22 ROGERS— NOTES ON PSEUDOMORPHS, [February 4, 



Alterations. 



24. Sulfur from Sphalerite. — Galena, Kansas. Specimens of 

 sphalerite and pyrite in chert breccia from the Templar ground, 

 two miles southwest of Galena. Kan., show in an excellent manner 

 the alteration of a sulfid to sulfur. The sphalerite is corroded and 

 covered with pale yellow sulfur while the pyrite is fresh and free 

 from sulfur. Evidently the sphalerite has furnished the sulfur. 



25. Strontianite from Celestite. — Five miles from Austin, Texas, 

 on the road between Mts. Barker and Bonnell. Collected by Mr. 

 F. L. Hess. Massive cleavable celestite of a pale blue tint is much 

 corroded and the cavities are occupied by tufts of small acicular 

 crystals of strontianite. The crystals are flattened, tapering, six- 

 sided crystals, the forms being a steep rhombic bipyramid (hhl) and 

 a steep rhombic prism (okl). The crystals are often curved and 

 in consequence give a wavy extinction. The elongation is parallel 

 to the faster ray. The mineral contains some calcium in addition 

 to strontium as the microchemical g}'psum test shows. This is the 

 best test for calcium in such a compound. 



26. Barite from Witherite. — Northumberland, England. Color- 

 less tabular barite crystals {001, no, 102) are found in cavities of 

 massive gray witherite. The barite is evidently a secondary product, 

 formed from the witherite. 



2j. Copiapite from Pyrite and Liinonitc from Copiapite. — Five 

 miles n. w. of San Jose, California. Altered pyrite crystals from 

 chlorite-glaucophane schist boulders showed the following cross- 

 section: The interior is hollow with small projecting bits of bright 

 pyrite. The exterior is limonite while between these two is a soft 

 compact yellow material which answers the blowpipe tests for 

 copiapite. Under the microscope the copiapite is seen to consist 

 of minute pseudo-hexagonal crystals. Here the pyrite has evidently 

 altered to copiapite and then the latter to limonite. 



28. Hornblende from Hypersthene. — Arroyo Bayo, twelve miles 

 southwest of Livermore, California. These specimens were found 

 in a large outcrop of norite or hypersthene gabbro. Grayish green 

 hypersthene with faint cleavage has been altered around the borders 

 to black hornblende with good cleavage. In fragments the hyper- 



