PEALE.] MINEEALOGICAL APPENDIX. 453 



B. 



ANALYSES OF VOLCANIC BOCKS FROM YELLOWSTONE NATIONAL PARK. 



By William Beam, A. B. 



No. 1. Spherulitic obsidian. Collected by A. C. Peale, M. D. 



From tbe divide between Yellowstone Lake and Upper Geyser Basin of Fire Hole 

 River. 



Greenish-black masses, transparent in thin pieces. Hardness, 6 ; specific gravity, 

 2.4; fracture, conchoidal. Pyrology: Fusibility, 4. Heated strongly, it swells up to a 

 white blebby mass; with borax, gives a clear bead, and with microcosmic salt, a 

 skeleton of silica. 



COMPOSITION. 



Per cent. 



Si 0-2 77.00 



AlzOa+FCiOa 13.40 



CaO 1.25 



MgO 1.19 



K2O 3.62 



NaaO 3.43 



H2 O (by ignition) 70 



100. 59 



No. 2. A pebble of Quartz-trachyte, covered with a deposit from Echinus Geyser. 

 Collected by A. C. Peale, M. D. 

 A pebble about 1| inches in diameter, light fawn color, and containing particles of 

 clear silica. Texture, porous; rather friable; fracture, uneven; hardness, 3.5; spe- 

 cific gravity, 2.36. Pyrology: Nearly infusible; makes a clear bead with borax, and 

 with microcosmic salt, leaves a skeleton of silica. The powdered mineral is slightly 

 acted upon by hydrochloric acid. 



ANALYSIS. 



Per cent. 



SiOj 77.90 



A]203-fFe2 03 14.55 



CaO 40 



MgO Trace. 



K2O 4.63 



Na^O '. 2.10 



H2O (by ignition) 1.00 



100. 58 



The film of deposit from. Echinus Geyser is about one-eighth of an inch thick and 

 the interior of the pebble has probably undergone some change in composition by the 

 soaking of water into its substance. 



No. 3. Rock from Yellowstone Canon near falls. Collected by W. H. Holmes. 



Consists of white opaque fragments, rough to the touch ; fracture, conchoidal, rough; 

 texture, porous. Pyrology: Fusibility, 5.5; dissolves in borax to a clear bead, and 

 gives a skeleton of silica with microcosmic salt. Moistened with cobalt nitrate and 

 heated, it turns bright blue. The powdered mineral yields 14. G per cent, of its weight 

 to hydrochloric acid. 



ANALYSIS. 



Per cent. 



SiOij 64.60 



AI2O3-I- FeaO., 25.65 



MgO Trace. 



CaO Trace. 



K.O 0.76 



NajO 0.43 



H2O (by ignition) 8.70 



100. 14 



