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BOOK V.
rudis', of yellowish green, yellow, purple, black, or outside red and inside
gold colour. These must be reckoned as the richest ores, because the gold
exceeds the stone or earth in weight. Next come all gold ores of which each
one hundred librae contains more than three unciae of gold7; for although but
a small proportion of gold is found in the earth or stone, yet it equals in value
other metals of greater weight.8 All other gold ores are considered poor, because
'Rudis,—" Crude." By this expression the author really means ores very rich in
any designated metal. In many cases it serves to indicate the minerals of a given metal, as
distinguished from the metal itself. Our system of mineralogy obviously does not afford an
acceptable equivalent. Agricola (De Nat. Foss., p. 360) says: " I find it necessary to call
" each genus (of the metallic minerals) by the name of its own metal, and to this I add a
" word which differentiates it from the pure (puro) metal, whether the latter has been mined
" or smelted ; so I speak of rudis gold, silver, quicksilver, copper, tin, bismuth, lead, or iron.
" This is not because I am unaware that Varro called silver rudis which had not yet been
" refined and stamped, but because a word which will distinguish the one from the other is
" not to be found."
7The reasons for retaining the Latin weights are given in the Appendix on Weights
and Measures. A centumpondium weighs 70.6 lbs. avoirdupois, an uncia 412.2 Troy
grains, therefore, this value is equal to 72 ounces 18 pennyweights per short ton.
8Agricola mentions many minerals in De Re Metallica, but without such description
as would make possible a hazard at their identity. From his De Natura Fossilium, however,
and from other mineralogies of the 16th Century, some can be fully identified and others
surmised. While we consider it desirable to set out the probable composition of these
minerals, on account of the space required, the reasons upon which our opinion has been based
cannot be given in detail, as that would require extensive quotations. In a general way, we
have throughout the text studiously evaded the use of modern mineralogical terms—unless
the term used to-day is of Agricola's age—and have adopted either old English terms of
pre-chemistry times or more loose terms used by common miners. Obviously modern
mineralogic terms imply a precision of knowledge not existing at that period. It must not
be assumed that the following is by any means a complete list of the minerals described by
Agricola, but they include most of those referred to in this chapter. His system of mineralogy we have set out in note 4, p. 1, and it requires no further comment here. The
grouping given below is simply for convenience and does not follow Agricola's method. Where
possible, we tabulate in columns the Latin term used in De Re Metallica; the German equivalent given by the Author in either the Interpretatio or the Glossary; our view of the probable
modern equivalent based on investigation of his other works and other ancient mineralogies,
and lastly the terms we have adopted in the text. The German spelling is that given in the
original. As an indication of Agricola's position as a mineralogist, we mark with an asterisk
the minerals which were first specifically described by him. We also give some notes on
matters of importance bearing on the nomenclature used in De Re Metallica. Historical notes
on the chief metals will be found elsewhere, generally with the discussion of smelting methods.
We should not omit to express our indebtedness to Dana's great " System of Mineralogy,"
in the matter of correlation of many old and modern minerals.
Gold Minerals. Agricola apparently believed that there were various gold
minerals, green, yellow, purple, black, etc. There is nothing, however, in his works that
permits of any attempt to identify them, and his classification seems to rest on gangue
colours.
