Full Idea
There might be more than one natural kind that shares the same superficial features, …jade, for example, has two forms, jadeite and nephrite, which are similar in superficial properties, but have different chemical composition and structure.
Gist of Idea
Jadeite and nephrite are superficially identical, but have different composition
Source
Alexander Bird (Philosophy of Science [1998], Ch.3)
Book Reference
Bird,Alexander: 'Philosophy of Science' [UCL Press 2000], p.105
A Reaction
It might be questioned whether jadeite and nephrite really are natural kinds, either together or separately.