What rock would never form an aquifer?

Igneous rocks, particularly those that are dense and have low permeability, such as granite, typically do not form aquifers. Their tight crystalline structure inhibits the movement of water, making it difficult for groundwater to be stored or transmitted. Additionally, metamorphic rocks, like schist or gneiss, can also be poor aquifers if they lack sufficient fractures or porosity. Aquifers are more commonly associated with sedimentary rocks, which have higher porosity and permeability.