652 REPORT OF NATIONAL MUSEUM, 1897. 



oxygen and iron containing water. Sometimes the comma or the sign + 

 is used in i^lace of the period. Further, the letter R is used to denote 

 a varying group of equivalent elements. Thus, It Cb20 ; is a compound 

 in which there is a varying amount of the equivalent elements of the 

 rare earths. R is also used as a general symbol for anj' element. These 

 general principles are illustrated by the following series of labels and 

 specimens showing the combinations of some typical elements: 



Zinc and its covtbinations. — Zinc combines with sulphur to form the 

 comi)ouuds sphalerite, and wurtzite. Combined with oxygen it forms 

 the compound ziucite; with oxygen and other elements it forms a num- 

 ber of combinations. These oxygen compounds may be either oxida- 

 tion products of zinc compounds alone, such as goslarite, ZnSOi.THiO; 

 adamite, Zn2(OH)As04; and smithsonite, ZnCO;,; or of zinc compounds 

 in which there is some other base, as in kottigite (Zn,Co);iAs20H.8H20, 

 and aurichalcite (Zu,Cu)5(OH),j(C03)2. Zinc combines with silicon and 

 oxygen to form two well-defined compounds, willemite, Zn2Si04, and 

 calamine, H2Zn2Si04. 



Examples. 



Sphalerite — ZnS — Wheatle^ miDe, Phcenixville, Pennsylvania. (Cat. No. 81829, 



U.S.N.M.) 

 Wurtzite— ZnS— Przibram, Bohemia. (Cat. No. 51476, U.S.N.M. ) 

 Zincite — ZnO — Franklin, Sussex County, New .Jersey. (Cat. No. 83614, U.S.N.M.) 

 Smitbsonite— ZnCOa- Altenherg, Belgium. (Cat. No. 51530, U.S.N.M.) 

 Aurichalcite — fZn,Cu)5(OH)fi(C03)2 — Emi)ire mine, .Jopliu, Missouri. (Cat. No. 



82198, U.S.N.M.) 



Willemite — Zn2Si04 — Franklin, Sussex County, New .Jersey. (Cat. No. 83615, 



U.S.N.M.) 

 Calamine — H^Zn^SiOj — Sterling, Sussex County, New Jersey. (Cat. No. 81954, 



U.S.N.M.) 

 Descloizite — (Zn.Pb).(0H)V04 — Commercial mine, Georgetown, New Mexico. 



(Cat. No. 48460, U.S.N.M.) 

 Adamite— Zn2(OU)As04—Laurium, Greece. (Cat. No. 48520, U.S.N.M.) 



Tin and its combinations. — Tin occurs in combination with sulphur 

 along with copper and iron in stannite, and with oxygen in cassiterite. 

 These compounds, together with a few minerals in which the stannic; 

 comjiounds have been occluded and are present only as an impurity, 

 are the only known occurrences of this element. 



Examples. 



Stannite— Cu.FeSnS^— St. Just, Cornwall, England. (Cat. No. 47028, U.S.N.M.) 

 Cassiterite — SnO.. — Grauien, Bohemia. (Cat. No. 4.5607, U.S.N.M.) 



Lead and its combinations. — Lead unites with sulphur alone to form 

 galena, and with sulphur and arsenic or antimony to form a number of 

 compounds, of which dufrenoysite, Pb2As2S.-,, and zinkenite, PbSbaSj, 

 are examples. Combined with selenium or tellurium it is found iu 

 clausthalite, PbSe, and altaite, PbTe. It forms a number of combina- 

 tions with oxygen. These oxygen compounds may be simple oxidation 

 products of lead alone, such as massicot, PbOj i)lattnerite, Pb02, and 



