As regards other kinds of metal, although some rich ores are found, still, unless the veins contain a large quantity of ore, it is very rarely worth while to dig them. The Indians and some other races do search for gems in veins hidden deep in the earth, but more often they are noticed from their clearness, or rather their brilliancy, when metals are mined. When they outcrop, we follow veins of marble by mining in the same way as is done with rock or building-stones when we come upon them. But gems, properly so called, though they sometimes have veins of their own, are still for the most part found in mines and rock quarries, as the lodestone in iron mines, the emery in silver mines, the lapis judaicus, trochites, and the like in stone quarries where the diggers, at the bidding of the owners, usually collect them from the seams in the rocks.[1] Nor does the miner neglect the digging of "extraordinary earths,"[2] whether they are found
- ↑ As stated in note on p. 2, Agricola divided "stones so called" into four kinds; the first, common stones in which he included lodestone and jasper or bloodstone; the second embraced gems; the third were decorative stones, such as marble, porphyry, etc.; the fourth were rocks, such as sandstone and limestone.
Lodestone. (Magnes; Interpretatio gives Siegelstein oder magnet). The lodestone was well-known to the Ancients under various names—magnes, magnetis, heraclion, and sideritis. A review of the ancient opinions as to its miraculous properties would require more space than can be afforded. It is mentioned by many Greek writers, including Hippocrates (460–372 b.c.) and Aristotle; while Theophrastus (53), Dioscorides (v. 105), and Pliny (xxxiv, 42, xxxvi 25) describe it at length. The Ancients also maintained the existence of a stone, theamedes, having repellant properties, and the two were supposed to exist at times in the same stone.
Emery. (Smiris; Interpretatio gives smirgel). Agricola (De Natura Fossilium., p. 265) says: "The ring-makers polish and clean their hard gems with smiris. The glaziers use it to cut their glass into sheets. It is found in the silver mines of Annaberg in Meissen and elsewhere." Stones used for polishing gems are noted by the ancient authors, and Dana (Syst. of Mineralogy, p. 211) considers the stone of Armenia, of Theophrastus (77), to be emery, although it could quite well be any hard stone, such as Novaculite—which is found in Armenia. Dioscorides (v. 166) describes a stone with which the engravers polish gems.
Lapis Judaicus. (Interpretatio gives Jüden stein). This was undoubtedly a fossil, possibly a pentremites. Agricola (De Natura Fosilium, p. 256) says: "It is shaped like an acorn, from the obtuse end to the point proceed raised lines, all equidistant, etc." Many fossils were included among the semi-precious stones by the Ancients. Pliny (xxxvii, 55, 66, 73) describes many such stones, among them the balanites, phoenicitis and the pyren, which resemble the above.
Trochitis. (Interpretatio gives spangen oder rederstein). This was also a fossil, probably crinoid stems. Agricola (De Natura Fosilium, p. 256) describes it: "Trochites is so called from a wheel, and is related to lapis judaicus. Nature has indeed given it the shape of a drum (tympanum). The round part is smooth, but on both ends as it were there is a module from which on all sides there extend radii to the outer edge, which corresponds with the radii. These radii are so much raised that it is fluted. The size of these trochites varies greatly, for the smallest is so little that the largest is ten times as big, and the largest are a digit in length by a third of a digit in thickness … when immersed in vinegar they make bubbles."
- ↑ The "extraordinary earths" of Agricola were such substances as ochres, tripoli, fullers earth, potters' clay, clay used for medicinal purposes, etc., etc.
| Silex ex eo ictu ferri facile ignis elicitur. . . . excubus figuris | Feldspar | *Feldspar | |
| Medulla saxorum | Steinmarck | Kaolinite | Porcelain clay |
| Fluores (lapides gemmarum simili | Flusse | Fluorspar | Fluorspar (see note 15, p. 380) |
| Marmor in metallis repertum | Spat | Barite | *Heavy spar |
Apart from the above, many other minerals are mentioned in other chapters, and some information is given with regard to them in the footnotes.
