Which type of rock would chemically weather more rapidly marble or gneiss and why

The answer Varies

Explanation:

If you look at the Mohs hardness scale that could also help you & the rocks composition.

marble is less porous and slightly stronger than limestone, but still less durable than granite. (Google)

Take comfort in knowing that gneiss can withstand heavy use; it is made up of minerals in the 6-7 range on Mohs scale, meaning it's harder than glass and about the same hardness as steel.(Google)

Hardness: Being composed of calcite, marble has a hardness of three on the Mohs hardness scale. As a result, marble is easy to carve, and that makes it useful for producing sculptures and ornamental objects. The translucence of marble makes it especially attractive for many types of sculptures. (Google)