12 
NATURE STUDY. 
most widely distributed and most abundant of all, viz., fhe 
feldspar family. The most common species of this family is 
orthoclase, and it, too, is easily recognized by a few prominent 
characteristics. Break open almost any common boulder in New 
England, and we si all probably find all three of the above 
mentioned minerals mixed in varying proportions, and the indi¬ 
vidual particles ranging from minute to coarse. Those little 
shiny scales varying from black to almost colorless is the mica, 
sometimes erroneously called isinglass. The black variety is 
called biotite and the light colored is muscovite, the same ma¬ 
terial that is found in the modern stove door to give a cheery 
appearance to the otherwise monotonous black. Those small 
grains, that are glassy in appearance, more or less transparent, 
and sometimes of a dark smoky hue, are quartz. If we select 
one of the largest of the other pieces and examine it closely, 
we shall notice that one or more of its surfaces are quite flat, 
not so smooth ar.d polished as the mica, but so much so as to 
make it quite unlike the quartz in that particular. If we take a 
piece of the quartz and try to scratch it with a corner or edge of 
this mineral, and vice versa, we shall find that the quartz is the 
harder. If we persist and break up several pieces we shall 
probably soon find a piece where there are two flat surfaces 
perpendicular to each other or very nearly so. We shall see 
also that these two surfaces glisten and reflect the light more 
completely than do the quartz surfaces, which are quite irregu¬ 
lar. The geologist explains this difference by saying that the 
mineral we are comparing with quartz has distinct cleavage, i. e. 
it splits evenly and smoothly in certain directions, while the 
quartz does not, and the surfaces thus exposed are called 
cleavage planes. Those two clearage planes at right angles 
to each other are characteristic of feldspar, and so we find the 
third substance to be of that family. In color the feldspars vary 
here in New England from a white through gray to a flesh red, 
or salmon color. These three minerals are the principal con¬ 
stituents of the rocks granite and gneiss. 
Sometimes, instead of the shining mica surfaces, we find a 
