Lamproite, Diamond-Bearing: Lamproite is a less value diamond ore than Kimberlite. Like the more valuable Kimberlite, Lamproite is also found only in the remains of anchient volcanos. Lamproite is an igneous rock believed to have been formed at least 100 miles below the surface. Lamproite deposits have been found on every continent except Europe and Antactica, but are currently only being commercially exploited on a large scale in Australia. The diamonds from a lamproite deposit tend to be darker and smaller than gems recovered from Kimberlite deposits.