VARIETIES OE GRANITE. 
557 
merits were thoroughly mixed up together, and then crystal¬ 
lized under precisely similar conditions. There are, how¬ 
ever, many accidental, or “ occasional,” minei'als, as they are 
termed, which belong to granite. Among these black schorl 
or tourmaline, actinolite, zircon, garnet, and fluor spar are not 
uncommon ; but they are too sparingly dispersed to modify 
the general aspect of the rock. They show, nevertheless, 
that the ingredients were not everywhere exactly the same; 
and a still greater difference may be traced in the ever-vary¬ 
ing proportions of the feldspar, quartz, and mica. 
Talcose Granite^ or Protogine of the French, is a mixture 
of feldspar, quartz, and talc. It abounds in the Alps, and in 
some parts of Cornwall, producing by its decomposition the 
kaolin or china clay, more than 12,000 tons of which are an¬ 
nually exported from that country for the potteries. 
Schorl-rock^ and Schorly Granite. —The former of these is 
an aggregate of schorl, or tourmaline, and quartz. When 
feldspar and mica are also present, it may be called schorly 
granite. This kind of granite is comparatively rare. 
Eurite^Feldstone. —Eurite is a rock in which the ingredients 
of granite are blended into a finely granular mass, mica be¬ 
ing usually absent, and, when present, in such minute flakes 
as to be invisible to the naked* eye. It is sometimes called 
Feldstone^ and when the crystals of feldspar are conspicuous 
it becomes Feldspar porphyry. All these and other varieties 
of granite pass into certain kinds of trap—a circumstance 
which affords one of many arguments in favor of what is 
now the prevailing opinion, that the granites are also of 
igneous origin. The contrast of the most crystalline form 
of granite to that of the most common and earthy trap is 
undoubtedly great; but each member of the volcanic class 
is capable of becoming porphyritic, and the base of the por¬ 
phyry may be more and more crystalline, until the mass 
passes to the kind of granite most nearly allied in mineral 
composition. 
Syenitic Granite. —The quadruple compound of quartz, 
feldspar, mica, and hornblende, may be so termed, and form 
a passage between the granites and the syenites. This rock 
occurs in Scotland and in Guernsey. 
Syenite. —We now come to the second division of the plu- 
tonic rocks, or those having less than 60 per cent, of silica, 
and which, as before stated (p. 552), are usually called syenit¬ 
ic. Syenite originally received its name from the celebrated 
ancient quarries of Syene, in Egypt. It differs from granite 
in having hornblende as a substitute for mica, and being with¬ 
out quartz. Werner at least considered syenite as a binary 
