"скала" can be a part of the mountain. Usually people use it to describe the place on the mountain. For example : Он упал со скалы. - He fallen from the rock. "камень" is more like material and also small rocks that u can find on the beach. "горная порода" usually describing what the mountain has, which material is that mountain made from, or even what kind of soil it has. This word usually use in industry. For example some factories need to know something about the mountain before they start to work on it. Sorry, if u still didn't get it 😂 I've tried my best.

Скала - огромный крутой каменный выступ. Камень - кусок твердой породы. Горная порода - то из чего состоят горы, гранит, базальт и т.д.

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