PHYSICAL PROPERTIES OF GRANITE. 23 
rill a has shown that certain Maryland granites absorb from 0.190 to 
0.258 per cent of water after drying 24 hours at 212° F. and then 
being immersed for 24 hours. 
Vitreousness. — The vitreousness of granite is due to that of its con- 
tained quartz. Under extreme changes of temperature, as in a city 
fire, where water is thrown on the stone, granite exfoliates badly. This 
exfoliation or shelling is attributable to the unequal expansion or 
contraction of its outer and its inner portions under sudden changes 
of temperature. It is also probably connected with the vitreousness 
of the quartz and possibly also in a measure with the liquids contained 
in microscopic cavities of the quartz. The unequal expansive ratios 
of the different constituent minerals would result in general disinte- 
gration, not in exfoliation. 
Buckley h subjected 2-inch cubes of five Wisconsin granites to high 
temperature tests and found that they were all dest-oyed at 1,500° F. 
( )ne of them cracked at 1,000° ; two others began to disintegrate at 
1,200°. The most notable change Avas that "when struck with a 
hammer or scratched with a knife they emitted the sound peculiar to 
a burnt brick." Cutting '' applied a fire test to granites from eighteen 
quarries in Maine, Maryland, Massachusetts, Minnesota, New Hamp- 
shire, Vermont, and Virginia, with the result that after saturation 
they all stood a temperature of 500° F. without damage, but showed 
the first appearance of injury at 700°-800° and were rendered worth- 
less at 1)00 °-l ,000°. Twenty-three sandstones subjected to the same 
tests showed the first appearance of injury at 800°-900° and became 
worthless at 950°-l,200°. His general results agree with those of 
experience as to the relative fire endurance of granite and sandstone/ 
The behavior of granite under very high temperature is not attrib- 
utable to any one physical property. The physical properties of 
granite are further discussed in Part II, under the heading " Tests 
of granite " (pp. 63— 06) . 
CLASSIFICATION. 
The varieties of granite are so numerous that for either scientific 
or economic purposes they need to be classified. 
Scientific classification. — For scientific purposes granites may be 
classified according to their less essential mineral constituents — 
mica, hornblende, and augite. Thus a granite containing white mica 
is termed a muscovite granite; one containing black mica, a biotite 
granite; one containing both, a muscovite-biotite granite. A granite 
"Merrill, G. I\, Maryland Geol. Survey, vol. 2, pp. 04, 95. 
"Op. cit, p. 411. 
c Cutting, Hiram A., Sixth Kept. Agric. Vermont, 1880, pp. 47-54; also, Durability 
of building stone : Am. Jour. Sci., ,°»d ser., vol. 21, 1881, p. 410. 
Merrill, G. P., Stones for building and decoration, p. 435. 
