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When the alchemist creates an extract, he can place two formulae into one extract. When the extract is consumed, both formulae take effect. This extract has a level two levels higher than the highest-level formulae placed in the extract.
I would say that it is One Extract but it is two different Formulae. So its basically a Transmutation Portion and a Conjuration Portion (as per your example).
I have a character with a similar build coming up, so I would also be interested in the answer.
Rez / bump / dot.
Was this ever answered?
It should work fine. It would have the schools and subschools of both extracts. I can't see how you could justify removing a subschool without some kind of rule to that effect.