copperas
/ˈkɒp(ə)rəs
/noun [mass noun]
Green crystals of hydrated ferrous sulphate, especially as an industrial product.These knobbly, metallic-looking fossils were turned into a mixture of dilute sulphuric acid and dissolved copperas using a dangerous, complicated and highly noxious industrial process....
- An inventory of Okeman's works near Poole in Dorset, dated November 1583, records 55 hogsheads of copperas, along with the equipment for manufacturing alum and copperas.
- Removal of large amounts of ordinary cave sediment may indicate saltpeter or fertilizer mining, while gypsum, copperas, alum, or Epsom salt are usually indicated by crystalline or powdered white, yellow, or green deposits.
Origin
Late Middle English coperose, from Old French couperose, from medieval Latin cuperosa, literally 'flower of copper', from late Latin cuprum (see copper1) + rosa 'rose', translating Greek khalkanthon.