134 SILICA. 



tallos, meaning ice. The pure specimens are often cut and 

 used in jewelry, under the name of " white stone." 



It is often used for optical instruments and spectacle glass, 

 and even in ancient times was made into cups and vases. 

 Nero is said to have dashed to pieces two cups of this kind 

 on hearing of the revolt that caused his ruin, one of which 

 cost him a sum equal to $3000. 



Amethyst. A purple or bluish-violet variety of quartz- 

 crystal, often of great beauty. The color is owing to a 

 trace of oxyd of manganese. It was so called on account 

 of its supposed preservative powers against intoxication. 

 The amethyst, especially when large and finely colored, 

 is highly esteemed as a gem. It is always set in gold. 



Rose Quartz. A pink or rose-colored quartz. It seldom 

 occurs in crystals, but generally in masses much fractured, 

 and imperfectly transparent. The color fades on exposure 

 to the light, and on this account it is little used as an orna- 

 mental stone, yet is sometimes cut into cups and vases. 

 The color may be restored by leaving it in a moist place. 



False Topaz. This name is applied to the light yellow 

 pellucid crystals. They are often cut and set for topazes. 

 The absence of cleavage distinguishes it from true topaz. 

 The name citrine, often applied to this variety, alludes to its 

 yellow color. 



Smoky Quartz. A smoky-tinted quartz crystal. The 

 color is sometimes so dark as to be nearly black and opaque 

 except in splinters. Crystals of the lighter shades are often 

 extremely beautiful and are used for seals and the less deli- 

 cate kinds of jewelry. It is the cairngorum stone. 



Milky quartz. A milk-whi + e, nearly opaque, massive 

 quartz, of very common occurrence. It has often a greasy 

 luster, and is then called greasy quartz. 



Prase. A leek-green massive quartz, resembling some 

 shades of beryl in tint, but easily distinguished by the ab- 

 sence of cleavage and its infusibility. It is supposed to be 

 colored by a trace of iron. 



Avtnturine Quartz. Common quartz spangled throughout 

 with scales of golden-yellow mica. It is usually translucent, 

 and gray, brown, or reddish brown, in color. The artificial 



What use is made of rock crystal ? "What is the color of amethyst ? 

 T^hy was it so called? What is rose quartz? What is said of its 

 •olor ? What is false topaz ? How is it used ? What is smoky quartz ? 

 JVhat is milky quartz ? What is prase ? What is aventurine quartz * 



