The way light reflects on the outside of a gemstone is described as its lustre. This lustre will be affected if the stone has been polished, of course. Generally, there are nine descriptors of lustre – metallic, waxy, pearly, silky, vitreous, adamantine, resinous, greasy and dull. I won’t go through all of them but let’s look at some of the most important lustres.

The first is Adamantine: The word refers to diamonds, something that is hard, and reflecting brilliant light. It is derived from the Greek word ‘adamas’ meaning ‘unbreakable’.

Antique diamond bar brooch

Next is Vitreous: ‘Vitrum’ is the Latin for glass, so a gemstone with a vitreous lustre shines like glass. This is the most common lustre and includes emeralds, spinel, topaz, beryls, quartz and tourmalines.

Five stone tourmaline ring

Metallic lustre is where the gemstone shines like a metal. Pyrite, mascasite and haematite have metallic lustres.

1920s to 1930s haematite intaglioring

A Waxy lustre is seen in gemstones such as turquoise, jade, chalcedony and opals.

Edwardian turquoise and seed pearl negligee necklace

And finally, a Resinous lustre, which is when the gem reflects light like resin, hardened tree sap. Amber is the classic example of a resinous lustre.

Vintage amber necklace with ornate gold clasp