You're right and I did miss the part about the plants. However, plants are not the only organisms that derive nutrients straight from minerals. Certain bacteria have also been known to gobble minerals straight.
"Certain bacteria have also been known to gobble minerals straight. " Yes, that's why I mentioned chemosynthesis. It is not very common, and the process is not very well understood yet, but it is even more complicated than photosynthesis and that is why as a source of nutrition for the first life form it is just as unlikely as photosynthesis.