PRELIMINARY HANDBOOK OF THE DEPARTMENT OF GEOLOGY. 43 



Under the head of non-metallic minerals are shown a variety of useful 

 mineral substances, including sulphur, the salts used in chemical man- 

 ufacture, gypsum, grinding and polishing materials, asbestus and its 

 application, miueral fertilizers, fictile materials, and the natural carbon 

 compounds, as already noted. 



It is not necessary to go into greater descriptive detail here regard- 

 ing this series, as refereuce can be made to the handbook above men- 

 tioned. The following summaries are from a previous publication on 

 the condition of the department 1 . Changes and additions since made 

 have necessitated numerous alterations. 



A— METALLIC MIXEKALS. 



The mineralogy of gold is illustrated by 29 specimens. Of these, 28 

 represent free gold, and one sylvanite. Of the free golds 10 represent 

 placer gold. 



This series begins with a well-crystallized specimen that is only 

 slightly water- worn, and continues through various degrees of rounding 

 to a well-worn nugget, weighing an ounce. Fifteen specimens represent 

 quartz gold, beginning with crystals in a cavity in fresh quartz, and 

 following through various steps of crystallization of the gold and de- 

 composition of the matrix to a natural alloy of gold and silver in wholly 

 decomposed material. 



Two specimens of crystallized auriferous pyrite represent sulphuret 

 gold, and a single specimen represents auriferous slate. 



The gold ores are divided into placer, quartzose, sulphuret, telluride, 

 and fusion ores. Beside the placer golds in the mineral series, 5 speci- 

 mens illustrate hydraulic gravels, varying from characteristic samples 

 to a very rich specimen containing several flakes of visible gold; 9 

 specimens, in addition to the quartz gold in the mineral collection, illus- 

 trate quartzose ores. These begin with very pure white quartz and 

 follow through increasing amounts of other minerals, particularly sul- 

 phides in the quartz, to specimens containing large amounts of pyrite, 

 chalcopyrite, galena, and blende. The quartzose ores graduate insen- 

 sibly into the sulphuret ores, and the two really form one series. 



The 10 sulphuret ores begin with pyrite and quartz and run through 

 to pure sulphides; decomposed sulphides follow, and the series closes 

 with 2 specimens of mispickle. Five specimens illustrate the telluride 

 ores from Boulder County, Colorado. 



The extraction of gold from its ores is illustrated by 3 collections, 

 The operation of the hydraulic process is illustrated by 9 specimens 

 from the North Bloomfield gravel mine, California; the stamping and 

 amalgamating of sulphuret ores by 7 specimens from the Bobtail mill, 

 Blackhawk, Colorado, and the extraction of gold, silver, and copper in a 

 complex operation by 15 specimens from Balbach's Newark Smelting 



•Tin- Departmenl of Metallurgy and Economic Geology in the U. S. National 

 Museum, by I\ P. Dewey, Trans. Am. Inst, Engineers, Vol. xix, 18U0. 



