172 FIRST YEAR COURSE IN GENERAL SCIENCE 



Connecticut from which the crushed mineral is shipped to 

 various potteries in New York and New Jersey. 



194. Mica. Mica has a composition similar to feldspar, 

 but it has different properties. It is' usually gray or very 

 dark in color, and breaks into thin sheets, which are almost 

 transparent and are very tough. It does not decompose 

 as readily as feldspar. The shining scales found in 

 sand and sandstone are mica. Sheets of mica, commonly 

 called isinglass, are used in the doors of stoves, because 

 mica is not affected by the heat and the fire can be seen 

 through it. 



195. Hornblende. Hornblende is another mineral simi- 

 lar to feldspar in composition. Very small pieces of horn- 

 blende often look like mica. Unlike mica, however, it is 

 brittle and does not split into thin layers. It has various 

 colors and forms. One kind, called asbestos, is fibrous; its 

 threads are made into a kind of paper or cloth. Asbestos is 

 used to protect surfaces from heat, because it is non-com- 

 bustible and infusible and is also a non-conductor of heat. 

 It is often used for a covering to furnace and steam pipes, 

 to prevent the radiation of heat from the pipes. 



Quartz, feldspar, and either mica or hornblende are the 

 minerals which compose the great class of rocks known as 

 granite. 



196. Calcite. Calcite, or carbonate of lime, is the name 

 of a mineral composed of calcium, carbon, and oxygen. It is 

 sometimes found in the fornTof clear, transparent crystals, 

 but more often it occurs in an opaque, non-crystalline form 

 called limestone. Limestone is white or gray, and is much 

 softer than quartz. On being heated, it gives off carbon 

 dioxide and leaves lime. 



Limestone is soluble in water in which carbon dioxide has 

 been dissolved. Rain water that has passed through the 

 soil contains dissolved carbon dioxide obtained from the air 

 and the decay of plants. As this water flows over and 



