Stone seems more available from the big quarries much earlier than Star Engine turns up.
The Star Engine recipe to simplify gameplay & ease UPS would be plastic, but makes not a lot of flavour sense. The other Star Engine recipes are all pure elements - iron, lithium, uranium, etc. The rich water metals would make sense but we don't need as much gold as copper.
Plastic is (more or less) chains of hydrocarbons, while "stone" is all kinds of metal oxides, silicates, calcium things, etc, different things in different rocks. Stars don't do chemistry. They do nuclear physics. Getting steel & gear wheels out of a Star Engine is already kind of weird (or, Exotic) but getting structured chemistry out would be quite strange theme.
(I personally don't see much manufacturing value in either Star Engine uranium recipe. But they do make a lot of sense both as a flavourful progression through Star Engine mastery, and also as a mod progression research check.)