Diamonds and precious stones, a popular account of gems .. . sand varieties of rocks knownunder the name oi jaspers. These varieties, hardenough to cut glass, present wide bands of diversecolours, generally red and green, upon a brownground. The silicious element predominates in the jas-pers, but with it is associated certain bases (alumina,oxide of iron, &c.), sufficient to render the wholefusible under the flame of the ordinary blowpipe,which is not the case with quartz or its varietiesthat are very nearly pure. The substances known in commerce under thename of jaspers diffisr so greatly fro
Diamonds and precious stones, a popular account of gems .. . sand varieties of rocks knownunder the name oi jaspers. These varieties, hardenough to cut glass, present wide bands of diversecolours, generally red and green, upon a brownground. The silicious element predominates in the jas-pers, but with it is associated certain bases (alumina,oxide of iron, &c.), sufficient to render the wholefusible under the flame of the ordinary blowpipe,which is not the case with quartz or its varietiesthat are very nearly pure. The substances known in commerce under thename of jaspers diffisr so greatly from each otherthat their price varies from 20c. to $12 the pound. ENGRAVING UPON AGATE, &C. It is the agate, and the varieties of which it is thetype, that have in all ages furnished to the engraverthe stones best suited to his art. ENGRAVING UPON AGATE. 169 One of the most remarkable engravings uponagate, and one of the finest specimens of this stone,is represented by Fig. 74. It is the bust of Alex-ander the Great. The head is carved in relief, and. Fig. 74.—^Agate, Alexander the Great (reduced to three-quarters), its colour is quite different from that of the ground-work of the stone. It is set in a superb frame ofenamelled gold. I70 PRECIOUS STONES. The fig. following (Fig. 75) is a chalcedony dis-playing a bacchic bull with an ivy wreath aroundhis body and a thyrsus under his feet. It is one ofthe most celebrated of antique engraved gems, andbears the signature of the famous graver Hyllus. As a specimen of modern engraving, we representby Fig. y6 that celebrated stone known as the sealof Michael Angelo. It is a small transparent cor-nelian engraved en creux or entaille. In the small
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectgems, booksubjectprec
