“Diamonds are formed from compressed coal.”

The most convincing evidence that coal did not play a role in the formation of most diamonds is a comparison between the age of Earth's diamonds and the age of the earliest land plants. Almost every diamond that has been dated formed during the Precambrian Eon... much older than almost every diamond that has ever been dated.

Diamonds are a solid form of carbon with a distinctive cubic crystal structure. They are generally formed at depths of 100 to 150 miles in the Earth's mantle.

While Hollywood's depiction of Superman squeezing coal captured the public's imagination, in reality this does not work. Coal is a crustal compound and is not found at mantle pressures. Also, we now know that diamond does not prefer to form through direct conversion of solid carbon, even though the pressure and temperature conditions under which diamond forms have traditionally been studied experimentally as the reaction of graphite to diamond.

Let's put this classic misconception to rest: natural diamonds are not made from coal. While it makes for a poetic idea, transforming something ordinary into something extraordinary, it simply isn't scientifically accurate. Coal forms from decayed plant material found much closer to the Earth's surface. Natural diamonds, on the other hand, originate from pure carbon deep in the Earth's mantle, far below where coal ever forms.

Diamonds are formed deep within the Earth's mantle under extreme conditions, at depths ranging from 150 to 200 kilometers, where temperatures soar between 1,000 to 1,300 degrees Celsius. The carbon that forms diamonds typically originates from two main sources: Subducted Oceanic Crust and Primordial Carbon.

Diamonds form deep in the mantle, typically 150 to 200 km below Earth's surface. Some rare diamonds originate as deep as 800 km, far below the crust. Many natural diamonds are over 1 billion years old, with some dating back 3.5 billion years. They grow from carbon-rich fluids moving through cracks in mantle rocks.

The primary element necessary for diamond formation is carbon. This carbon begins in a simple form such as graphite, and under specific conditions, it transitions into a crystalline structure known as a diamond. Graphite is a stable form of carbon at the Earth's surface, but deep in the Earth, conditions are ripe for transforming carbon into diamonds.

The process of making diamonds begins by cutting very small pieces of a real diamond to produce tiny scraps that are call waivers. These waivers are then placed ... (focuses on synthetic, but implies natural from mantle carbon).

Diamond isn't made of organic C at all. Organic matter would rather become oil, gas, coal or dissolve entirely. C itself isn't very common in earth's mantle, but subducted eclogites and peridotites can lead to the needed C-accumulation.

Diamonds were formed over 3 billion years ago deep within the Earth's crust under conditions of intense heat and pressure that cause carbon atoms to crystallize.

Another fascinating theory suggests some diamonds may indeed originate from organic materials like ancient biomass or even coal carried deep into the mantle by tectonic plates. As these sediments descend under immense heat and pressure, they can recrystallize into diamond structures—but this process accounts for only a small fraction of all natural diamonds found today.

A terribly common misconception that's persisted for decades is that diamonds are made from the metamorphism of coal. However, this theory is highly unlikely because most diamonds are so prehistoric, they actually date back millions of year. Therefore, most naturally-occurring diamonds are older than all plant life on Earth, which is the source material of coal. However, there is a slight possibility that coal may have played a part in some of the diamond formation processes.

The vast majority of natural diamonds are formed from carbon that existed in the Earth's mantle long before the first land plants, which are the source of coal, evolved. This fundamental age difference is a primary reason why coal is not the source material for most diamonds.

Scientific consensus from sources like the USGS and peer-reviewed literature confirms that natural diamonds form primarily from inorganic carbon in the Earth's mantle under extreme pressure and temperature, predating coal formation from land plants by billions of years. Rare exceptions like impact or subduction diamonds may involve organic carbon, but coal is not a primary source.