EXHIBIT AT PAN-AMERICAN EXPOSITION. 221 



Each of these classes was preceded by a general label giving a short 

 statement of its more important chemical characters, as illustrated by 

 the following- example: 



CLASS— SILK IATES. 



The silicates, derivatives of the several silicic acids H 4 Si0 4 , H 2 Si0 3 , H 6 Si 2 7 

 H 2 Si 2 5 , and H 4 Si 3 8 , or compounds of silicon oxide 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 the class 

 exhibits 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 potas- 

 sium 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, or the oxides of iron and aluminum, or of 

 calcium and aluminum, and that not necessarily in atomic proportion. But although 

 certain oxides are capable of mutual replacement in any ami all proportions, such 

 as the sesquioxide of iron or aluminum, or the monoxide of calcium, magnesium, 

 iron, manganese, sodium, or lithium; and though a silicate may contain at once a mix- 

 ture of sesquioxides and monoxides in combination with silica, the place of a monox- 

 ide is not taken by a sesquioxide, nor that of a sesquioxide by a monoxide. 



Following- the class label, arranged in order from left to fight, were 

 placed the several members of the class, selected to illustrate as com- 

 pletely as possible their occurrences, associations, and variety in form 

 and color. Each specimen was mounted on a block and accompanied 

 by a small label giving the name of the mineral, its associations, if 

 any, and its locality. 



Conspicuous among the several classes were the fluorides, carbon- 

 ates, silicates, and chromates, the individuals comprising them being 

 especially notable for their beauty and vivid coloring. Among the 

 fluorides were shown a magnificent series of German, English, and 

 American fluors having an extensive color range, including white, yel- 

 low, green, violet, sky. and amethystine blue, rose rod. and lilac. 

 Among the carbonates were the minerals malachite and azurite, the 

 former bright green in color, the latter a line Berlin blue. In addi- 

 tion a botryoidal mass of these two minerals was shown in which the 

 malachite and azurite are in alternate concentric layers, giving rise to 

 a strong and pleasing contrast of color. 



The display feature was well developed in the class silicates where 

 the green of microcline was contrasted with the rich blue of socialite. 

 Among the tourmalines was shown the cross section of a crystal red 

 internally, passing into a lighter hue, and finally green; there svas also 

 a line mass of ( alifornia rubellite of a delicate pink color on a ground- 

 mass of lilac-colored lepidolite. Play of color was well illustrated by 

 a fine cleavage mass of labradorite from Isle of Paul, in which blue 

 and green predominate. 



The series as a whole comprised some 500 specimens and 47 group 

 labels installed in 4 slope-top cases, as shown in Plates ;>.s and 59. 



