Full Idea
Aristotle conceives of the necessary features of objects, traditionally known as the 'propria' or 'necessary accidents', as being distinct and derivate from, the essential features of objects.
Gist of Idea
The 'propriae' or 'necessary accidents' of a thing are separate, and derived from the essence
Source
report of Aristotle (Metaphysics [c.324 BCE], props) by Kathrin Koslicki - Essence, Necessity and Explanation 13.1
Book Reference
'Contemporary Aristotelian Metaphysics', ed/tr. Tahko,Tuomas [CUP 2012], p.187
A Reaction
This is a vague area, because Aristotle says very little about it. See Ideas 12266 and 12262. A particular shape of mole might be yours alone, but not part of your essence. That may be an 'idion' rather than a 'propria' (or are they the same?).
Related Ideas
Idea 12266 'Same' is mainly for names or definitions, but also for propria, and for accidents [Aristotle]
Idea 12262 An 'idion' belongs uniquely to a thing, but is not part of its essence [Aristotle]