Gold has been the key standard of value since prehistoric times, the durable metal most easily extracted from the earth and most readily purified and shaped. Its discovery in concentrations -- lodes -- has set off migrations of prospectors seeking instant fortune.

It was the lure of gold that prompted most of the explorations of the New World, and Captain John Smith forayed from Jamestown certain that he would find evidence of native goldsmithing as the Spanish had in South America. But gold did not turn up in North American until 1829, when two brothers discovered it on their farm in Spotsylvania County, Virginia. For the next dozen years millions of dillars' worth of gold was shipped to the mint in Philadelphia from mines throughout Appalachia, including one worked off and on until the 1950s near Great Falls, Maryland. What essentially ended gold mining in the East was the discovery of richer lodes in California, then Alaska.

The Smithsonian Museum of Natural History has put together an extraordinary new exhibit of gold in crystalline and nugget form, augmenting its own collections with that assembled by banker Charles Crespi of Angel's Camp, California.

"Gold, like most minerals, originates in crystal form," according to John Sampson White, Smithsonian associate curator. "It occurs in lode rock deposits as flattened plates or as branching, lacy or spongy clusters.

"Erosion disintegrates the rock, releasing the crystals into rivers. Collisions with pebbles and boulders in swiftly flowing water hammer the crystals into nuggets.

Included in the exhibit is a five-pound nugget from California and a 57-ounce crystaline piece among four turned up in California in the 1920s.

An adjunct exhibit is of the even rarer metal, platinum, with nuggets from Russia and Colombia, the major producers.

A note on inflation: during the decade after the Spotsylvania gold discovery, gold was priced at about $20 an ounce. In these times, the price changes almost that much in a day, reaching toward $500 an ounce. Yet the quantity of refined gold in the world is more than 2,000 percent greater than in 1829.