Feldspar and Petuntse

Dr. Buchanan, whose researches in the East Indies are well known, brought me some of the Breccia Rock, from Callender in Scotland, in which I found pebbles of Feldspath. As Feldspar of this description has not, to my knowledge, been before noticed, I am pleased to have an opportunity of showing it here, where I have added some other amorphous Feldspar, known by the name of Petuntse in Scotland, found in various parts of the Pentland Hills, south-west of Edinburgh. This is of some esteem in manufactories of porcelain, being a fusible composition of Silex and Alumine, but varying in the proportion or quality. It often disappoints the workmen that gather it, as well as the manufacturers, and Quartz nearly pure has been sent to them as Petuntse, especially for the white or gray sort, which has least Iron, and would consequently be of most value for their purposes.