Is Diamond a Mineral or a Rock? (+ 3 Facts You Should Know)

Yes, diamond is considered a mineral. ¹ It meets the criteria to be classified as a mineral as it is a naturally occurring, inorganic solid with a specific chemical composition (carbon) and a definite crystal structure. Diamonds are formed deep within the Earth’s mantle and are mined for various purposes, including jewelry and industrial applications. ²

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Why is diamond a mineral?

Diamond is considered a mineral due to its chemical composition and crystal structure. In general, minerals are naturally occurring, inorganic substances that possess a specific chemical composition and have a characteristic crystal structure. ^{3 4} Diamond meets these criteria and is therefore classified as a mineral.

Chemically, diamond is composed entirely of carbon atoms, which arrange themselves in a specific crystal lattice structure. Each carbon atom in a diamond is covalently bonded to four other carbon atoms, forming a tetrahedral structure. This unique arrangement gives diamond its exceptional hardness and other properties. ⁵

Furthermore, diamonds are naturally occurring. While they are often associated with engagement rings and jewelry, diamonds are actually formed deep within the Earth’s mantle under high pressure and temperature conditions. They are brought to the Earth’s surface through volcanic eruptions. ⁶

Based on these characteristics—chemical composition, crystal structure, and natural occurrence—diamond qualifies as a mineral.

How is diamond different from other minerals?

Diamond is different from other minerals in several ways:

• Hardness: Diamond is the hardest known natural material. It ranks as 10 on the Mohs scale of mineral hardness, which is the highest possible rating. ⁷ This exceptional hardness is due to the strong covalent bonds between carbon atoms in its crystal structure. Most other minerals are considerably softer than diamond.
• Crystal Structure: Diamond has a unique crystal structure. Its carbon atoms are arranged in a tetrahedral lattice, where each carbon atom is bonded to four neighboring carbon atoms. This arrangement results in a rigid, three-dimensional network of atoms. In contrast, many other minerals have different crystal structures, such as cubic, hexagonal, or orthorhombic.
• Composition: Diamond is composed solely of carbon, making it a pure element mineral. Other minerals, on the other hand, can be composed of various elements or compounds, including silicates, oxides, sulfides, carbonates, and more.
• Thermal Conductivity: Diamond has excellent thermal conductivity, which means it can rapidly conduct heat. ⁸ This property sets diamond apart from most other minerals, as they are typically poor conductors of heat.
• Industrial Applications: Diamond has unique properties that make it highly valuable for industrial applications. Its extreme hardness and thermal conductivity make it ideal for cutting, grinding, and polishing hard materials. Diamond is extensively used in industries such as mining, construction, precision machining, and electronics. Other minerals may have different industrial uses but may not possess the same level of hardness or thermal conductivity as diamond.

These distinguishing features make diamond stand out among other minerals and contribute to its high value and wide range of applications.

How are diamonds formed?

Diamonds are formed deep within the Earth’s mantle, typically at depths of 150 to 200 kilometers below the surface. The formation of diamonds involves high pressure and temperature conditions over an extended period. ⁹

There are two main processes through which diamonds are formed: the subduction of carbon-rich materials and the formation in the mantle. ¹⁰

• Subduction of Carbon-Rich Materials: One way diamonds are formed is through the subduction of carbon-rich materials, such as organic sediments or carbonates, into the Earth’s mantle. ¹¹
  
  During the process of plate tectonics, these carbon-rich materials get carried down into the mantle as one tectonic plate is forced beneath another in a process called subduction.
  
  The high pressure and temperature conditions in the mantle then cause the carbon to undergo a transformation, forming diamonds.

• Formation in the Mantle: Another process involved in diamond formation occurs within the mantle itself. The mantle is composed mostly of solid rock, but small pockets of magma exist within it.
  
  These pockets of magma, known as kimberlite or lamproite pipes, act as conduits for diamonds to reach the Earth’s surface. ¹² Within these pipes, diamonds can crystallize from carbon-rich fluids or melts that have originated from deeper in the mantle.
  
  The ascent of magma through these pipes is typically rapid, which helps preserve the diamonds and prevent them from transforming back into graphite, their stable form at the Earth’s surface.

The formation of diamonds requires specific conditions of high pressure and temperature, often referred to as the “diamond stability zone.” It typically takes millions to billions of years for diamonds to form under these conditions. 

After their formation, diamonds can be brought closer to the Earth’s surface through volcanic eruptions. The kimberlite or lamproite pipes mentioned earlier are the primary sources of diamonds mined today.

It is important to note that not all carbon subjected to high pressure and temperature will form diamonds. The right combination of geological processes, along with specific chemical compositions and conditions, is necessary for diamond formation.

Further reading

Is Graphite a Mineral?
Why is Iron a Conductor?
What is the Most Reactive Element?
What is the Most Reactive Metal in the Periodic Table?
Why are alkali metals so reactive?

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