Observable language
Colour and phenomena
The interface separates what the stone does from the trade name someone might attach to it.
Colour change and colour shift
Colour change means the dominant hue changes between recorded lighting conditions. Colour shift means movement within a hue. A shift is not promoted to a change.
A colour-change claim needs a paired record with the light source and colour temperature for each image; two unlabelled photographs are not evidence of the conditions.
Chatoyancy and asterism
A cat’s-eye or star is described by what is observable—sharpness, movement, completeness and viewing conditions. The phenomenon does not establish species or origin.
Other phenomena
Adularescence, aventurescence, labradorescence, play-of-colour and tenebrescence use controlled terms. Visible dispersion may be described as an observation, not as a laboratory identity claim.