Native Ore of Iridium

The ore of Iridium is found in brighter and flatted grains among the Peruvian Platinum, having an appearance of their having received some flattening blows from an hammer on a polished anvil, giving them a specular brightness. They are in general more or less irregularly angular, with their edges slightly worn; in colour almost as dark as Lead, by which, though very small, they are easily distinguished from the Platinum, Their hardness is so great, that they will scratch glass readily; they are brittle, dividing into flakes under the hammer; some of them retain the form of crystals but slightly rounded, which are hexaëdral tables, with their edges variously truncated or bevilled, the larger planes of which are smooth, and the lateral ones striated horizontally. They consist of Iridium alloyed by Osmium. These two metals were first discovered in the black powder that remains after dissolving crude Platinum, by Smithson Tennant, Esq, but the ore itself was first recognized by Dr. Wollaston, to whom we are indebted for the opportunity of figuring such large grains. The figures at the lower part of the plate are magnified.