What factor primarily influences the porosity of a rock formation?

The primary factor influencing the porosity of a rock formation is its mineral composition. Porosity refers to the volume of void spaces in a material, and this characteristic depends significantly on the types of minerals present within the rock. Different minerals have distinct abilities to form and retain void spaces; for example, sedimentary rocks, such as sandstone, often have higher porosity due to their granular nature and the presence of pores between the grains. Conversely, igneous rocks, which often form through solidification of molten material, typically have lower porosity due to their dense crystalline structure.

The age of the rock, temperature of surrounding waters, and altitude are secondary factors that may indirectly affect porosity but do not serve as the primary influences. For instance, while certain geological processes over time can alter porosity, it is fundamentally the mineral characteristics that most directly determine the potential for void space within the rock.