824 ^^^^ POPULAR SCIENCE MONTHLY, 



flat plate-glass cxbibition-cases, the gems being neatly marked with 

 printed labels, and arranged on velvet pads with a silk-rope border. 

 The diversity, brilliance, and richness of Nature's brightest colors dis- 

 played render the whole effect a very attractive and pleasing one. 

 The collection begins with a suite of glass models of the historical 

 diamonds, followed by a series of diamonds in their natural state, 

 among which is an interesting octahedron, eighteen carats in weight.* 

 These specimens are good illustrations of the form from South Africa, 

 though of little commercial value as gems. One dozen other crystals 

 from one quarter to one carat in weight complete a representative set 

 of form and occurrence in that region. Next we have a very neat set 

 of a dozen more crystals, small but choice, principally from India and 

 Brazil, and formerly belonging to the Mallet collection. One of 

 these is a perfect cube, a form peculiar to Brazil, while another is 

 twinned parallel to the octahedron. Another stone of one carat is 

 only half cut, and for comparison we have a stone of about the same 

 weight completely cut. 



Among the sapphires we find a carat, oblong stone of dark-blue 

 color, from the Jenks mine, Macon County, North Carolina, which has 

 yielded a few fair sapphires, yellow, violet, and blue, and a few rubies, 

 some of the finest of which were in the Leidy collection ; also the first 

 stones found here, the dark-brown, asteriated sapphires, described 

 in "Transactions of the New York Academy of Sciences," March, 

 1883, and two other cut stones weighing from four to eight carats. 

 These all show a slight bronze play of light on the dome of the cabo- 

 chon in ordinary light, but under artificial light they all show well- 

 defined stars, being really asterias or star-sapphires, and not cat's-eyes, 

 as would seem at first glance. There are also two cut stones, light 

 blue and light green, weighing one and two carats res2:)ectively, which, 

 for light-colored sapphires, are perhaps, when cut, brighter than those 

 from any other locality. The cutting of one of these gems has given 

 it a remarkable luster. They are found in the sluice-boxes at and 

 near Helena, Montana. Following are two broken crystals of the dark- 

 green sapphires from the quite recent find at the Hills of Precious 

 Stones in Siara, beautifully dichroitic, being green and blue when 

 viewed in different axes. An asteria of good blue color, measuring 

 nearly one inch across, a beautiful two-carat ruby-asteria, and a small 

 three-quarter-carat ruby, of fair color, complete the corundum gems. 



* Gems arc generally bought and sold by the weight, called a carat, which is equal to 

 about 3"1C8 troy grains. It is usually divided, however, into four diamond or pearl 

 grains, each of which is •7925 of a true grain. Fractions of a carat are also known as 

 fourths, eighths, sixteenths, thirt_v-second3, and sixty-fourths. The weight of the carat 

 formerly differed slightly in different countries, and this diversity finally led a syndicate 

 of Parisian jewelers, goldsmiths, and gem-dealers, in 1871, to propose a standard carat. 

 This was subsequently confirmed by an arrangement between the diamond-merchants of 

 London, Paris, and Amsterdam, fixing the uniform value of the diamond (?) carat at '205 

 grain. 



