GRANITE AND ITS VARIETIES. 
553 
Feldspar, quartz, and mica are usually considered as the 
minerals essential to granite, the feldspar being most abun¬ 
dant in quantity, and the proportion of quartz exceeding that 
of mica. These minerals are united in what is termed a con¬ 
fused crystallization; that is to say, there is no^ regular ar¬ 
rangement of the crystals in granite, as in gneiss (see Fig. 
322, p. 577), except in the variety termed graphic granite, 
which occurs mostly in granitic veins. This variety is a 
compound of feldspar and quartz, so arranged as to produce 
Fig. 606. 
Granite having a cuboidal and rude columnar structure, Land’s End, Cornwall. 
an imperfect laminar structure. The crystals of feldspar 
appear to have been first formed, leaving between them the 
space now occupied by the darker-colored quartz. This 
mineral, when a section is made at right angles to the alter¬ 
nate plates of feldspar and quartz, presents broken lines, 
which have been compared to Hebrew characters. (See Fig. 
608.) The variety of granite called by the French Pegma¬ 
tite^ which is a mixture of quartz and common feldspar, usu¬ 
ally with some small admixture of white silvery mica, often 
passes into graphic granite. 
Ordinary granite, as well as syenite and eurite, usually 
contains two kinds of feldspar: 1st, the common, or ortho- 
clase, in which potash is the prevailing alkali, and this gener- 
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