182 Decomposition of Iron Pyrites. 



No. 7. Pyrite. Adorf, Saxony. Groups of sharply defined 

 cubes, faintly striated ; ondrusy rhomboliedra of calcite, in cav- 

 ities of a red hematitic calcareous schist. The crystals are pale 

 brass-yellow and splendent, and possess a very minutely compos- 

 ite scaley structure, sometimes rendering the surface fibrous. 

 Also rare octabedra. Decomposition : a bright yellow tarnish 

 on many faces. 



No. 8. Pyrite. Alabama, Genesee County, New York. 

 Flattened striated cubes, with sharp edges, and solid angles 

 modified by faces of the octahedron ; pale brass-yellow and 

 splendent on fracture. Decomposition: on the outer surface, a 

 brownish black shining enamel of hard compact limonite, a 

 mere film ; but often with soft iron ochre, earthy and orange- 

 yellow, sometimes to the depth of 3 mm. 



No. 9. Limonite, pseudomorphous after pyrite. Dutchess 

 County, New York. Sharp, shining striated cubes, unmodified, 

 consisting entirely of limonite. Color reddish brown, with ad- 

 hering crusts of soft brownish yellow limonite ochre. 



No. 10. Pyrite. Gilpin County, Colorado. A light yellow- 

 ish and brilliant aggregate of small crystals ; in a granular 

 matrix of pyrite, with a little white quartz. The mineral has 

 been found auriferous, 110 per ton. The crystals consist of 

 pyritobedra, tetrakishexahedra, and striated cubes with angles 

 modified by planes of the icositetrahedron ; fresh fracture, pale 

 brass-yellow, splendent, and sub-conchoidal. Decomposition : 

 no traces visible in the specimen. 



No. 11. Pyrite. Gilpin County, Colorado, A coarser crys- 

 talline mass, with geodes of large striated cubes like those of 

 No. 10, but unmodified and splendent like those of No. 95. De- 

 composition : no trace visible in the specimen. 



No. 12. Pyrite. Galena, Illinois. A crust upon a nodule 

 of marcasite, already described (See Nos. 23 and 24 of the latter 

 mineral). The coarse fibres terminate, at the exterior of the 

 nodule, in a bright bronze-yellow surface, drusy with splendent 

 crystals of pyrite, iridescent foliated cubes with all their faces 

 curved, arranged in continuous rows, and so producing a kind 

 of striation upon the surface ; within the nodule, the cubes are 

 flat-faced, with octahedral modifications; with sphalerite in 

 drusy cavities. Decomposition: a brass-yellow tarnish; the 



