It is important that an architect should have some knowledge of the nature of the different kinds of stone, that he may know what stone is best to use under any given circumstances, and what stones not to use. It can hardly be expected that an architect shall be a geologist, a mineralogist or a chemist, and thus capable of determining the exact composition of a stone, but it is expected of him that he shall know enough of the subject to specify stones that shall have sufficient strength and durability and that will not become discolored through chemical changes in their constituents.
To acquire such a knowledge of building stones requires not only a study of their mineral constituents and of their structure, but also accurate observation and much experience with stones.
The following short description of the principal building stones of this country, with the localities in which they are quarried, will enable the young architect to get some idea of their composition and characteristics, and, it is hoped, assist him in making a judicious selection of stones for special cases.* The stones are classed according to their structure and composition.
The granites are massive rocks occurring most frequently as the central portions of mountain chains. They are a hard, granular stone, composed principally of quartz, feldspar and mica, in varying proportions. When the stone contains a large proportion of quartz it is very hard and difficult to work. When there is a considerable proportion of feldspar the stone works more easily.
The color of the granite is principally determined by the color of the feldspar, but the stone may also be light or dark, according as it contains light or dark mica. The usual color of granite is either a light or dark gray, although all shades from light pink to red are found in different localities.
* For a complete work on the subject the reader is referred to "Stones for Building and Decoration," by George P. Merril, Ph.D.; John Wiley & Sons, publishers. Much valuable information relating to building stones may also be found in the various numbers of Stone.
The light fine-grained stones are the strongest and most durable, although almost every granite has sufficient strength for ordinary building construction. It generally breaks with regularity and may be readily quarried, but it is extremely hard and tough and works with great difficulty, so that it is a very expensive stone to use for cut work. It is impossible to do fine carving in most granites. Granite is one of the best stones for foundations, base courses, water tables, etc., and for columns and all places where great strength is required; also for steps, thresholds and for flagging, when it can be slit readily.
Excellent varieties of granite may be obtained in any of the New England States and in most of the Southern States and the Rocky Mountain region, and in California and Minnesota.
As a rule granite can be quarried in any size desired. New quarries should be analyzed to see if they contain iron, in which case it would be dangerous to use the stone for ornamental purposes until its weathering qualities have been thoroughly tested by exposing blocks for a long time to the weather. If the iron is a sulphurate it is quite sure to stain the stone.
Gneiss (pronounced like nice) has the same composition as granite, but the ingredients are arranged in more or less parallel layers. On this account the rock split in such a way as to give parallel flat surfaces, which renders the stone valuable for foundation walls, street paving and flagging. Gneiss is generally taken for granite, and is frequently called by quarrymen stratified or bastard granite.
Syenite is a rock also resembling granite, but containing no quartz. It is a hard, durable stone, generally of fine grain and light gray color. The principal syenite quarries in this country are near Little Rock, Arkansas.*
All three of these stones are badly affected by fire, large pieces breaking off and the stone cracking badly.
Fox Island, Me.; Groton, Conn.; Woodstock, Md.; St. Cloud, Minn., and Nova Scotia granites are spoiled at 9000 F. Hallowell, Me.; Red Beach, Me.; Oak Hill, Me., and Quincy, Mass., granites are spoiled at 1,000° F. The granites standing the highest fire tests are: Barre, Vt.; Concord, N. H.; Ryegate, Vt.; Mt. Desert, Me.
* In many books and papers treating on granite, syenite is described as a rock consisting of quartz, feldspar and hornblende, the latter taking the place of the mica in the true granites. According to the modern methods of classification such rocks are called "hornblende granite."
"The name 'syenite' takes its origin from Syene, Egypt, but the stone from which it was named has been found to contain more mica than hornblende. According to recent lithologists the Syene rock is a hornblende, mica granite, while true syenite, as above stated, is a quartzless Tock." - Merrill.
152. Description of some of the best known Granites.
Vinalhaven, Fox Island, Me. - These quarries are the most extensive in the country; texture of stone rather coarse; color, gray; contains a small amount of hornblende. It takes a good and lasting polish, and is well adapted for all manner of ornamental work and general building purposes. The stone has been used extensively all over the country for both building and monumental purposes.
Hallowell, Me. - This stone is celebrated for its beauty and fine working qualities, and is in great demand for monuments and statuary. It is a fine light gray rock, comparatively pure, the principal constituents being quartz, feldspar and mica. Has been used extensively all over the country.
There are many other quarries of fine granite in Maine.
Quincy, Mass. - The Quincy granite quarries are amongst the oldest in the country. The product is, as a rule, dark blue-gray in color, coarse grained and hard. Composition: quartz, hornblende and feldspar. The polished stairways and pilasters in the new City Hall at Philadelphia are of this stone.
Concord, N. H. - A fine-grained granite, light gray color, with a silver lustre; well-developed rift and grain, and remarkable for the ease with which it can be worked. Constituents: opaque quartz, soda feldspar and white mica. Well adapted for statuary and monumental purposes, as well as for general building. The stone is eminently durable, the New Hampshire State House, built of this stone in 1816-19, being still in an excellent state of preservation. The Congressional Library building, Washington, D. C, is built of this stone.
North Conwdy, N. H. - A coarse-grained granite; colors, red and green, the red being the principal variety. Contains both hornblende and pyroxene. Used in the Union Depot, Portland, Me.
Westerly, R. I. - Granite of fine grain and even texture and of excellent quality. Constituents: quartz, feldspar and mica, with some hornblende. Color, rich light gray or pink, with a distinct tint of brown when polished.
Jonesborough, Me. - At this place is quarried a pink or reddish granite, which is generally considered as the best American red granite at present quarried. The stone is very compact and hard, and much finer in texture than the celebrated red Scotch granite.
St. Cloud, Minn. - Both gray and red granites are quarried at this place; the latter greatly resembles the Scotch granite in color, grain and polish. The gray granite is about one-third quartz and two-thirds feldspar.
Graniteville, Mo. - Here is quarried a very hard red granite, mottled with gray and black, which takes a handsome polish. The stone has been used in many important buildings in St. Louis, Kansas City and Chicago.
Colorado. - This State also contains great quantities of granite, which, however, have been but little developed. The principal quarry is at Gunnison, which produces a blue-gray granite, which may be seen in the Colorado State House.
Georgia. - Excellent grades of light and dark gray granite are contained in this State, but as yet they are developed only to a small extent.