Strontianite is a carbonate mineral, strontium carbonate (SrCO3). It has orthorhombic system, hexagonal twinned crystals, and it also occurs as massive or columnar aggregates. It can be pale green, white, gray, yellow, or brown. Strontianite is found in low-temperature hydrothermal veins, often in limestone. Hardness 3.5–4; relative density 3.7.