Gems & Gemology, Fall 1990, Vol. 26, No. 3
Recent Discoveries of Large Diamonds in Trinity County, California
Rudolph W Kopf, Cornelius S. Hurlbut, and John I. Koivula
Although California has produced over 600 diamonds, some of which have been of gem quality, the largest until recently weighed approximately 6 ct. In the early 1980s, however, Edgar J. Clark found a 3.90 ct stone; in 1987, he discovered three stones weighing 32.99, 17.83, and 14.33 ct. These four diamonds were recovered from stream gravels of Hayfork Creek in Trinity County, California. All four are of industrial grade and all have one interesting feature in common, that is, two generations of diamond growth. The initial crystal, or group of crystals, is encrusted by a later generation of diamond overgrowth that, although it conforms crystallographically to the underlying crystal, shows different crystal forms. This unusual feature, common to all four crystals, would indicate that they originated from the same source.