A strange thing is that big crystals are always made up of little crystals. So what looks like one crystal is really a United States of crystals, all like each other and each like all of them put together, much as our federal government repeats the form of the State governments, and the State governments duplicate the government at Washington on a smaller scale.
THE SAND GRAINS AND THE CRYSTAL FAIRIES
The crystal fairies often give battered sand grains a new lease of life and these pictures show how they do it. Fig. "a" is a single sand grain which has grown into crystal form; "b" shows parallel growths about a grain; "c" is a group of neighboring grains that have crowded each other so in their growth that the crystal facets have been destroyed. Sounds odd to speak of sand grains "growing," doesn't it? But they do!
But why do the little crystals always come together in just such a way as to make big crystals shaped exactly like themselves?
Goodness knows!
But whatever the how and the why of it may be, not only do the crystal people stick as closely to the family pattern in dress as the Scotch Highlanders do to the plaids of their clans, but the crystals are clannish in another way. When a clay rock, for example, is dissolved by the heat, moisture, and chemicals down in the land of change, the particles of the same kind that are scattered through it hunt each other out, and ever after cling together, like Emmy Lou and her "nintimate friends." You've noticed how "spotty" granite is, haven't you? This is because it is made up of different kinds of minerals; but, although the crystals in all follow the granite pattern, the particles of each kind of mineral "flock together." The feldspars and the micas never mix.
JUST TRY IT WITH A PIECE OF PAPER
Now take a piece of writing paper and roll it into a tube and I'll show you something else. Stand the roll up between your two hands and press down on the top. It takes a good deal of pressure to bend or break it, doesn't it? Now lay it on its side and squeeze. It breaks right away.
But how should the crystals in a piece of granite know that a column of anything will stand so much more weight when the pressure comes on the ends than when it comes on the sides? They seem to know; for I'll tell you what they do, away down there in the dark of the earth. The crystals stand at right angles to the pressure on the rock in which they are forming. Sometimes, because of the movements of the earth as it shrinks and cracks, the crystals already formed in granite are crushed over on their sides. Then, in course of time, they form again, but this time they stand upright, with their "heads and shoulders" against the burden—little Atlases supporting the world! And they not only manage to get up and stand up straight when re-formed under pressure, but they stand closer together than they did before; they close up ranks, like soldiers with serious business before them.