542 ARSENIC. It seldom occurs massive; more frequently in crusts, and stalactitic. It is dull. The fracture is fine earthy It is opaque. It sometimes occurs in curved lamellar concretions. It is friable. Geognostic and Geographic Situation of the Species. _ It occurs at Andreasberg in the Hartz, along with na tive arsenic, red silver-ore, antimonial silver-ore, galena or lead glance, yellow-orpiment, and corroded quartz ; at Biber, along with siilphat of cobalt; at Joachimsthal with orpiment. It is also found at Gistain in the Pyrenees, and at Saint Marie aux Mines in France; and in the’ Island of Guadaloupe. Observations. It very much resembles Pharmacolith, with which, in deed, it has been often confounded. An obvious chemi cal character may be used for distinguishing them-—the oxide of arsenic is soluble in water, which is not the case with the pharmacolith. 5. Pharmacolite,