According to an online Oxford dictionary
Rock: the solid mineral material forming part of the surface of the earth and other similar planets, exposed on the surface or underlying the soil.
But it doesn’t tell you what it’s made of exactly.
Strangely theyare mostly made of oxygen!
The answer is they can be made from a very wide range of materials (all of which can be found in the periodic table!).
Metals (and silicon) are quite reactive and oxygen is very reactive so when you combine the two they made a very stable compound (metal or silicon oxide). For example, kaolinite (China clay) is a common clay made of sheets of silion and aluminium oxide.
But you also get rocks like limestone which are made from calcium carbonate (CaCO3 = still alot of oxygen in it).
Hopefully this answers your question, if you’ve got anymore please let me know!
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