Celestine
- named from the Latin word caelestis meaning celestial, which in turn is derived from the Latin word caelum meaning sky or heaven because of its often soft blue color
- pure Celestine is colourless
- due to lattice defects in Celestine, colour centres are created which give the crystal its characteristic bluish colour
- these centers are often additionally stabilized by the presence of pottasium ions
- heating to over 200 °C “cures” these lattice defects and the mineral loses its color
- radiation with X-rays creates new or more lattice defects and the color returns or can be intensified.
- Formula: SrSO4
- Space group: Pnma (No. 62)
- Crystal system: orthorhombic
- Crystal class: mmm
- Lattice parameters: a = 8.360 Å, b = 5.352 Å, c = 6.858 Å, α = β = γ = 90°
Picture: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
Crystal structure (click on the pictures to download the VESTA file):
(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).)
- SO4 tetrahedra (yellow)
- SrO8 polyhedra (green)
- Oxygen (red)
For a 3D interactive version, see here:
The Fascination of Crystals and Symmetry 