PHYSICAL PROPERTIES OF GRANITE. 21 
usually have crystallized in the following order : Magnetite, pyrite, 
apatite, zircon, titanite, hornblende, biotite, muscovite, the feld- 
spars, and, last of all, the quartz. It should be noted, however, that 
many of the feldspar crystals contain intergrown quartz, so that 
some of the quartz must therefore have crystallized at the same time 
as the feldspar. The structure of the potash feldspar in some 
granites is very intricate, as it contains microscopic intergrowths of 
a lime-soda feldspar, both having evidently crystallized at the same 
time or in close alternation. Also, as stated above, the potash feld- 
spar may be rimmed with soda-lime feldspar, or vice versa. 
PHYSICAL PROPERTIES. 
Granite derives its physical properties from its mineralogical con- 
stitution, j^articularly from its large content of feldspar and quartz, 
and from its texture. Among these physical properties the most 
important are weight, cohesiveness, elasticity, flexibility, hardness, 
expansibility, porosity, and vitreousness. Each of these qualities will 
be taken up in the order in which they are here stated. 
Weight. — In order to establish a fixed standard the weight of a 
rock is compared to that of an equal volume of distilled water. The 
weight thus determined is called its specific gravity. The specific 
gravity of granite ranges from 2.593 to 2. 731. The average of these 
extremes is 2.G62, wdiich is equivalent to 2 long tons, or 4,480 pounds, 
to the cubic yard, or about 165 pounds to the cubic foot. Geikie ° 
calls attention to the change in the weight of granite when immersed 
in sea water, as given by Stevenson.^ A red granite having a spe- 
cific gravity of 2.71, or 13.2 cubic feet to the ton in air, will in sea 
water of a specific gravity of 1.028 measure 21.30 cubic feet to the ton. 
Cohesiveness. — The amount of cohesiveness of a rock is ascertained 
by determining its crushing strength — that is, the weight in pounds 
required to crush it or to destroy its cohesion. The ultimate com- 
pressive strength of granite ranges from about 15,000 to 43,973 
pounds per square inch, c but the usual range is from 18,000 to 34,000 
pounds. Herrmann d gives the crushing strength of European gran- 
ites as ranging'from 1,100 to over 3,000 kilograms per square centi- 
meter. 
Elasticity. — Tests made at the United States Arsenal at Water- 
town, Mass., to determine the compressive elasticity of specimens of 
granite from Arkansas, Connecticut, Maine, Minnesota, and New 
a Text-book of Geology, 4th ed., p. 568. 
6 Stevenson, T., Harbours, p. 107. 
c These extremes are from Wisconsin granites. See Buckley, Ernest B., on the building 
and ornamental stones of Wisconsin : Bull. Wisconsin Geol. and Nat. Hist. Survey, No. 4, 
pp. 361, 390. 
d Herrmann, O., Steinbruchindustrie und Steinbruchgeologie, p. 43. 
