Minerals have no condition scale, and the things collectors actually assess are different in kind from a grade.
The four facts
Species, named as precisely as you honestly can — and if you are passing on what you were told, say so and name the source. Locality, which often matters more to a collector than size. Treatment — dyed, heated, irradiated, stabilised, coated, reconstituted. All normal, all declarable. Damage — chips, bruises, cleaved faces, scratches, missing terminations, located rather than described in general.
Natural, treated, repaired
The three words closest to a grade in this trade:
Natural — as it came out of the ground, cleaned at most. Use it only where you can support it. Treated — any of the processes above. Repaired — reglued, a reattached point, a filled crack. Common in larger specimens and always declared.
Contact points are not damage
Where a specimen grew against something else there is a contact face. That is how it formed, not a chip — and a buyer cannot always tell from a photograph, so say which is which. Describing minerals.
What to state alongside
Weight and dimensions, measured. Matrix — on matrix, removed, or a cut base. Sensitivities — soft, water-sensitive, light-sensitive.
There is no grading service
Which means the label does all the work, and an unlabelled specimen loses most of its value to a collector the day the owner forgets what it is.
Questions people ask
Is a cracked specimen worth less?
Yes, and it sells — described.
Does polishing count as treatment?
It is a process worth declaring, especially where it changes how a specimen reads.
Can I grade clarity like a gemstone?
Cut gemstones have their own vocabulary. A mineral specimen is a different thing and is described rather than graded.
More: buying minerals, storing them.