Gemmology

Gemmology is measurement rather than admiration: every property on this page is something a stone does that a piece of glass does differently. The seventh entry is el plano de exfoliación, the plane along which a crystal splits cleanly because its atoms are held together less tightly in that direction — the property that makes a diamond both the hardest thing a jeweller handles and one of the easiest to ruin with a careless knock. English calls it « cleavage » and keeps that word for minerals; Spanish uses la exfoliación, which is the same word a chemist's shelf uses for scrubbing dead skin off a face, and the same one a botanist uses for bark coming away in sheets. The image underneath all three is one thing: layers lifting off in leaves.