Pyrite is an abundant mineral at the Falls of French Creek iron mine, and the remarkable elongated octahedral crystals formerly found there have been studied in detail by Penfield. These occurred embedded in calcite; and the majority of the crystals found in that association are simple octahedral in habit, with but rarely small faces of other forms. The crystals which occur implanted on the crusts of magnetite are, however, of an entirely different habit. In them the cube is dominant, but there are also prominent faces of a rather flat diploid, and smaller ones of many other modifying forms. The cube faces are usually curved, often decidedly wavy, and more or less dulled by etching. Reaching a maximum diameter of a centimeter or more, and occurring in groupings often thickly scattered over the brilliant black magnetite, these pyrites yield striking mineral specimens, and they seem worthy of description, even though they show no new nor even unusual forms for the mineral.

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