This is a follow up question to my previous question: Rock/Mineral Ore Eating Organism
So these things: https://en.wikipedia.org/wiki/Lithoredo
They eat limestone. So I thought, what is limestone rich in? Calcite/Calcium. Perhaps a similar, more alien species of boneless mollusks could synthesize the minerals from limestone and also phosphorite for phosphate and grow bones, an entire skeleton even and evolve into humanoids.
Is this too far fetched or is this kind of biosynthesis reasonable within the realms of science fiction?
Edit: forgot to factor in collagen, but:
The major elements present in the mollusc tissues were sodium, potassium, magnesium, calcium, iron and zinc. Collagen was found to be the major protein in edible molluscs, and aspartic acid, glutamic acid, glycine, alanine and leucine were found to be the dominant amino acids.
Edit: changed "sandstone" to "limestone", my mistake!