Egyptian blue (cuprorivaite) CaCuSi₄O₁₀

Unit cell

Lattice constants

a = 7.302 Å, b = 7.302 Å, c = 15.130 Å; α = 90°, β = 90°, γ = 90°

Cell volume

806.7 ų

Atoms in the cell

64 (Ca 4, Cu 4, Si 16, O 40)

Formula units Z

4

Calculated density

2.17 g cm⁻³

Shortest contact

1.589 Å

Coordination

Ca

CN 8 at 2.37 Å (8 O)

Cu

CN 4 at 1.93 Å (4 O)

Si

CN 4 at 1.59 Å (4 O)

O

CN 2 at 1.60 Å (1.6 Si)

About the structure

• Sheets of corner-sharing SiO₄ tetrahedra enclose square-planar CuO₄ units; the Cu²⁺ in this square environment gives the pigment its colour (and its near-infrared luminescence).
• The oldest synthetic pigment, made in Egypt from about 3000 BCE by heating sand, lime and copper.
• Ca²⁺ sits between the silicate sheets in 8-coordination.
• Coordinates from the Crystallography Open Database, entry 9009762 (open data); hydrogen and water sites with partial occupancy below 0.5 are left out.

Atom positions (fractional, one cell)

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