Account of a Discovery of Native Minium

XI. *Account of a Discovery of native Minium.* In a Letter from James Smithson, Esq. F. R. S. to the Right Hon. Sir Joseph Banks, K. B. P. R. S. Read April 24, 1806. MY DEAR SIR, I beg leave to acquaint you with a discovery which I have lately made, as it adds a new, and perhaps it may be thought an interesting, species to the ores of lead. I have found minium native in the earth. It is disseminated in small quantity, in the substance of a compact carbonate of zinc. Its appearance in general is that of a matter in a pulverulent state, but in places it shows to a lens a flaky and crystalline texture. Its colour is like that of factitious minium, a vivid red with a cast of yellow. Gently heated at the blowpipe it assumes a darker colour, but on cooling it returns to its original red. At a stronger heat it melts to litharge. On the charcoal it reduces to lead. In dilute white acid of nitre, it becomes of a coffee colour. On the addition of a little sugar, this brown calx dissolves, and produces a colourless solution. By putting it into marine acid with a little leaf gold, the gold is soon intirely dissolved. When it is inclosed in a small bottle with marine acid, and a little bit of paper tinged by turnsol is fixed to the cork, the paper in a short time entirely loses its blue colour, and becomes white. A strip of common blue paper, whose colouring matter is indigo, placed in the same situation undergoes the same change. The very small quantity which I possess of this ore, and the manner in which it is scattered amongst another substance, and blended with it, have not allowed of more qualities being determined, but I apprehend these to be sufficient to establish its nature. This native minium seems to be produced by the decay of a galena, which I suspect to be itself a secondary production from the metallization of white carbonate of lead by hepatic gas. This is particularly evident in a specimen of this ore which I mean to send to Mr. Greville, as soon as I can find an opportunity. In one part of it there is a cluster of large crystals. Having broken one of these, it proved to be converted into minium to a considerable thickness, while its centre is still galena. I am, &c. JAMES SMITHSON. Cassell in Hesse, March 2d, 1806.