24 THE GKANITES OF MAINE. 
containing black mica and hornblende is called a biotite-hornblende 
granite. Granites may also be classified according to both their 
mineral and their chemical composition. These two form the basis 
of the latest classification of igneous rocks, which is too complex to 
be outlined here." 
Economic classification. — For economic purposes granites may be 
classified first as to texture — as even grained, or porphyritic, or as 
coarse, medium, or fine, according to the scale given on page 20. 
Those of extra coarse or extra fine texture can be distinguished by 
the prefix very. This scale gives five grades of texture. Granites 
should also be classified as to general color and shade — as pinkish, 
reddish, lavender, or gray or warm gray (that is. a gray showing the 
presence of a slight reddish, reddish-purplish, or yellowish tinge), 
and as dark, medium, or light. They may he further classified and 
designated by the colors of their most conspicuous minerals, the 
feldspars, quartz, and mica. A stone may thus he called a coarse, 
even-grained, warm-gray granite, with lavender ami white feldspars, 
smoky quartz, and black mica: or another may he called a line, even- 
grained, very light gray granite, with white feldspar, clear quartz, 
and both white and black mica. This scheme of classification will 
suffice for general economic purposes. The outline of a complete 
economic description of granite can be constructed from the tests 
enumerated in Part II, on pages 63 66. 
MAINE GRANITES. 
CLASSIFICATION. 
The granites exposed at the Maine quarries fall naturally into six 
groups : 
1. Biotite granite, consisting of the two feldspars, quartz, and 
black mica. 
2. Muscovite-biotite or hiotite-muscovite granite, with both black 
and white mica, the name of the predominating mica being in each 
case the first. 
3. Hornblende-biotite or biotitt -hornblende granite, with horn- 
blende and black mica, named according to the predominance of one 
or the other of these minerals. 
4. Quartz monzonite, in which the amount of lime-soda feldspar is 
so large as to about equal that of the potash feldspar. The monzon- 
ites quarried in Maine contain biotite or biotite and hornblende. 
5. Hornblende granite, consisting of the feldspars, quartz, and 
hornblende. 
a See Cross, Iddings, Pirrson, Washington, Quantitative Classification of Igneous Rocks 
based on Chemical and Mineral Characters, with a Systematic Nomenclature, Chicago, 
1903 ; also Jour. Geology, vol. 10, 1002, pp. :>:,:> et seq. 
