Ultramarine (lazurite type) Na₈(Al₆Si₆O₂₄)S₂

Unit cell

Lattice constants

a = 9.060 Å, b = 9.060 Å, c = 9.060 Å; α = 90°, β = 90°, γ = 90°

Cell volume

743.7 ų

Atoms in the cell

46 (Na 8, Al 6, Si 6, O 24, S 2)

Formula units Z

1

Calculated density

1.77 g cm⁻³

Shortest contact

1.562 Å

Coordination

Na

CN 6 at 2.53 Å (6 O)

Al

CN 4 at 1.70 Å (4 O)

Si

CN 4 at 1.56 Å (4 O)

O

CN 2 at 1.56 Å (1 Si + 1 Al)

S

CN 4 at 3.41 Å (4 Na)

About the structure

• The sodalite framework (compare sodalite in this lab) with polysulfide radicals instead of chloride in the cages; the S drawn at the cage centre is the average position of the S₃⁻ group.
• The S₃⁻ radical anion absorbs at about 600 nm and gives the deep blue of lapis lazuli and of synthetic ultramarine, made since 1828 from clay, soda and sulfur.
• Coordinates from the Crystallography Open Database, entry 1010316 (open data); hydrogen and water sites with partial occupancy below 0.5 are left out. Some sites are partially occupied in the real crystal.

Atom positions (fractional, one cell)

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