Full Idea
If earth is air-esque and earth is (not fire but) fire-esque, then it is fire that is primary matter. Such matter is not a this-something.
Gist of Idea
Primary matter is what characterises other stuffs, and it has no distinct identity
Source
Aristotle (Metaphysics [c.324 BCE], 1049a25)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.271
A Reaction
For being a 'this-something' read 'having determinate identity'. Aristotle's account of 'primary matter' is controversial and much discussed.