Metamorphic rock Metamorphic rock Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure ( or more), causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath
Fire-cracked rock Fire-cracked rock In archaeology, fire-cracked rock (FCR) or fire-affected rock (FAR), is rock of any type that has been altered and split as the result of deliberate heating. It is a feature of many archaeological sites, throughout the United States. In many cases, fire-cracked rock results when stones were used to line hearths and earth ovens or were heated to provide a longer-lasting heat-source (similar to a modern hot water bottle). In other cases, fire-cracked rock results from stone being used to heat or boil water; the stones were heated and dropped directly into water held in containers made of