By Yasmin Zinni, Updated Aug 30, 2022
Calcite and quartz are two of the most common minerals found in various rock types across the globe. While calcite dissolves readily in acidic solutions, quartz remains chemically inert under similar conditions. Though both are widespread, quartz is the planet’s second most abundant mineral, just after feldspar.
Calcite typically presents as white or translucent, though it can also appear green, gray, blue, or yellow. Quartz displays a broader spectrum of colors—from the pale yellow of citrine to the striking purple of amethyst. Both minerals crystallize in hexagonal and pyramidal forms, but calcite exhibits a greater variety of crystal habits.
Calcite’s chemical formula is CaCO₃, comprising calcium, carbon, and oxygen. Quartz, on the other hand, is SiO₂, consisting of silicon and oxygen. Quartz is significantly harder, scoring 7 on the Mohs scale, compared to calcite’s 3.
Calcite is a major component of sedimentary rocks such as limestone, as well as the stalagmites and stalactites that form in caves. It also contributes to shells of marine organisms like sponges and oysters. Quartz predominates in igneous rocks—granite and basalt—and metamorphic formations like quartzite and gneiss. It is not associated with living organisms.
Calcite’s softness and acidity‑neutralizing properties make it valuable in construction (cements and mortars) and in chemical/pharmaceutical applications to adjust pH levels in rivers, lakes, and soils. Quartz’s durability and optical qualities render it essential for glass manufacturing, industrial abrasives, and as a gemstone in jewelry.
