52(3 REPORT OF NATKJNAL MUSEUM, 1900. 



Sard. — A translucent, red, brownish red, blood red, golden or amber 

 colored chak-edony. Quartz crystals are occasionall}' met with which 

 are irridescent within, an effect due to fractures and cavities in the 

 interior. Such crystals are cut and sold under the name of iris. The 

 irised effect is frequently produced by artiffcial means, usually by heat- 

 ing- and then suddenly cooling the specimen. 



Quartz is widespread in its occurrence, being found in some of its 

 varieties in nearly every rock stratum. The varieties consist essen- 

 tially of either amorphous or crystalline silica in various forms, associ- 

 ated with various coloring compounds, such as those containing iron^ 

 manganese, or nickel. 



RHODONITE. 



FOWLERITE. 



Rhodonite has a hardness of r),5, a specific gravity of 3.6, and a 

 vitreous luster. The kinds used as ornamental stones are a fine rose 

 to flesh red, often streaked with Ijlack. Though somewhat soft, the 

 mineral is nearlj^ as tough as jade. The variety known as fowlerite 

 occurs in fine flesh-red crystals, some of them over 4 inches thick, at 

 Franklin, Sussex County, New Jerse}'. 



Rhodonite contains: Silica, 4.5.9; manganese oxide, 54.1. 



RUTILE. 



Rutile occurs crj'stallized and massive. The crystals are frequently 

 acicular; often geniculated, and usually have their vertical planes 

 striated. Hardness, 6 to 6.5; specific gravity, 4.25; luster, metallic 

 adamantine; color, reddish browni passing into red, black, yellowish, 

 violet, blue, and occasionally green. The black variety, nigrine, more 

 closely approaches the black diamond in appearance than any other 

 gem. The reds have the tone and color of the garnet; acicular crystals 

 penetrating limpid quartz when cut affords the Venus hair stone., Jfeche 

 cPamour^ or love's arrows. Rutile occurs in granite, gneiss, mica, slate,, 

 and syenitic rocks, occasionally in granular limestones. 



One hundred parts contain: Titanium, 60.98; oxygen, ol».t>2. 



SAMARSKITE. 



This mineral is occasionally cut as a collector's gem. Its color is 

 velvety black; luster, siibmetallic and shining; hardness, 5.5; specific 

 gravity, 5.68; color, opaque. 



SCAPOLITE. 



AV ERX EK ITE W I LSOX ITE. 



Scapolite occurs in tetragonal crystals and massive; luster, vitreous 

 to pearly, occasionally resinous; color, white, gray, blue, green, and 

 red, usually of faint shades; hardness, nearly 6; specific gravit}', 2.7. 



