Experts Probe Mystery of the "Impossible Diamonds"

(IDEX Online) - Researchers have identified a pair of "impossible" diamonds - found side by side, yet with inclusions that suggest they originated from completely different chemical environments.

They were found at De Beers' now-closed Voorspoed mine, in South Africa, and examined by a team led by experts at Hebrew University's Institute of Earth Sciences and Nanocenter, in Israel.

What makes these diamonds special is that the inclusions - minuscule traces from the rock surrounding them on their volcanic journey from deep in the Earth's mantle - were previously thought to be completely incompatible.

One stone has inclusions of nickel-rich carbonate minerals, which are rich in oxygen and represent an oxidized chemical environment.

The other has inclusions of oxygen-poor nickel-iron alloys, representing a reduced (oxygen-poor) chemical environment.

This combination of oxidized carbonate inclusions in one diamond and reduced nickel alloy inclusions in the other is highly unusual because these substances normally do not coexist—they react quickly and neutralize each other.

Researchers Yael Kempe and Yaakov Weiss suggest a process called "redox freezing" is responsible.

The expected reaction between two "opposing" diamonds - one rich in oxygen, the other poor - is halted by a sudden temperature or other environmental change. It prevents them from either merging into a single stone, or destroying each other.

The team's findings, published in the journal Nature Geoscience, provide new insight into deep Earth chemical processes involved in diamond formation and mantle chemistry.

Pics courtesy Yael Kempe and Yaakov Weiss.