We all know that the oxygen levels increase and decrease as well as the temperature, so I believe it's safe to assume atmospheric pressure changes as well... And since granite and basalt are formed with heat and pressure and stuff cooling.. is there any feasible scenario that could make granite behave like clay, if the atmospheric pressure was different as well as the ambient temperature? Could drastically different conditions make granite cool so slowly it could be molded?


1 Answer 1


Does granite and basalt behave differently in different atmospheric pressures?


Yes, but not directly. Granites form in the deep Earth, so they don't really care about small differences in oxygen or atmospheric pressure above them. They are going to remain identical whether the pressure on them is 1000 atmospheres, or 1001 atmospheres.

However, granites crystallise from molten magma. To make molten magma, you need to take something that's initially solid, and then heat it up. Often, these things that are molten to form the magma that ends up as granite used to be at the surface of the Earth, and then got buried at depth for whatever reasons (usually movement of tectonic plates).

These "things" are sedimentary rocks. And if those sedimentary rocks formed when the atmosphere had lots of oxygen (such as the past 600 million years or so), then the magma will be oxidised. If they are earlier, they might be reduced (the opposite of oxidised).

Whether a magma is oxidised or not will affect how the granite looks like. Oxidised granites are often a pink because the iron they contain is "rusty". Non-oxidised granites will be whiter or grey. This tells us a bit about Earth history and past atmospheric conditions.


Everything I said for granites is also relevant for basalts (and their deep equivalent, called "gabbro"). For example, oxidised basalts might have a mineral called "magnetite" which is magnetic. But this is at depth. As for basalt lava flows on the surface, the effect of the atmosphere is negligible and don't expect much to happen.


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