There is another sort of black ore, in which the silver does not at all appear; and which, when wetted and rubbed against iron, becomes red. This ore is called _rosicler_, signifying that ruddiness which appears at the dawn of day. This is very rich, and affords the finest silver. Another kind, called _zoroche_, glitters like talc, and is generally very poor, yielding little silver: Its outer coat is very soft and of a yellowish red, but seldom rich; and the mines of this sort are wrought on account of the easiness of extracting the ore, being very easily dug. Another kind, not much harder than the last, is of a green colour, called _cobrissa_ or copperish, and is very rare. Although the silver usually appears in this kind, and it is almost mouldering, it is the most difficult of all to manage, as it parts very difficultly with the silver. Sometimes, after being stamped or reduced to powder, it has to be burnt in the fire, and several other expedients must be used to separate the silver, doubtless because mixed with copper. There is another very rare sort of ore, which has only been found in the mine of _Cotamiso_ at Potosi, being threads of pure silver entangled, or wound up together, like burnt lace, and so fine that it is called _arana_, or spider ore, from its resemblance to a cobweb.
The veins of _mineray_, of whatever sort they may be, are generally richer in the middle than towards the edges; and where two veins happen to cross each other, the place where they meet is always very rich. It is also observed that those which lie north and south are richer than those which lie in any other direction. Those also which are near to places where mills can be erected, and can consequently be more commodiously wrought, are often preferable to others that are richer, but require more expense in working. For this reason, at Lipes and Potosi, a chest of ore must yield ten marks or eighty ounces of silver, to pay the charges of working; while those in the province of Tarama only require five merks or forty ounces to defray the expences. When even very rich, and they happen to sink down so as to be liable to be flooded, the adventurers must have recourse to pumps and machines in order to drain them; or to _cocabones_ or levels dug through the sides of the mountain, which often ruin the owners by the enormous expence they are insensibly drawn into. At some of the mines, where the methods of separation already described fail, they use other means of extracting the silver from the ore, and from other metals which may be combined with it; as by fire, or strong separating waters; and there the silver is cast into a sort of ingots, called _bollos_. But the most general and useful method is that already described.