New York, Nov 4 (IANS): Diamonds may not be as rare as once thought as researchers believe that the precious stone may be more common deep in the earth.

"Diamond formation in the deep earth, the very deep earth, may be a more common process than we thought," said study co-author Dimitri Sverjensky from Johns Hopkins University.

However, the findings may not lead to a deep discounts at your local jewellery stores, as it may be impossible to explore these precious stones physically, the researchers said.

Moreover, the prevalence of diamonds near the Earth's surface -- where they can be mined -- still depends on relatively rare volcanic magma eruptions that raise them from the depths where they form.

The findings are based on a “new quantitative theory of diamond formation”.

Using a chemical model, the researchers found that these precious stones could be born in a natural chemical reaction that is simpler than the two main processes that up to now have been understood to produce diamonds.

Specifically, their model -- yet to be tested with actual materials -- shows that diamonds can form with an increase in acidity during interaction between water and rock.

The common understanding up to now has been that diamonds are formed in the movement of fluid by the oxidation of methane or the chemical reduction of carbon dioxide.

The new research showed that water could produce diamonds as its pH falls naturally - that is, as it becomes more acidic -- while moving from one type of rock to another, Sverjensky said.

The researchers pointed out that it is impossible to physically explore the great depths at which diamonds are created: roughly 144 to 193 km below the Earth's surface at intense pressure and at temperatures about 900 to 1,100 degrees Celsius.

The deepest drilling exploration ever made was about 13 or 14 km below the surface, Sverjensky pointed out.

The study appeared online in the journal Nature Communications.