OXIDES :i.V.J 



caused at this locality by fine crystals of chlorite being deposited 

 on the crystal at different periods of its growth. More compli- 

 cated crystals are found in North Carolina, showing rare forms. 



Quart/ is quarried in Connecticut, Maryland, New York, Wis- 

 consin, and North Carolina, for various purposes. When finely 

 ground it is used as a filler in paints and scouring soaps. It is 

 used in pottery and glass, and recently it has been fused and blown 

 as glass, iii chemical ware, such as evaporating dishes, flasks, cru- 

 cililes, and ignition tubes, for the determination of carbon; here it 

 has the advantage, due to its low coefficient of expansion, of not 

 being liable to crack when submitted to sudden changes of tem- 

 perature ; even when at a bright red heat it may be plunged into 

 cold water without the least danger of cracking. After fusion it 

 lias lost its crystalline structure and is amorphous silica, but on 

 repeatedly heating and cooling, the molecules will rearrange them- 

 selves and become crystalline, and then the tubes are liable to 

 shatter on passing the inversion temperature of ft- to a-quartz. 



Colored quartz. Owing to small quantities of metallic oxides 

 or organic matter as impurities quartz may appear in various 

 colors. Some of the colored varieties have received special names, 

 as citrine or yellow quartz, which is clear and transparent, in 

 appearance very much like the topaz, and indeed when cut, pol- 

 ished, and mounted in jewelry is sold in the trade as topaz, or false 

 topaz. The best examples of this variety are obtained from Brazil. 

 Smoky quartz is a dark colored variety of crystalline quartz which 

 owes its color to organic matter or carbon compounds. The evenly 

 colored transparent specimens are polished and valued as a semi- 

 precious stone. Disentis and St. Gothard, Switzerland, are noted 

 localities. These crystals generally have the faces x and s well 

 developed. In the United States, it occurs at Pike's Peak, Colo- 

 rado ; in Richmond County, New York ; and very large crystals 

 have been obtained at Paradise River, Nova Scotia. 



Amethyst is a purple or bluish violet quartz which is colored with 

 small amounts of manganese or possibly by organic matter. The 

 color may vary greatly ; in most specimens it is unevenly distributed 

 through the crystal, and is usually concentrated at the apex. Dark, 

 evenly colored crystals are much prized as a semiprecious stone. 

 The best colored specimens are from Siberia, India, Uruguay, and 

 Hraxil. Pale varieties are widely distributed. In the United 

 States amethysts of good color are found in Lincoln and Macon 

 counties, North Carolina; Nelson County, Virginia; Rabun 



