Calcite CaCO₃

Unit cell

Lattice constants

a = 4.990 Å, b = 4.990 Å, c = 17.060 Å; α = 90°, β = 90°, γ = 120°

Cell volume

367.9 ų

Atoms in the cell

30 (Ca 6, C 6, O 18)

Formula units Z

6

Calculated density

2.71 g cm⁻³

Shortest contact

1.282 Å

Coordination

Ca

CN 6 at 2.36 Å (6 O)

C

CN 3 at 1.28 Å (3 O)

O

CN 1 at 1.28 Å (1 C)

About the structure

• A distorted rock-salt arrangement of Ca²⁺ and planar CO₃²⁻ ions, the carbonate planes all perpendicular to c.
• Coordination: Ca 6 (octahedral, by O of six different carbonates), C 3 (trigonal planar).
• MgCO₃ (magnesite), FeCO₃ (siderite), NaNO₃ share the structure; aragonite is the other CaCO₃ polymorph.

Atom positions (fractional, one cell)

Z, coordination numbers, distances, density and packing on this page are computed from these coordinates.