Mineral Guide > Marbles > Granites

Granites

The granites differ so widely from the marbles in composition, as well as in origin, that it is difficult to treat of both within the limits of this short article. The distinguishing feature of a granite, aside from its hardness, is perhaps its granular structure, hence its name, from a Latin word meaning " a grain." It is a more complex rock than the marbles, being made up not of minerals of a single kind, but of a collection of two or more minerals, among which quartz and feldspar are the more abundant, though there is nearly always present an appreciable quantity of mica or hornblende. The granites further differ from the marbles in that in place of being hardened and changed marine sediments, they result from the slow cooling and crystallization, deep down in the earth, of masses of melted material differing in no essential particular from the lavas which flow out from many volcanoes of today.
One of the interesting things about this granite is that it has a granular structure, only owing to an accident of cooling. Had this original molten lava flowed out on the surface instead of coming to rest and slowly cooling under it may be the weight of millions of tons overlying rock, it might have formed a glass, an obsidian, like that of the obsidian cliffs of the Yellowstone National Park.
However, it did form a granite, and that is enough for us at present. But if, as has been stated, the stone must have crystallized under all this amount of overlying material, how does it happen that it is found today lying so nearly upon the surface? The question is an easy one to answer, at least, easy to one who has a good imagination. Dame Nature, it must be remembered, is as fickle as the worst of her sex. She is constantly making and unmaking the garments in which she is clothed, is building up and tearing down to suit new conditions and environments. The geologist will tell you that a constant readjustment is going on, whatever that may mean, but I think we can understand it better if we imagine that this book represents a section of the earth's crust perhaps ten thousand feet thick and fifty miles long by twenty-five broad. Imagine further that throughout long geologic ages, this section becomes folded, as is the formation of mountains, into a bow shape, and that the molten material which presently becomes granite is pushed up into the hollow beneath. Then as time goes on, heat and cold, rain and the gases in the atmosphere eat away the upper portions and leave the granite core exposed to the surface. This is what has actually taken place, and in more than one instance it may be said, with scarcely poetic exaggeration, that our granite ledges are but the roots of old mountain chains which have been long since eroded and sent seaward.
But we must restrain ourselves, and come down to the cold facts of economics. The large majority of our granite quarries are in the north and east, for the very simple reasons that here erosion has been most active, and here as a consequence the rock is best exposed. The stone being harder than the marble cannot be quarried by steam channeling, nor sawn economically by steam saws, but recourse must be had to blasting, and to the patient prod of plug and feather.
Granite has well been called the noblest of rocks. Of varying colors and textures, from the light gray, such as was used in the New Congressional Library Building in Washington, to dark gray, pink or red, it adapts itself to all forms of architectural expression. Its strength and endurance are far beyond the limits of requirements. Formed by Nature for the foundation of mountains, it is well adapted for the most massive and lasting of human structures. The Ancient Egyptians used it for their obelisks, but among no nation of the earth has it been so extensively and systematically used as among our own.
Accused as we are of shams in art and in architecture, of building only for ourselves and for today, it is nevertheless true that the American cities of the present will show a greater-proportion, of granite buildings, public and private, often richly, if not profusely, ornamented, than will those of any other nationality. The stucco imitations of stone, which everywhere go to form the walls of private dwellings, business blocks, government buildings, and palaces of Berlin, St. Petersburg, Vienna, Paris, and other cities of Europe find no favor in a country so richly endowed as ours, and where individual enterprise, as well as public spirit, are striving toward that which is not merely effective in general plan but satisfactory in detail as well.
From what has been said relative to the mode of origin of both marbles and granites, it must be apparent that such are to be looked for only in regions that have been subjected to great geological disturbances and erosion. So, in the United States we find either stone quite unknown in the immense interior plans, but abundantly developed in the Appalachian and Rocky Mountain regions, and thence westward to the Pacific Coast.