Catalog numbers, and marking the specimen
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The number is the thread that survives a box being dropped, a label being soaked and a collection being sold twice.
Why a number at all
Because a label and a specimen can separate, and when they do the number on the stone is the only way back to the data.
It also makes the catalog usable: you can sort, search, lend, sell and insure by number in a way you cannot by description.
A scheme that survives
Sequential, simple, never reused, never restarted. 1, 2, 3 works and is used by collections a century old.
A year prefix reads well and tells you when something entered the collection: 2026-0147.
What does not survive is a scheme that encodes meaning, species, locality, drawer. Every one of those changes eventually, and then the number lies.
Leave gaps for nothing. Sequence is the point.
Marking the specimen itself
The museum convention is a small patch of a reversible barrier coat, the number written on it in permanent ink, and a second coat over the top. Reversible matters: it can be removed without touching the specimen.
Put it somewhere unobtrusive but findable: the back, the base, the matrix rather than a crystal face.
Never directly onto a porous, soluble or friable surface, and never onto a crystal face at all.
For micromounts and tiny material the number lives on the mount or the box, because the specimen has nowhere to take it.
What not to do
Ink straight onto the stone with no barrier, which is irreversible and looks it.
Correction fluid, which yellows, embrittles and is exactly what a conservator has to remove.
An adhesive label on the specimen, which falls off and takes a flake with it.
And engraving, which is permanent damage in the name of record-keeping.