Celestine
SrSO4
Celestine is a sulfate mineral prized by collectors for its exceptional color range, with notable Chinese occurrences.
Celestine — also called celestite — is strontium sulfate and the chief ore of strontium. Collectors prize it above all for its soft sky-blue colour, the inspiration for its name (from the Latin caelestis, 'heavenly'), seen at its finest in the crystal-lined geodes of Madagascar.
Identifying celestine
Celestine is moderately soft (3–3.5), with tabular or prismatic crystals, a glassy lustre and colours from pale sky-blue to white, grey and pale orange. It closely resembles barite but is lighter and contains strontium rather than barium — strontium gives a crimson flame test.
Where it is found
The famous blue geodes come from Sakoany in Madagascar; other important occurrences include Ohio and Michigan in the United States (large crystals around Lake Erie), Sicily and the United Kingdom.
For collectors
Saturated sky-blue colour, gemmy transparency and sharp, undamaged crystals — especially crystal-lined geode halves — are the most sought-after.
