Earth forming far more diamonds deep inside than thought

Diamonds may not be as rare as previously thought, as there are much simpler processes involved in their formation in deep Earth. A latest study has revealed that diamonds could be formed due to changes in water chemistry indicating their abundance in Earth's mantle.

The findings by the Department of Earth and Planetary Sciences at Johns Hopkins University have been published in the online edition of the journal Nature Communications. The study explores the potential importance of decrease in pH of water or increase in its acidity as a new mechanism for diamond formation.

As water moves from one rock to another, it becomes more acidic – a circumstance that may favour formation of diamonds, the researchers have claimed.

"The role of pH changes associated with water–silicate rock interactions during diamond formation is unknown. Here we show that diamonds could form due to a drop in pH during water–rock interactions," lead author of the report, Dimitri A Sverjensky, said.

Diamond is known to be formed by a complex process called redox reactions that involves electron transfer between methane and carbon dioxide under ultra-high temperature and pressure.

"Diamond formation occurs particularly in the roots of continents known as mantle keels that extend from about 40 to 250 km depth," Sverjensky explained. "In this subcratonic mantle lithosphere environment, diamonds have formed at temperatures in the range of 900–1,400 °C and pressures of about 4.0–8.0 GPa."

However, Sverjensky and his team used a chemical model, yet to be tested with experiments, which showed that diamonds could be formed in host rocks by a simple natural reaction with fluid.

"Diamond can form by pH decreases during water–rock interaction under constant redox conditions in subcratonic lithospheric mantle environments," he said.

"The theory implies that diamonds and their solid and fluid inclusions could be the natural and perhaps even the common result of changes in water chemistry rather than redox changes alone," Sverjensky reiterated.