Royston turquoise district

The best of it is described by the US Geological Survey as equal to any American turquoise.

That verdict sits in the survey's record for the Royal Blue Mine, a past producer of gemstone in Nye County, Nevada, and the main producer of the Royston district. The record grades the colour from dark sky blue through to pale light blue, and notes that the best material is very fine indeed.

Where the colour sits in the rock is the useful part. The best and darkest turquoise is found in limonite-stained rock, while the paler, softer blue comes out of a light-coloured, softer porphyry. Turquoise is the ore and malachite the gangue, and there is breccia stained with malachite a few hundred yards away. The host is a felsic volcanic rock, a trachyte, altered by silicification and argillization, and the turquoise occupies veinlets, seams, lenses and nodules averaging around 13 centimetres thick.

For a while it poured out stone. The survey records that the mine produced 1,250 pounds of turquoise a month, or more, and the workings behind that are substantial: five tunnels, three shafts, three open pits and a scatter of smaller ones, running to about 139 metres of length and 12 metres of overall depth.

The ownership history reads like most Nevada gem mines, which is to say it changed hands constantly. Workman and Davis sold the mine to William Petry for 3,000 dollars, and Petry developed it, got it producing, and sold it in 1907 to the Himalaya Mining Co., owned by Julius Tannenbaum of Los Angeles and New York. It was systematically worked through 1908 and 1909, sold back to Petry in 1911, mined for a while by Petry and W.I. Miller, then leased to Leehand and Bert Kopenhaver, who worked the dumps and then bought the mine outright. It changed hands many times through the 1930s and 40s with intermittent production.

Turquoise is where Nevada mining starts. The Nevada Bureau of Mines and Geology frames the state's whole mining history as running from the era of hand-dug turquoise and salt mines, through the Comstock and its deep underground silver, to the Carlin era of huge bulk-mineable gold. Modern mining in Nevada began in 1849 with placer gold found in a stream running into the Carson River. The turquoise was being dug long before that.

The survey locates this to within a kilometre, so treat the pin as the district rather than a doorway, and check ownership before you set foot on anything.