The colour of the well-known iron sulphide, pyrrhotite or pyrrhotine, is given in most treatises on mineralogy as 'bronze-yellow'. Dana calls it ' between bronze-yellow and copper-red ', and also notes that it is 'subject to speedy tarnish'. The accuracy of the last statement will not be doubted by any one who has had much acquaintance with mining operations in districts where pyrrhotite is a common lode mineral, but it does not appear to have been put on record in any scientific publication that the characteristic colour, not very accurately designated 'bronze-yellow', does not seem to be the original one of the unaltered mineral.