Coal is an organic sedimentary rock belonging to the biochemical subclass. It is primarily composed of carbon, hydrogen, and oxygen, with various impurities such as sulfur, nitrogen, and trace minerals. Coal forms in various grades, from the softer and less carbon-rich lignite to the harder, more carbon-rich anthracite. Its general appearance varies from dull black to lustrous black, depending on the grade and impurities present.

Mineral Makeup

Coal is mainly composed of carbon, along with varying amounts of hydrogen, sulfur, nitrogen, and trace elements. The specific composition of coal depends on the type and grade of coal, as well as the conditions under which it formed. Some trace minerals found in coal include quartz, clay minerals, calcite, and pyrite.


Coal forms through the accumulation, compaction, and transformation of plant material in swampy, low-oxygen environments over millions of years. As the plant material accumulates and becomes buried, it undergoes a series of chemical and physical changes, gradually transforming into peat, lignite, bituminous coal, and eventually anthracite, depending on the temperature and pressure conditions experienced during its formation.


Coal deposits are found in sedimentary rock formations throughout the world, often in regions that were once swampy or covered by shallow seas. Geographically, significant coal deposits can be found in the United States, Russia, China, India, and Australia, among other countries.


Though not traditionally considered a metaphysical stone, coal has been associated with several symbolic meanings. It is often seen as a symbol of transformation, due to its origin from plant material and its role in fueling the industrial revolution. Coal is also believed to represent endurance and perseverance, as it has withstood millions of years of pressure and heat to become the energy-rich rock it is today.

ClassSedimentary (Organic)
Mineral MakeupPrimarily carbon, hydrogen, oxygen, and various trace elements 
LusterDull to lustrous 
Hardness (Mohs)1-2 (lignite) to 2-3 (anthracite)
StreakBlack to brownish-black
ColorBlack, varying in luster depending on grade and impurities
CleavageNone, exhibits a conchoidal fracture
Specific Gravity1.3 (lignite) to 1.8 (anthracite)