Vaterite, CaCO3, is classified as a vaterite Group Carbonate. A calcium carbonate mineral with a formula unit identical to — and thus a polymorph of — calcite, vaterite has an orthorhombic crystal system (Calcite forms trigonal crystals) and a pseudocubic crystal habit. vaterite’s structure consists of triangular carbonate ion groups (CO3), with a carbon at the center of the triangle and the three oxygens at each corner.