Platinum nugget, Kondyor Massif, Khabarovsk Krai, Far Eastern Federal District, Russian Federation. Photo Heritage Auctions

In the remote wilderness of Far Eastern Russia, inland from the Sea of Okhotsk, is a circular feature some six kilometers across that looks exactly like a meteorite impact crater: It isn't. Although the towering walls of the structure, some 2000 feet high, look very much like the crater rim of a volcano: They're not.

The structure, called the Kondyor Massif, represents the remains of an Dunite intrusion: a mass of magma with origins deep in the mantle, that carried valuable amounts of the rare metals: Platinum, Rhodium, Gold and others to the surface of the planet. Weathering allowed the rare metals to migrate downstream, forming placer deposits. Analysis of Zircon grains in the Dunite shows that the Platinum Group Elements (PGE's) formed deep in the mantle some 2.4-1.8 billion years ago. Much later, they were injected into the surface crust some 176 -143 million years ago.

Being rich in PGE's, the massif was responsible for approximately 4 tons of Platinum being produced in one year. Compared to the production of most Gold mines, this is nothing. Nuggets of Platinum the size of this one, are as rare as the proverbial hen's teeth.

Deceptively heavy for its size this rounded, silvery nugget weighs 7.368 ounces troy or 229.2 grams - over half a pound! It measures a 1.63 x 1 inch (4.22 x 2.55 cm). [Scale: 1 inch, with mark at 1 cm]. Estimated Price: $40,000 - $50,000

Heritage Auctions. 2013 June 2 Natural History Signature Auction Session 2. Phone: 800.872.6467 - Email: Bid@HA.com