form, submerged stalactites can evolve into bottlebrush-like formations. Minerals dissolved in water are deposited over long periods as calcite, gypsum, and sometimes halite, quartz, or fluorite, building up layers.
Spar can also form in air, from solutions seeping through cave walls or porous sediments. Air-grown spar is often gypsum or selenite, and it can appear as small needles in sediments or on the tips of gypsum chandeliers.
This page was last edited on 3 February 2026, at 07:14 (CET).