Mineralogy

A pyrite cube has less symmetry than a cube, and its striations say so. Crystal faces lie along the densest planes of atoms inside.

A UV lamp does not report the mineral. It reports the trace atoms inside it, which is why two pieces of one species behave differently.

Whether a crystal's colour tells you anything depends on one thing: is the colouring element part of the mineral, or a guest in it?

Kyanite was once called disthene, two strengths. It takes a scratch differently along the blade than across it, and both figures get printed.

Druzy names the crystals now. For two hundred years it named the hole they grew in, and mineralogy never fully gave up the older sense.

Amethyst, agate, jasper and carnelian are all quartz. Yet agate from one Moroccan field ran to nearly a third moganite, a separate mineral.

Urea is an approved mineral species. The definition it cleared says normally crystalline, and never says inorganic at all.

The million years attached to the Naica crystals measures one metre across, not eleven metres long. Nothing dated there reaches it.

A geode is a sequence, not an interior. Three more minerals grew inside a Brazilian amethyst geode after the amethyst, and the rind went first.

Crystals grow from melt, from water, from hot fluid, and inside solid rock that never melted. The fourth one is where garnet comes from.

Gem essence is water that has been exposed to a crystal. Here is what is actually in the bottle and which crystals are safe to use.

Crystal clusters form by elimination. Many crystals nucleate on a cavity wall pointing in random directions, and the ones whose fastest growth direction happens to…