536 REPORT OF NATIONAL MUSEUM, 1900. 



Vesuvanitc was first found in the ancient Vesuvian lavas, and in the 

 dolomite of Monte Sonina. It occurs rather al^undantly in g-ranular 

 limestone, serpentine, chlorite schist, gneiss, etc., frequentl}^ as a result 

 of contact metamorphism. Its common associates are garnet, diopside, 

 epidote, wollastonite, and titanite. 



The name vesuvianite is from the first known ]ocalit3\ Idocrase is 

 from siSog^ I see, and Kpaaiz^ '})iixtare, in allusion to the resemblance 

 between its form and those of other minerals. Cyprine is the name 

 applied to a pale blue kind occurring near Tellemarken, Norway. 



One hundred parts of vesuvianite contain approximately^: Silica, 

 39.6; alumina, 22.5; lime, 32.6; iron, 5.3. 



WILLEMITE. 



Anhydrous silicate of zinc has a hardness of 5.5; a specific gravity of 

 3.9; and a vitreo-resinous luster. Sufficiently transparent specimens 

 afl'ording fair cabinet gems have been found at Franklin, Sussex 

 County, New Jerse3^ The color varies from golden or greenish yel- 

 low, near that of chrysoberyl, to a canary-yellow. The mineral is 

 commonly opaque and of a brown, apple-green, or flesh-red color, and 

 at Franklin is usually mixed with zincite and franklinite. 



ZIRCON. 



HYACINTH — JACINTH — JARGON. 



Zircon crystallizes in the tetragonal system, occurring commonly in 

 square prisms; also in irregular forms and grains. Its hardness is 

 7.5; specific gravity, commonly 4.7, sometimes as low as 4.2, or as 

 high as 4.86; luster, adamantine; double refraction, strong. Its range 

 of color includes green, red, brown, blue, yellow, all presenting many 

 gradations of hue, to colorless. Its "fire" is second only to that of 

 the diamond, and this, together with its brilliant luster and range of 

 rich and delicate tones of color, makes it an attractive gem. 



The zircon includes the gems known as hyacinth, or jacinth and jar- 

 gon or jargoon. The hyacinth includes the reddish, brownish, and 

 orange-red specimens; the jargon the yellowish, smoky, and colorless 

 kinds. 



Zircon occurs in crystalline rocks such as granular limestone in 

 gneiss, granite, and syenite; in chlorite and other schists, and in allu- 

 vial deposits derived from them. 



Chemically it contains in 100 parts; Zirconia, 67.2; silica, 32.8. 



