For at least the past thirty years a locality in Morocco has been producing strange mineralogical objects, objects that caught my fancy the first time I saw one (fig. 1). These are commonly referred to as pseudomorphs of quartz after crystals of an undetermined mineral or minerals, but they actually are perimorphs.* Perimorphs differ from pseudomorphs because they do not replace an earlier mineral; instead they form a mineral crust, usually quartz, over a preexisting mineral crystal (White 2003). In all of the examples from this Moroccan source the pre-existing mineral is now gone; it has been dissolved away, which means that one can only speculate as to what it might have been. In the case of the perimorphs described here, Amir C. Akhavan (http://www.quartzpage.de/; accessed March 2014) states that they likely are after fluorite. Although this might be true for those that are perfectly square, others are not quite square but have slightly acute angles. And there are others that are after a crystal that must have been a wafer-thin square plate (fig. 5).
John S. White, a consulting editor of Rocks & Minerals, operates Kustos, a museum/collector consulting business. Now retired, he is the former curator-in-charge of the National Mineral and Gem collection at the Smithsonian Institution.