gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1968.036.282.16 Short Communications Quartz Twin on {303¯2} Frondel Clifford Department of Geological Sciences, Harvard University, Cambridge, Massachusetts 6 1968 36 282 861 864 23 2 1968 Copyright © 1968, The Mineralogical Society 1968