830 Handbook of Nature-Study 



fissures or cracks in the rock, thus forming bodies called "veins." Other 

 materials are often deposited at the same time, and in this way the ores of 

 the precious metals came to be associated with quartz. Sometimes quartz 

 is deposited from hot springs or geysers, forming a spongy substance called 

 sinter. In this case, some of the water is combined with the quartz, making 

 what is called opal. Quartz crystal will cut glass. 



Quartz occurs in many varieties : (a) In crystals like glass. If colorless 

 and transparent it is called rock crystal ; if smoky brown, it is called 

 smoky quartz; if purple, amethyst, (b) In crystals, glassy but not 

 transparent. If white, it is milky quartz; if pink, rose quartz, (c) As a 

 compact crystalline structure without luster, waxy or dull, opaque or 

 translucent, when polished. If bright red, it is carnelian ; if brownish red, 

 sard; if in various colors in bands, agate; if in horizontal layers, onyx; if 

 dull red or brown, jasper; if green with red spots, bloodstone; if smoky or 

 gray, breaking with small, shell-like or conchoidal fractures, flint. 



Rock crystals are used in jewelry and especially are made to imitate 

 diamonds. The amethyst is much prized as a semi-precious stone. Car- 

 nelian, bloodstone and agate are also used in jewelry; agate is used also in 

 making many ornamental objects, and to make little mortars and pestles 

 for grinding hard substances. 



One of the marvels of the world is the petrified forest of Arizona, now set 

 aside by the government as a national reserve. Great trees have been 

 changed to agate and flint, the silica being substituted for the tissues of the 

 wood so that the texture is preserved though the material is changed. 



When our country was first settled, flint was used to start fires by strik- 

 ing it with steel and letting the sparks fly into dry, fine material, called 

 tinder. It was also used in guns before the invention of cartridges, and the 

 guns were called flintlocks. The Indians used flint to make hatchets and 

 for tips to their arrows. The making of flint implements dates far back 

 into prehistoric times; it was probably one of the flrst steps upward which 

 man achieved in his long, hard climb from a level with the brute creation 

 to the heights attained by our present civilization. 



Quartz sand is used in making glass. It is melted with soda or potash or 

 lead, and the glass varies in hardness according to the minerals added. 

 Quartz is also used for sandpaper and glass paper; and ground to a fine 

 powder, it is combined with Japans and oils and used as a finish for wood 

 surfaces. Mineral wool is made from the slag refuse of furnaces where glass 

 is made, and is used for rat-proof and fireproof padding for the walls of 

 houses. Quartz combined with sodium or potassium and water, forms a 

 liquid called water-glass, which is used for waterproof surfaces; it is also 

 fireproof to a certain degree. Water-glass is the best substance in which to 

 preserve eggs ; one part of commercial water-glass to ten parts of water 

 makes a proper solution for this purpose. 



LESSON CCXIV 



Quartz 



Leading thought — Quartz is one of the most common of minerals. It 

 occurs in many forms. As a crystal it is six-sided, and the ends terminate 

 in a six-sided pyramid. It is very hard and will scratch and cut glass. 

 When broken, it has a glassy luster and it does not break smoothly but 

 rihows an uneven surface. 



