THE GRANITE INDUSTRY.

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The Term "Granite" as Used in This Report.

The term "granite," as it is used in this report, might more properly, from the strictly scientific standpoint, be replaced by the designation "crystalline siliceous rocks." Since, however, the report is of interest chiefly as a statistical production, and is intended to give to those interested in the commercial aspects of the subject information bearing upon not only the true granites, but also upon those rocks whose general properties and industrial applications are the same as those of true granites, it has been thought wiser to use the term "granite" as it is understood by quarrymen. Most of the material included under this head is really true granite, but some of it is granite only in the commercial sense of the term. The tables giving the values of granite output in the various States of the country show, therefore, no distinction between true granites, syenites, trap rocks, gneisses, and crystalline schists.

Components of Granite.

The essential components of the true granites are quartz and feldspar. Quite a number of other minerals are, however, to be found in the granites, and these have been classified by Mr. G. P. Merrill, in the Tenth Census report on stone, as follows:

Value of Different Types of Stone in Various States

 

The following statements relative to the minerals to be found in granites is a condensed abstract of matter contained in the Tenth Census report on stone, referred to above:

Of the two essential minerals, quartz and feldspar, the former is invariable in composition; but in the form of the particles and in appearance it is quite variable. As is evident from the enumeration of the various kinds of feldspar already given, there is much latitude for differences in granites, due to the feldspathic constituent. According to the kinds of feldspar present, the granite shows a number of variations in color, which may be due to the color of the feldspar itself or to its transparent or semitransparent character, and its consequent effect upon light. Red and pink granites owe their color to the feldspars contained in them; dark effects in granite are sometimes caused by the absorption of light effected by transparent crystals of feldspar. While the hardness of quartz is always much the same, that of the feldspars is subject to considerable variation in its resistance to the stonecutter.s tools.

The variation in the amounts and the kinds of accessory ingredients is great, and these determine very largely the character of the stone and its susceptibility to ornamentation or polish. Of these accessories mica is the most common. White muscovite gives a light effect to the stone, but if it appears in the form of black biotite the granite is dark in general tone. Much interest attaches to mica as a granitic constituent, for, while its color effects may be very attractive, it does not polish so well as the other constituents, nor does it retain polish so well as the other constituents, frequently becoming dull on exposure. In stone for polishing the manner of occurrence of the mica particles is of importance as well as their amount. Numerous fine particles are less objectionable, if scattered promiscuously, than are occasionally occurring larger crystals.

Mica is frequently replaced wholly or in part by the minerals hornblende and pyroxene. Both minerals are frequently present in the same rock. Hornblende is more desirable than mica as a constituent of granite, having cleavage in two planes instead of one, as in mica, and polishing much more easily. Pyroxene is more brittle than hornblende, and is therefore liable to break out in polishing, leaving little pits which mar the surface. The presence of pyroxene in granite is sometimes a source of much vexation to the quarryman and stonecutter. Of the three minerals, mica, hornblende, and pyroxene, the second is, all things considered, the most desirable as a constituent of granite.

Classification of United States Granites.

According to the Tenth Census report on stone, the granites quarried throughout the United States may be classed as follows:

Muscovite granite, biotite granite, muscovite-biotite granite, hornblende granite, hornblende-biotite granite, granitel (or granite without any accessory). Lines of distinction between these varieties are by no means sharply drawn, one kind gradually merging into another in many cases.

Muscovite granite.-This variety is always light in color, from the nearly colorless character of the muscovite. Comparatively little is quarried in the United States. A highly important example is that produced at Barre, Vt.

Muscovite-Biotite granite.-As the name implies, this granite stands between the two already considered. The essential constituents are quartz, orthoclase, muscovite, and biotite. The Concord, N. H., granite is a good example of this variety; similar to it is the stone from quarries at Allenstown, Sunapee, and Ramney.

Hornblende granite.-In addition to the hornblende contained in this granite as the characterizing accessory, black mica is in nearly all cases likewise found. Biotite is found as a microscopic constituent in many hornblende granites, and the name "hornblende granite" is, therefore, restricted to those in which no biotite is visible to the naked eye. Granite belonging to this class is quarried at Peabody, Mass., and also at Mount Desert, Me.

Hornblende-biotite granite.-Some of the most beautiful of our granites belong to this class, notably so-called black granite from St. George, Me., and some of that quarried at Cape Ann, Massachusetts, and at Sauk Rapids, Minn. The essential constituents are quartz, orthoclase, hornblende, and biotite. These granites are susceptible of fine and lasting polish.

Epidote granite.-The granites of this class in the United States are rare, an example being that quarried at Dedham, Mass. The rock works easily and takes a good polish.

Syenite.-The absence of quartz in a granite, or its presence only to the extent of forming an accessory constituent, determines its classification as a syenite. Fine syenites are known to occur, but they have not been extensively quarried.

Gneiss.-Stratification determines the classification of granite as gneiss. Its cleavage enables it to be quarried in the form of slabs suitable for curbing and similar uses in which slabs are desirable. The stratification is largely determined by the uniformity in the direction of the flat cleavage planes of the mica present in it. The terms "bastard granite" and "stratified granite" are commonly used in reference to gneiss. The only essential difference between granite and gneiss being in the matter of stratification in the latter, there is good reason for the use of the single term "granite" as applied to gneiss.

Mica schist.-The minerals present in this rock are essentially quartz and mica. It differs from gneiss in its lack of feldspar. This variety is easily quarried, and is well adapted to foundation construction and bridge work, but it is not in general favor for fine superstructures.

Diabase.-This term includes rocks commonly called trap rock and black granite. The essential minerals are augite and triclinic feldspar. Microscopic accessories are magnetite, titanic iron, and frequently apatite and black mica. These rocks are eruptive and occur in dikes. Examples of this variety are the products of quarries at Weehawken, N. J., and other localities in the same State, and in Pennsylvania and Virginia.

Basalt.-This rock differs from diabase in being of finer texture and of more recent origin. In California this rock is extensively employed in the manufacture of paving blocks.

Porphyry.-In this rock the constituent minerals, essentially quartz and orthoclase feldspar, are exceedingly minute, making the rock compact and close-grained. They are of eruptive origin and occur in dikes, like trap rocks. They show considerable variation in color, are almost indestructible, and take a fine polish. They are cut with difficulty and their hardness and lack of stratification constitute serious obstacles in quarrying. In this connection the reader is reminded of the interesting rediscovery of the ancient Egyptian quarries of porphyry described in the Report on Mineral Resources for 1893. Steps have been taken toward the reworking of these long-abandoned quarries by Messrs. Farmer and Bridley, of London. Quartz-porphyry is found at Fairfield, Pa., and at Stone Mountain, Missouri.

Geographical Distribution of the Various Classes of Granite.

The following list, from the writer.s report on granite for the Eleventh Census, gives a general idea of the geographical distribution of granite, and indicates most of the particular kinds that have been or are now being quarried in the various localities mentioned:

The following list gives the same data as contained in the preceding one, except that the arrangement is by kinds of granite instead of by States:

Hornblende-biotite granite.-Pulaski County, Ark.; Placer and Sacramento counties, Cal.; Penobscot and Knox counties, Me.; Essex County, Mass.; Iron and St. Francois counties, Mo.; Carroll County, N. H.; Mecklenburg County, N. C.; Fairfield County, S. C.; Salt Lake and Weber Counties, Utah.

Elæsyenite-Garland County, Ark.

Quartz diorite-Placer County, Cal.

Basalt-Solano, Sonoma, and Alameda counties, Cal.; Jefferson County, Colo.; Clackamas and Columbia counties, Oreg.

Biotite granite-Placer County, Cal.; Clear Creek and Jefferson counties, Colo.; Litchfield, New Haven, New London and Fairfield counties, Conn.; Knox, York, Washington, Lincoln, Waldo, Oxford, Kennebec, and Hancock counties, Me.; Baltimore, Howard, and Montgomery counties, Md.; Norfolk, Middlesex, Bristol, Worcester, and Plymouth counties, Mass.; Cheshire, Hillsboro, Grafton, and Rockingham counties, N. H.; Putnam County, N. Y.; Warren, Franklin, Gaston, Granville, Almance, Davidson, Mecklenburg, Iredell, Forsyth, Guilford, Richmond, and Anson counties, N. C.; Washington, Kent, and Providence counties, R. I.; Fairfield, Charleston, Aiken, Lexington, Richland, Edgefield, and Newberry counties, S. C.; Burnet County, Tex.; Washington and Essex counties, Vt.; Dinwiddie, Chesterfield, and Henrico counties, Va.

Andesite-Shasta County, Cal.; Multnomah County, Oreg.

Andesitic tufa-Solano County, Cal.

Quartz porphyry-San Bernardino County, Cal.; Lake and St. Louis counties, Minn.; Green Lake County, Wis.

Basaltic tufa-Tehama County, Cal.

Diorite-Chaffee County, Colo.; Berks County, Pa.; El Paso County, Tex.

Rhyolite-Chaffee and Conejos counties, Colo.

Rhyolitic tufa-Douglas County, Colo.

Muscovite-biotite gneiss-Litchfield County, Conn.; Kennebec, Waldo, and Franklin counties, Me.

Biotite gneiss-Litchfield, New Haven, New London, Windham, Tolland, and Hartford counties, Conn.; Lincoln, Franklin, and Audroscoggin counties, Me.; Cecil and Baltimore counties Md.; Franklin County, Mass.; Passaic County, N. J.; Westchester and Rockland counties, N. Y.; Cleveland, McDowell, Caldwell, Wilson, Stokes, Iredell, Wake, and Guilford counties, N. C.; Philadelphia and Delaware counties, Pa.; Providence County, R. I.; Campbell County, Va.; Jackson County, Wis.

Hornblende-biotite gneiss-Middlesex and Fairfield counties, Conn.; Fulton County, Ga.

Diabase-New Haven County, Conn.; Washington and Knox counties, Me.; Middlesex and Hampden counties, Mass.; St. Louis County, Minn.; Hudson County, N. J.; Linn County, Oreg.; Adams, York, Berks, and Lancaster counties, Pa.; Loudoun and Fauquier counties, Va.

Augite-hornblende gneiss-Newcastle County, Del.

Muscovite granite-Dekalb County, Ga.; Warren County, N. C.; Windsor County, Vt.; Spottsylvania County, Va.

Hornblende granite-Placer County, Cal.; Hancock County, Me.; Norfolk and Essex counties, Mass.; Sherburne, Benton, and Lake counties, Minn.; Morris County, N. J.; Marathon County, Wis.

Olivine diabase-Washington County, Me.; Chisago County, Minn.; Iron County, Mo.

Gabbro-Baltimore County, Md.; St. Louis County, Minn.; Vermont.

Epidote granite-Norfolk County, Mass.

Biotite-muscovite granite-Worcester and Berkshire counties, Mass.; Merrimack, Cheshire, Hillsboro, Grafton, Sullivan, and Strafford counties, N. H.

Biotite-muscovite granite-Rowan County, N. C.; Caledonia County, Vt.

Muscovite gneiss-Clear Creek County, Colo.; Middlesex, Essex, Worcester, and Hampden counties, Mass.; Philadelphia and Berks counties, Pa.

Melaphyre-Sulfolk County, Mass.

Hornblende-mica granite-Benton County, Minn.; Lewis and Clarke County, Mont.; Jefferson County, N. Y.

Granite-Iron County, Mo.; Rowan and Orange counties, N. C.; Jackson and Columbia counties, Oregon; Washington County, R. I.; Minnehaha County, S. Dak.; Stevens County, Wash.; Marquette County, Wis.

Hornblende andesite-Washoe County, Nev.

Biotite-epidote gneiss-Grafton County, N. Y.

Norite-Essex County, N. Y.

Hornblende gneiss-Burke County, N. C.; Philadelphia County, Pa.; Providence County, R. I.

Biotite-muscovite gneiss-Delaware County, Pa.

Biotite schist-Fauquier County, Va.

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