Transformed rocks main content.

Transformed rocks

Part of Hall of Planet Earth.

Transformed Rocks AMNH/R.Mickens

Working in the Scottish Highlands, the geologist G. M. Barrow discovered in 1893 that an extensive layer of rock, once a uniform sediment, shows progressive transformation of its mineral content. He realized that the specific minerals depend on the extent to which the rocks had been heated. The metamorphism transformed the rock into different kinds of schists. This systematic evolution of mineral content is known as Barrovian zoning, and is seen in eroded mountain ranges worldwide.

Barrovian Zoning_ILL

In This Section

Exhibit Barrovian sequence These four samples were originally identical shales whose mineralogy changed as they were subjected to increasing pressure and temperature. Exhibit Ultra-high pressure rock The presence of diamond in this rock indicates that it had been buried to a depth of about 130 kilometers. Exhibit Gore Mountain garnet This sample of garnet-bearing amphibolite is a spectacular illustration of how metamorphism and deformation can cause a complete...