According to the official records, there were registered in September 1906, 23,191 mining properties, of which very nearly five-sixths were described as producing s:'ver, either by itself or in combination with other metals: The properties were classed as 1572 gold, 5461 silver, 970 copper, 383 iron, 151 mercury, 94 lead, 86 sulphur, 52 antimony, 49 zinc, 40 tin, 21 opals, 9 manganese, 6 " sal gema," 5 tourmalines, i bismuth and i turquoise - the remainder being various combinations of these minerals. [Please select]
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Between the crossed tourmalines, I introduce a film of this crystal with its axis oblique to theirs. [Please select]
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When the tourmalines are crossed, the space where they cross each other is black. [Please select]
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Introducing between them a film of selenite, you observe that by turning the film round it may be placed in a position where it has no power to abolish the darkness of the superposed portions of the tourmalines. [Please select]
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