6 GO REPORT OF NATIONAL MUSEUM, 1897. 



Oxyfien salts, carhonatrs. — The carbonates — eoinpoiiiuls of carbon diox- 

 ide with other oxides — form a numerous and important class of minerals. 

 They may be conveniently arrani^ed as follows: Normal carbonates, 

 compounds in which the ratio of oxygen in the carbon dioxide to the 

 oxygen in the combined oxide is as 2:1; basic carbonates, compounds 

 in which the ratio of the number of the oxygen atoms to that of the 

 combined oxide is less than 2:1; fluo and chloro carbonates, compounds 

 in which there is a fluoride or chloride with a carbonate of the same 

 element. 



The following specimens are of this type: 



C'alcite— Waldshut, Germany. (Cat. No. 2016, U.S.N. M.) 



Smitbsonitc— Joplin, Missouri. (Cat. No. 48638, U.S.N. M.) 



Malachite— Nizne-Tagilsk, Siberia. (Cat. No. 49401, U.S.N. M.) 



Azurite — Copper Queen mine, Bisbee, Arizona. (Cat. No. 48769, U.S.N.M.) 



Phosgenite— Monte Toni, Sardinia. (Cat. No. 51948, U.S.N.M.) 



Oxygen salts, silicates. — The silicates — compounds of silicon oxides 

 with other oxides — constitute about nine-tenths of the known crust of 

 the earth and more than one-fourth of the known kinds of minerals. 

 Isomorphic combinations are the rule, and as a class they exliibit 

 great diversity of composition. For example, the ratio of oxygen in silica 

 to that in combined oxide may vary for monad and dyad elements, such 

 as potassium or calcium, between 2 : 4 and 4:1; and for silicates of triad 

 elements, such as aluminum or iron, between 2:6 and 12:3. Again, it 

 is not unusual to find a silicate containing both potassium and calcium 

 as oxides combined with silica, or the oxides of iron and aluminum, 

 or of calcium and aluminum, and that not necessarily in atomic pro- 

 portion. But, although certain oxides are capable of mutual replace- 

 ment in any and all proportions, such as the sesquioxides of iron, 

 aluminum, etc., or the monoxides of calcium, magnesium, iron, man- 

 ganese, sodium, lithium, etc., and though a silicate may contain at 

 once a mixture of sesquioxides and monoxides in combination with 

 silica, the place of a monoxide is not taken by a sesquioxide nor that 

 of a sesquioxide by a monoxide. 



Examples of this type are shown in the following specimens: 



Pj'roxene — Grasse Lake, St. Lawrence Countj', New York. (Cat. No. 48292, 

 U.S.N.M.) 



Hornblende— Wolfeberg, Bohemia. (Cat. No. 50604, U.S.N.M.) 



Beryl— Portland, Connecticut. (Cat. No, 81987, U.S.N.M.) 



Feldspar — Diana, Lewis County, New York. (Cat. No. 50876, U.S.N.M.) 



Garnet — Upland, Delaware County, Pennsylvania. (Cat. No. 51982, U.S.N.M.) 



Topaz— Stonebam, Maine. (Cat. No. 28915, U.S.N.M.) 



Calamine — Sterling Hill, Sussex County, New Jersey. (Cat. No. 14416, U.S.N.M.) 



Tourmaline — Macomb, St. Lawrence County, New Y'ork. (Cat. No. 48280, U.S.N.M.) 



Stilbite— Cape D'Or, Minas Basin, Nova Scotia. (Cat. No. 83415, U.S.N.M.) 



Muscovite — Chester County, Pennsylvania. (Cat. No. 83478, U.S.N.M.) 



Serpentine— Montville, New Jersey. (Cat. No. 47544, U.S.N.M.) 



Kaolin — Rio Francisco, Arizona. (Cat. No. 8879, U.S.N.M.) 



Genthite — Webster, Jackson County, North Carolina. (Cat. No. 44475, U.S.N.M.) 



