Finding diamonds in the rough

A sorting plant is using optics to separate diamonds from the bedrock they were mined from, and can even detect the particularly valuable pure white and green gems.

A diamond’s sparkle is down to its strong light refraction which disperses visible light. This attribute is being put to used by researchers at the Fraunhofer Institute for Information and Data Processing (IITB). A new optical sorting method identifies the gems among the extracted kimberlite bedrock and separates them out at lightning speed.

At the core of the diamond sorting plant is a high-resolution linescan camera, which, unlike a conventional camera, produces a continuous image rather than sequences of images. The camera faces the fragments of broken rock, which are thrown from a conveyor belt into an intercepting pit. The stones are illuminated from a certain angle as they fall.

If the beams encounter a diamond, the light is deflected towards the camera. This registers the flashes of light and transmits a signal showing their exact position to a computer. The computer is connected to 200 air jets with valves that can be separately opened and closed.