sb. pl. Mining. U.S. [Sp. tierras earths, pl. of tierra earth:—L. terra.] Pulverulent ore, spec. of quicksilver, mingled with sand and earthy matter; in Mexico, inferior pulverulent ores generally. Also attrib., as tierras-furnace, -ore.
1874. Raymond, Statist. Mines & Mining, 397. In 1865, the amount of ore worked was 15,974 tons of which the Tierras amounted to 1,955 tons…. Tierras yielded (estimated) 3 per cent., or 1,533 flasks. Ibid. (1877), 9. Number of tons tierras-ore roasted. Ibid., 17. A new tierras-furnace will take its place. Ibid. (1881), Mining Gloss., Tierras,… fine dirt impregnated with quicksilver ore, which must be made into adobes before roasting.
