656 REPORT OF NATIONAL MUSEUM, 1897. 



Tyrolite—Cu5(OH),A8..0».7HeO— Mammoth mine, Tiutic, Utah. (Cat. No. 4812, 



U.S.N.M.) 

 Chukauthite— CuS0^.5H,^0— Copiai.o, Chile. (Cat. No. 12621, U.S.N.M.) 

 Brochantite — Cu.i(OH)iiSOi — Mammoth mine, Tiutie, Utah. (Cat. No. 48111, 



U.S.N.M.) 



Silver and its combinations. — Silver, alone or with other elements, 

 combines with sulphur, selenium, tellurium, arsenic, and antimony to 

 form compounds, of which the following are examples : Argeutite, AgaS, 

 naumannite, Ag.Se; hessite, AgjTe; huntilite, Ag:,As; dyscrasite,Ag:iSb; 

 proustite, AguAsS;,, and pyrargyrite, AgsSbS.-,, United with chlorine, 

 bromine, or iodine it forms the minerals cerargyrite, AgCl; bromyrite, 

 AgBr, and iodyrite, Agl. It does not unite witli oxygen, and hence 

 forms no oxygen compounds. 



Examples. 



Argeutite — AgnS — Himmelsfiirst iiiiue, Freiberg, Saxony. (Cat. No. 49505, U.S. 

 N.M.) 

 Stromeyerite—(Ag,Cu).>S— Altai, Siberia. (Cat. No. 49426, U.S.N.M.) 

 Dystrasite—AgaSb— Cornwall, Euglaud. (Cat. No. 169-52, U.S.N.M.) 

 Huntilite— AgsAs— Isle Royale, Lake Superior. (Cat. No. 49354, U.S.N.M.) 

 Miargyrite—AgSbSj -Saxony. (Cat. No. 42425, U.S.N.M.) 

 Stephanite — AgioSbiS^ — Reese River, Nevada. (Cat. No. 15133, U.S.N.M.) 

 Proustite— Ag:iAsS:!—Batopela8, Chihuahua, Mexico. (Cat. No. 81291, U.S.N. i^I.) 

 ryrargyrite—Ag.jSbS:,— Bolivia. (Cat. No. 49887, U.S.N.M.) 

 Cerargyrite— AgCl— Lake A\illey, New Mexico. (Cat. No. 47086, U.S.N.M.) 

 Bromyrite— AgBr— Broken Hill mine, New South Wales. (Cat. No. 512G3, U.S.N.M.) 

 lodyrit. — Agl— Chauarciilo, Chile. (Cat. No. 1,S017, U.S.N.M.) 



Gold and its combinations. — Gold is, with a few exceptions, found only 

 in tlie native state, sometimes pure, but more often alloyed with silver 

 or intimately mixed with other metallic elements or their compounds. 

 In nature it combines with but one negative element, tellurium, forming 

 the compounds sylvauite, (Au,Ag)Te2 5 n^igyagite, AuaPbi4Sb3(S,Te)24, 

 and petzite, (Au,Ag)Te. 



Examples. 



Sylvanite— (Au,Ag)Te,— P.oukler County, Colorado. (Cat. No. 81145, U.S.N.M.) 

 Petzite — (Au,Ag)/re — Sunshine district, Boulder County, Colorado. (Cat. No. 

 9723, U.S.N.M.) 



TYPES OF MINERALS. 



Tiie combinations of the several elements, together with such elements 

 as may occur free, fall naturally in two classes — elements and comjiounds. 



By a compound is meant that body produced by the combination of 

 two or more elements, and which is different in its nature from, and 

 whose properties as a rule are not the mean of, those of its constituents. 

 A compound is to be distinguished from a mixture, or simple mechan- 

 ical aggregation, in that it always implies a chemical union of its com- 

 ponents, and therefore possesses a definite chemical composition. 



Among minerals these two classes may be further divided in accord- 



