Kunzite

Kunzite is spodumene coloured pink to lilac by manganese. Spodumene is otherwise an industrial mineral — it is the principal hard-rock lithium ore — which makes this one of the few cases where a major battery raw material also has a gem variety.

It is awkward in three ways at once. It has perfect cleavage in two directions, so it splits readily and is difficult to cut and to set. It is strongly pleochroic, showing near-colourless, pink and violet down different axes, so the orientation of the cut decides the colour of the finished stone. And its colour is unstable: prolonged exposure to daylight fades it, which is why it is sometimes called an evening stone and why museum specimens are kept out of the light.

A great deal of commercial material is irradiated to deepen the colour, and irradiated stones fade faster than natural ones.

Pink, transparent, with two perfect cleavages meeting at close to eighty-seven degrees and strong pleochroism. Denser than the beryls and softer, which separates it from morganite — the confusion it is most often part of.

Gemstone, in large faceted stones where the material allows it, and it does: pegmatite crystals are large and clean, and cut kunzites of hundreds of carats exist.

Not a stone for daily wear, on cleavage and on light sensitivity together.

Named in 1902 for George Kunz, gemmologist to Tiffany, who first described it. He named morganite nine years later, so two of the gemstones named in that decade are down to one man.