Because it is often difficult to determine the mineral composition of volcanic rock visually, geologists prefer to classify igneous rock by its mineral content whenever possible, with the relative volume percentages of quartz (crystalline silica), among other minerals, being important determinants. For example, what separates basalt from andesite is the former's lower quartz content. Some common uses of basalt include:

• Cobblestones for paths

• Flooring tiles

• Ballast rock for railroad tracks

• Roadstone