18 CATALOGUE OF THE COLLECTION OF THE MAYNARD CHAPTER. 



Catalogue of Minerals. 



QUAKTZ. Pure silica; an oxide of silicon, composed of about 47 parts of 

 si icon and 53 of oxygen. The element silicon nev^r occurs in a natural condition 

 uncombined with oxygen. When separated artificially it gppcais in t^o condi- 

 tions ; amorphous (without form) as a black powder, and crystalline as brilliant, 

 black scales. Oxygen, the most abundant element in nature, also noted for the 

 readiness with which it ( ombines with nearly all other elements, when pure, in a 

 natural condition is a gas. Quartz is an exceedingly abundant mineral, perfect- 

 ly transparent when pure, crystallizing in six sided pris-ms. It is fcaid tnough to 

 scratch glass readily and bieaks with a cuived cr thill-lite (clcncl oidai) fract- 

 ure, and it is difficult to make it break with a true cleavage. It feels rather gret.- 

 sy to the touch. 



FIG. 37. 



Quartz Crystals. 



Quartz combines quite readily chemically with other minerals or elements, and 

 often crystallizes thus combined; with iron, producing milky or smoky quartz; with 

 titanic acid, rose quartz; with manganese, amethystine quartz, or amethyst. 



.Mechanically quartz is broken into fragments by ice and frost action; these 

 fragments are worn by water first into pebbles, then into sand, which, under cer- 

 tain conditions, becomes cemented together to form sandstone, which under other 

 conditions may disintegrate back again into sand. 



Organically, quartz which has been taken into solution by water is absor- 

 bed l>y plants, pla.it a limals, and animals, notable ex implt s of which are the dia- 

 tomes, radiolaria, and sponges. The remains of these fjrm flint, which through 

 age becomes novaculite, chert, and hornstone. From ] ls,nt life it is returned to 

 the soil and under favorable conditions becoming agate, r,nd chalcedony. 



Underpressure, forming rock masses through cio~/led crystallization, or in 

 co.n bination with one or all of the following miners If, feldspar, hornblende, mica 

 forming different kinds of granitic rocks, which through age, pressure, and possi- 

 bly partial fusion, become the diabases. 



