Sedimentary or igneous rocks which have undergone such intense changes in temperature, pressure, structural stress, or chemical environment that they are transformed into denser rocks.
This 1:100,000-scale digital geologic map details the complex early Proterozoic granitic rocks, early Proterozoic supracrustal metamorphic rocks, and Archean crystalline basement of the Black Hills.
Geochemical analysis of rock samples collected and analyzed by the USGS. This dataset includes and supersedes rock data formerly released as "Geochemistry of igneous rocks in the US extracted from the PLUTO database"
This map portrays the geology of Early Proterozoic rocks deposited along the southern margin of the Archean Superior craton during the Penokean orogenic cycle in northern Michigan and Wisconsin.