Unmetamorphosed

Unmetamorphosed refers to geological materials, most commonly rocks, that have not undergone metamorphism. Metamorphism is a process in which existing rocks are transformed by heat, pressure, or chemical reactions without melting. Therefore, unmetamorphosed rocks retain the original mineralogy and texture they possessed when they were formed.

In the context of sedimentary rocks, unmetamorphosed means they have not been subjected to the conditions that would cause recrystallization, mineral changes, or the development of foliation. For example, a sandstone that has not been metamorphosed might still show the original clastic texture with visible sand grains cemented together. If it were metamorphosed, it could become quartzite, a rock with a significantly altered texture and interlocking quartz crystals.

Similarly, igneous rocks are considered unmetamorphosed if they have not been altered by subsequent geological processes. While igneous rocks form from molten magma or lava and have their own distinct textures, they can still be affected by low-grade metamorphism. An unmetamorphosed igneous rock is one that has escaped these changes, preserving its original igneous characteristics. The term is crucial for distinguishing between rocks that have retained their original formation characteristics and those that have been significantly altered by geological forces.