Coal is which type of rock?

The correct answer is: Sedimentary

• Different ranks of coal are transformed through biological and burial-thermal processes. Additionally, burial-thermal processes also change numerous sedimentary rocks (increasing cementation, etc.)
• Most geologists do not view coal as a metamorphic rock (with the possible exception of meta-anthracite, which is transitional with metamorphic rocks).
• There is confusion since high-rank coals are thought to be the result of "low-grade burial metamorphism" processes.
• Low-grade burial metamorphism continues to occur at temperatures and pressures below those required to produce normal metamorphic rocks (marble, quartzite, slate, etc.). Hence, it is a sedimentary rock.