Peanut butter contains levels of carbon

Edinburgh University experts say the feat is made possible by squeezing the paste between the tips of two diamonds creating a "stiletto heel effect".

The scientists also revealed they can turn oxygen into red crystals using the same method.

Demonstrations take place at Royal Society exhibition shows from 2 July.

Many carbon containing materials can be converted into diamonds - including peanut butter

Prof Malcolm McMahon

Edinburgh University

Professor Malcolm McMahon, based at the Centre for Science and Extreme Conditions at Edinburgh University, is one of the scientists involved.

He said: "Pressure can cause extraordinary changes in all kinds of materials and can create completely novel materials.

"We are currently developing techniques that will create pressures of up to five million atmospheres, much higher than the pressure at the centre of the earth, to find the holy grail of high-pressure physics, the metallic phase of hydrogen.

"If we manage to make metallic hydrogen, the next step will be to make enough to study it in real detail, which would mean using much larger diamond anvils, about the size of your thumb, to squeeze it."

He added: "Obviously large gem-quality diamonds would be extremely expensive, so we are looking at ways to make them artificially.

"Many carbon containing materials can be converted into diamond including peanut butter."

Dr Colin Pulham, who is also based at the Edinburgh University, said: "Submitting substances to extremely high pressure is a valuable means for understanding their stability.

"High pressure testing of pharmaceuticals is becoming a useful technique to screen new and existing drugs.

"Understanding what happens to a drug's structure and its properties under pressure could lead to the development of medication which is better suited to hotter climates, or to the development of new forms of medication."

The free exhibition runs from Monday 2 to 5 July 2007.