How do geologists determine how rocks were formed?

Geologists use observational data to interpret how rocks were formed. When field geologists visit a location, they record data such as the type of rock, structure, and mineralogy. Geologists record their observations in detail to ensure that they remain separate from their interpretations. Once geologists have all the data, they can start to interpret the rocks. This interpretation will ideally describe how the rocks formed. For example, they might observe that a sandstone rock unit has been deposited in an ancient beach environment. When geologists interpret their observations, they use their knowledge of structural geology, sedimentology, and stratigraphy to come to a conclusion. Ultimately, through this process the geologists can begin to understand how rocks were formed.