gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1882.005.22.05 IV.—On Some Artificial Forms of Silica, Illustrative of the Structure of Agates, Chalcedonies, etc. I'Anson J. F.G.S. Pankhurst E. A 2 1882 5 22 34 40 Copyright © 1882, The Mineralogical Society 1882