152 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Sulphur. — In small crystals on galenite from the Clifton Mine, near 

 Central ; found in Middle Park, Pagosa Springs. Sometimes found 

 in narrow seams in galenite, the result of decomposition of the latter. 



Sylvanite. — In the Eed Cloud Mine, of Gold Hill, occurring in foliated 

 masses and thread-like veins. In crystals and crystalline masses in 

 the Sunshine district. According to Professor Silliman* the ratio of 

 gold and silver for a specimen from the Red Cloud, is, gold 1.7 to 

 silver 1.0. Professor Genth publishes an analysis of sylvanite ob- 

 tained from the Eed Cloud Mine,t showing the following composi- 

 tion : 



Per cent. 



Qnartz 0.32 



Gold 24.83 



Silver 13.05 



Copper 0.23 



Zinc 0.45 



Iron 3.28 



Tellurium 56.31 



Selenium trace. 



Sulphur 1.82 



100. 29 



Talc. — In fine scales among the ganguerock of the Bobtail and Kan- 

 sas, near Central. In light pink scales in the Silver Hills and Barton 

 mines, Hardscrabble district. In Mosco Pass. 



Tellurite. — A new species described by Dr. Genth.f It is the result 

 of decomposition of tellurium and sellurides. Its formula is Te O2. 

 Found in the Keystone, Smuggler, and John Jay mines in small 

 crystals. 



Tellurium, native. — At the Eed Cloud Mine, of Gold Hill, in crys- 

 talline masses, belonging to the hexagonal system. The largest speci- 

 men known was obtained by Professor Schirmer from the Eed Cloud 

 Mine. It weighed about five pounds, and consisted in a mixture of 

 quartz and tellurium. Upon examination § it was found to contain 

 90.85 per cent, of tellurium, small quantities of selenium, iron, and 

 bismuth, and traces of gold and silver. Professor Silliman || did not 

 find any selenium. 



Genth publishes an analysis of tellurium from the Magnolia dis- 

 trict, Boulder County.^ 



Au 0.60 



Ag 0.07 



Te 96.91 



V2O3 0.49 



FeO 0.78 



Hg AI2 O3 Mg O Ka O, &c L 15 



100. 00 



Tennantite. — Crystals in Buckskin Gulch ; Geneva district ; Park 

 County. Ereeland Mine, Clear Creek County. 



TETRAHEDRiTE.^-Crystals in Buckskin Gulch. Fine crystals in the 

 Clifton lode, Central City. Crystals in the Colorado Chieftain lode, 

 San Juan district. Massive in a number of the San Juan silver- 

 mines. 



* Rep. U. S. Geol. Surv., 1873, p. 690, 



tProc. Am. Phil. Soc, Philadelphia, vol. xiv, p. 888, 1876. 



tZeitschr. fur Kryst. und Min, P. Groth, vol. ii, No. 1, p. 7, 1877. 



§ Compare Rep. U. S. Geol. Surv., 1873, p. 355. 



II Ibid., p. 685, and Am. Jour. Sci. xlii, p. 571. 



UZeitschr. fiir Kryst. und Min. P. Groth, vol. ii, No. 1, 1877. 



