* Porosity refers to the amount of empty space within a rock. Rocks with higher porosity can hold more water.
* Permeability refers to how easily water can flow through a rock. Rocks with high permeability allow water to pass through them quickly.
Grainy rocks can have high porosity, but they might not have high permeability. For example, sandstone can be very porous due to the gaps between sand grains, but the grains can be tightly packed, making it difficult for water to flow through.
Crystalline rocks can also have high porosity, depending on their structure. For example, some metamorphic rocks like marble have many interconnected fractures, allowing water to pass through them.
Ultimately, it's the specific rock type and its unique properties that determine its ability to absorb water, not simply whether it's grainy or crystalline.
