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paul storr silver
The Leadhills orefield produced the greatest amount of silver. Between 1845 and 1919 twenty three tonnes were recovered from argentiferous galena, the richest lead ore producing 312 g/tonne. Significant amounts of native silver were found at Alva, near Stirling and Hilderston, near Bathgate.
Stephen Moreton presents the history and mineralogy of the silver deposit at Alva in an excellent article in the Mineralogical Record. In addition to describing the geology and mineralogy, he paints a lurid tale of Jacobite rebellion, fortunes made and lost, buried treasure, betrayal, deals with the government and a diversity of charming and not-so-charming characters.
The deposit, epigenetic hydrothermal veins in andesitic lavas, was worked intermittently from 1715 until 1768 producing an estimated five to six tons. Latterly the deposit was worked, albeit for a very short period, for cobalt. Virtually the only silver mineral present is native silver, though EPMA detected minute grains of an unnamed silver-bismuth-selenide. Argentite has been reported but no specimens exist to confirm this. The native silver occurs as beautiful crystal dendrites up to 3Ýcm in length.
The most comprehensive account of mining is given by Meikle in the Journal of the Russell Society. The deposit was discovered in 1606 and production ceased in 1616 although in the 1750s, nickeline (NiAs), previously discarded by the miners, was recovered from the surface dumps and sold. The deposit is found alongside a quartz dolerite dyke intruded into Lower Limestone Group Carboniferous sedimentary and volcanic strata. Two distinct metallogenic assemblages have been identified, only one of which contains silver. Few specimens from the deposit exist today. From the literature (Aitkinson, 1619) it appears that the native silver occurred as wire silver:
the manner how it grew was like unto the haire of a manís head and the grasse in the fielde.
Meikleís work revealed the presence of two other silver minerals: acanthite (Ag2S), and amalgam (Ag,Hg). The deposit was exceptionally rich and equally as short lived.
The naturally occurring silver halide minerals, chlorargyrite (AgCl), bromargyrite (AgBr) and iodargyrite (AgI) (no problem about working out how these minerals got their names) exhibit light sensitive properties. The reaction of silver halides to light spawned the greatest use of silver today, such that 40% of the silver mined is used in the photographic industry. A common use in the past for silver was to make coins, but today, only six percent of the worldís silver is used for coinage. Another use for the metal is the silvering of mirrors. Silver is used to coat smooth glass surfaces by vaporisation of the metal or by precipitation from a solution, though today, aluminium has largely replaced silver in this process. Silver is also used in the manufacture of switches, printed circuits, long-lasting batteries and bearing alloys for aeroplanes, diesel engines and some motor cars. When alloyed with copper, silver is used for welding. In its colloidal form, silver serves as a catalyst in the manufacturing of certain alcohols. When silver is alloyed with cesium, it is used in photocells and, in the form of silver iodide, it is used to seed clouds for weather modification purposes.