Other Semi-Precious Gemstones

Other Semi-Precious Gemstones

This is where the less familiar stones live: rarer gem species and collector minerals that do not have a collection of their own. Each has its own chemistry and character, from iolite (cordierite, Mg2Al4Si5O18), which changes from violet to almost colorless as you turn it, to scapolite that glows under ultraviolet light.

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Gemstone guide

Other Semi-Precious Gemstones

About these gemstones

Many of these stones are well known to gemologists but rarely seen in jewelry shops, either because they are found in only a few places, because clean crystals are scarce, or because they are too soft for everyday rings. Several are sought by collectors for a particular property: strong pleochroism, high dispersion, fluorescence or an unusual color that no common gem matches.

Did you know?

Iolite's mineral, cordierite, came out as a promising candidate for the legendary Viking sunstone in a computer simulation of navigation by polarized light.

How to recognise these stones

Each species has its own signature. Iolite is strongly pleochroic, violet-blue from one side and grey to almost colorless from another. Scapolite and cerussite often fluoresce under UV light, and cerussite, a lead carbonate, is unusually heavy. Tiger's eye shows a moving band of light, called chatoyancy, across its golden brown fibers.

Caring for these stones

Hardness varies widely here, from soft cerussite and orpiment to harder kornerupine and iolite, so check the listing and treat softer pieces gently. Clean gemstones with a soft brush and lukewarm soapy water, and keep mineral specimens dry and dust them only. Cerussite contains lead and orpiment contains arsenic, so handle them as display specimens, wash your hands afterwards and keep them away from children; orpiment should also be kept out of strong light.

Every stone is natural, and each listing gives its weight, size, origin and treatment, with photos of the actual stone.