[5] Purum,—"pure." Interpretatio gives the German as gedigen,—"native."
[Pg 108][6] 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."
[7] The 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.
[8] Agricola 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.
Silver Minerals.
| Argentum purum in venis reperitur | Gedigen silber | *Native silver | |
| Argentum rude | Gedigen silber ertz | Rudis silver, or pure silver minerals | |
| Argentum rude plumbei coloris | Glas ertz | Argentite (Ag2S) | *Silver glance |
| Argentum rude rubrum | Rot gold ertz | Pyrargyrite (Ag3SbS3) | *Red silver |
| Argentum rude rubrum translucidum | Durchsichtig rod gulden ertz | Proustite (Ag3AsS3) | *Ruby silver |
| Argentum rude album | Weis rod gulden ertz: Dan es ist frisch wie offtmals rod gulden ertz pfleget zusein | White silver | |
| [Pg 109]Argentum rude jecoris colore | Gedigen leberfarbig ertz | Part Bromyrite (Ag Br) | Liver-coloured silver |
| Argentum rude luteum | Gedigen geelertz | Yellow silver | |
| Argentum rude cineraceum | Gedigen graw ertz | Part Cerargurite (Ag Cl) (Horn Silver) Part Stephanite (Ag5SbS4) | *Grey silver |
| Argentum rude nigrum | Gedigen schwartz ertz | *Black silver | |
| Argentum rude purpureum | Gedigen braun ertz | *Purple silver |
The last six may be in part also alteration products from all silver minerals.
The reasons for indefiniteness in determination usually lie in the failure of ancient authors to give sufficient or characteristic descriptions. In many cases Agricola is sufficiently definite as to assure certainty, as the following description of what we consider to be silver glance, from De Natura Fossilium (p. 360), will indicate: "Lead-coloured rudis silver is called by the Germans from the word glass (glasertz), not from lead. Indeed, it has the colour of the latter or of galena (plumbago), but not of glass, nor is it transparent like glass, which one might indeed expect had the name been correctly derived. This mineral is occasionally so like galena in colour, although it is darker, that one who is not experienced in minerals is unable to distinguish between the two at sight, but in substance they differ greatly from one another. Nature has made this kind of silver out of a little earth and much silver. Whereas galena consists of stone and lead containing some silver. But the distinction between them can be easily determined, for galena may be ground to powder in a mortar with a pestle, but this treatment flattens out this kind of rudis silver. Also galena, when struck by a mallet or bitten or hacked with a knife, splits and breaks to pieces; whereas this silver is malleable under the hammer, may be dented by the teeth, and cut with a knife."
Copper Minerals.