238 DESCRIPTIONS OF MINERALS. 



done by comparing the color of the mark left on it with 

 that of an alloy of known character. The effect of acida 

 upon the mark is a] so noted. 



Besides the above there are other varieties arising from 

 structure. 



Tabular Quartz. Consists of thin plates, either parallel 

 or crossing one another and leaving large open cells. 



Granular Quartz, A rock consisting of quartz grains 

 compactly cemented. The colors are white, gray, flesh-red, 

 yellowish or reddish-brown. It is a hard siliceous sand- 

 stone. Ordinary sandstone often consists of nearly pure 

 quartz. 



Pseudomorphous Quartz. Quartz under the forms of cal- 

 cite, barite, fiuorite or other mineral. Shells, corals, etc., 

 are sometimes found converted into quartz by the ordinary 

 process of petrifaction. 



Silicified Wood. Petrified wood often consists of quartz, 

 quartz having taken the place of the original wood. Some 

 specimens are petrified with chalcedony or agate. 



Penetrating substances. Quartz crystals are sometimes 

 penetrated by other minerals. Eutile, asbestus, actinolite, 

 topaz, tourmaline, chlorite and epidote, are some of these 

 substances. The rutile often looks like needles or fine 

 hairs of a brown color passing through in every direc- 

 tion. They are cut for jewelry, and in France pass by the 

 name of Fleches d'amour (love's arrows). The crystals of 

 Herkimer County, N. Y., often contain a kind of black coal. 

 Other crystals contain cavities filled with some fluid, as 

 water, naphtha, or liquid carbonic acid, or with minute 

 crystals. 



Obs. Quartz is an essential constituent of granite, gneiss, 

 mica schist, and many other common rocks, and the chief 

 or only constituent of many sandstones, and of the sands 

 of most sea-shores. Fine quartz crystals occur in Herki- 

 mer County, New York, at Middlefield, Little Falls, Salis- 

 bury and Newport, in the soil and in cavities in a sand- 

 stone. The beds of iron ore at Fowler and Hermon, St. 

 Lawrence County, afford dodecahedral crystals. Diamond 

 Island, Lake George, Pelham and Chesterfield, Mass., Paris 

 and Perry, Me., Meadow Mt., Md., and Hot Springs, Ar- 

 kansas, are other localities. Pose quartz is found at Albany 

 and Paris, Me. , Acworth, X. H., and Southbury, Conn. ; 

 smoky quartz at Goshen, Mass. ; Paris, Me. ; in North Caro- 



