How are nonfoliated metamorphic rocks formed?
Nonfoliated rocks are produced mainly by contact metamorphism, or heat from cooling magma. Contact heat generally results in a finer recrystallization of the parent rock, so little foliation is visible. Quartzite is typically a tough, hard, light-colored rock in which all the sand grains of a sandstone or siltstone have recrystallized into a fabric of interlocking quartz grains. Marble is a softer, more brittle rock in which the dolomite or calcite of the limestone parent rock has recrystallized. Hornfels is a common metamorphic rock formed when basalt or shale is exposed to heat from magma.
