These rocks occur in massive formations and beds extending over several hundred kilometers in many cases. 5. Limestones: These are the most common sedimentary rocks from the nonclasticgroup and are composed chiefly of carbonate of calcium with subordinate proportions of carbonate of magnesium. They are formed both biochemically and mechanically.
Burial metamorphism commonly occurs in sedimentary basins, where rocks are buried deeply by overlying sediments. As an extension of diagenesis, a process that occurs during lithifiion, burial metamorphism can cause clay minerals, such as smectite, in .