Celestine geode – Madagascar

Celestine – a sky-blue mineral

Celestine is a mineral composed of strontium sulfate with the chemical formula SrSO₄. It belongs to the sulfate mineral group and crystallizes in the orthorhombic crystal system. Its name refers to the delicate sky-blue colour displayed by some of the most sought-after specimens. However, celestine is not always blue. It may also occur as colourless, white, grey, yellowish, pinkish or pale green. The crystals are usually transparent to translucent and have a vitreous lustre, sometimes appearing pearly on cleavage surfaces.

Crystals and appearance of celestine

Celestine forms tabular, prismatic and elongated crystals. It may also occur as crystal clusters, geodes, fibrous aggregates or compact and granular masses. Although it may appear delicate and light, it is relatively heavy due to its strontium content.

How does celestine form?

Celestine most commonly forms in sedimentary rocks and in deposits created by the evaporation of mineral-rich waters. It is often associated with gypsum, anhydrite, halite, calcite and other minerals. Crystals may grow in cavities and geodes, where they have enough space to develop well-defined crystal faces. Their colour, size and shape are influenced by the conditions of formation and the mineral impurities present.

How to care for celestine

Celestine is relatively soft, brittle and has pronounced cleavage. Specimens should therefore be handled carefully and protected from falls, impacts and scratching by harder minerals. Dust is best removed with a soft, dry brush. Crystal clusters should be stored separately or displayed in a sufficiently spacious cabinet to prevent damage to delicate edges and crystals.