Agricola, Georgius, De re metallica, 1912/1950

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              <s>
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              in gold mines, silver mines, or other mines; nor do other miners neglect them
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              if they are found in stone quarries, or in their own veins; their value is usually
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              indicated by their taste. </s>
              <s>Nor, lastly, does the miner fail to give attention to
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              the solidified juices which are found in metallic veins, as well as in their own
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              veins, from which he collects and gathers them. </s>
              <s>But I will say no more
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              on these matters, because I have explained more fully all the metals and
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              mineral substances in the books “
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              De Natura Fossilium.
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              ”</s>
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              <s>But I will return to the indications. </s>
              <s>If we come upon earth which is
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              like lute, in which there are particles of any sort of metal, native or
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              rudis,
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              the best possible indication of a vein is given to miners, for the metallic
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              material from which the particles have become detached is necessarily close
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              by. </s>
              <s>But if this kind of earth is found absolutely devoid of all metallic
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              material, but fatty, and of white, green, blue, and similar colours, they must
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              not abandon the work that has been started. </s>
              <s>Miners have other indications in
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              the veins and stringers, which I have described already, and in the rocks, about
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              which I will speak a little later. </s>
              <s>If the miner comes across other dry earths
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              which contain native or
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              rudis
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              metal, that is a good indication; if he comes
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              across yellow, red, black, or some other “extraordinary” earth, though it is
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              devoid of mineral, it is not a bad indication. </s>
              <s>Chrysocolla, or azure, or verdigris,
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              or orpiment, or realgar, when they are found, are counted among the good
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              indications. </s>
              <s>Further, where underground springs throw up metal we ought
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              to continue the digging we have begun, for this points to the particles having
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              been detached from the main mass like a fragment from a body. </s>
              <s>In the
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              same way the thin scales of any metal adhering to stone or rock are counted
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              among the good indications. </s>
              <s>Next, if the veins which are composed partly
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              of quartz, partly of clayey or dry earth, descend one and all into the depths
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              of the earth together, with their stringers, there is good hope of metal being
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              found; but if the stringers afterward do not appear, or little metallic
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              material is met with, the digging should not be given up until there is nothing
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              remaining. </s>
              <s>Dark or black or horn or liver-coloured quartz is usually a good
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              sign; white is sometimes good, sometimes no sign at all. </s>
              <s>But calc-spar,
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              showing itself in a
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              vena profunda,
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              if it disappears a little lower down is not a
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              good indication; for it did not belong to the vein proper, but to some stringer.
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              </s>
              <s>Those kinds of stone which easily melt in fire, especially if they are translucent
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              (fluorspar?), must be counted among the medium indications, for if other
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              good indications are present they are good, but if no good indications are
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              present, they give no useful significance. </s>
              <s>In the same way we ought to form
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              our judgment with regard to gems. </s>
              <s>Veins which at the hangingwall and
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              footwall have horn-coloured quartz or marble, but in the middle clayey
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              earth, give some hope; likewise those give hope in which the hangingwall
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              or footwall shows iron-rust coloured earth, and in the middle greasy and
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              sticky earth; also there is hope for those which have at the hanging or footwall
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              that kind of earth which we call “soldiers' earth,” and in the middle black
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              earth or earth which looks as if burnt. </s>
              <s>The special indication of gold is
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              orpiment; of silver is bismuth and
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              stibium;
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              of copper is verdigris,
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              melantería,
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              sory, chalcitis, misy,
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              and vitriol; of tin is the large pure black stones of </s>
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