There are minerals that contain hydrogen
Again, I'm not a geologist and what I'm saying is probably nonsense. Hornblende is an igneous rock. Hornblende has the following chemical formula:
Ca2(Mg,Fe,Al)5(Si,Al)8O22(OH)2
Note the "OH" on the tail end of the molecule. My uneducated hunch is that hornblende though an igneous rock, forms in an aqueous environment deep underground such as super heated water under high pressure. I'll stop here before I dig myself in deeper and let an expert respond.
Gary
