Many people assume a diamond’s renowned hardness would make it impervious to molten rock. Understanding what truly happens when a diamond encounters lava requires examining the distinct properties of both. The interaction is not about melting, but a different chemical process.
What a Diamond Is
A diamond is a unique form of carbon, composed entirely of carbon atoms arranged in a highly stable, repeating crystal structure. This atomic arrangement gives the diamond its exceptional properties. It is recognized as the hardest naturally occurring substance on Earth, ranking a perfect 10 on the Mohs hardness scale. Its intricate internal structure contributes to its remarkable density and resistance to scratching.
What Lava Is
Lava is molten rock that has erupted from a volcano and flowed onto the Earth’s surface. Its temperature typically ranges from about 700°C to 1,200°C (1,292°F to 2,192°F). As lava flows, it is exposed to the Earth’s atmosphere, which contains oxygen. This exposure is a significant factor in how materials react to the extreme heat of molten rock.
Diamond’s Reaction to Lava
Diamonds do not melt when exposed to lava because their melting point is far higher than surface lava temperatures. A diamond’s melting point is approximately 4,027°C (7,280°F). Instead of melting, a diamond undergoes a process called combustion or oxidation when subjected to the heat of lava in the presence of oxygen. The carbon atoms react chemically with oxygen in the surrounding air.
At temperatures reached by lava, generally around 850°C to 900°C (1,562°F–1,652°F), the carbon in the diamond combines with oxygen. This chemical reaction converts the solid carbon into a gaseous form, primarily carbon dioxide. The presence of atmospheric oxygen is the key element facilitating this transformation. Rather than melting, a diamond exposed to lava and air will gradually turn into an invisible gas.
Diamond’s Limits and Resilience
While diamonds are celebrated for their exceptional hardness and resistance to many forms of chemical degradation, their durability has specific boundaries. They are highly resistant to scratching and abrasion, a property that makes them valuable in both jewelry and industrial applications. However, this strength does not extend to high temperatures when oxygen is available. The chemical composition of diamond, being pure carbon, makes it susceptible to combustion under these conditions.
Diamonds form deep within the Earth, typically around 100 miles below the surface, under conditions of extreme heat and pressure, and crucially, in an environment devoid of oxygen. These formation conditions are fundamentally different from the oxygen-rich, lower-pressure environment of a surface lava flow. The diamond’s ability to exist in nature, despite its combustibility, is a testament to the oxygen-free conditions of its deep Earth origins, contrasting sharply with its vulnerability when exposed to the atmosphere and intense heat.