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Excerpts From

The Granites of Maine, Bulletin 313

By T. Nelson Dale

(Continued)

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Text-Book References on Granite and Black Granites.

As the matter contained in the foregoing pages may not fully provide answers to all questions that may arise in the minds of persons interested in tracing the phenomena in granite quarries to their causes, the names of a few reliable general works in English on the subjects considered are here given.

Diller, Joseph S.  Educational series of rock specimens collected and distributed by the United States Geological Survey: Bull. U. S. Geol. Survey No. 150.  1898. 

Granites, pp. 51, 170-180; gabbro, pp. 51, 52, 278-288; diorite, pp. 241-244; diabase, pp. 264-278; basalt, pp. 51, 52, 254-256.

Geikie, Archibald.  Text-book of geology, fourth edition.  London. 1903.

Granite, etc., pp. 89, 90, 203-209, 402-415, 715-809; gabbro, pp. 231, 232, 256; diorite, p. 223; diabase, p. 233; basalt, p. 234.

Harker, Alfred.  Petrography for students:  An introduction to the study of rocks under the microscope, second edition.  1897.

Granites, pp. 27-41; gabbros, pp. 67-81; diorite, pp. 54-66; basalts, pp. 188-200.

Hatch, Frederick H.  An introduction to the study of petrology; the igneous rocks, second edition.  London.  1891.

Kemp, James F.  A handbook of rocks for use without the microscope, third edition.  New York.  1904.

The granites, pp. 33-38; gabbros, pp. 72-74; diorites, pp. 60-62; diabase, pp. 70-72.

Luquer, Lea M.  Minerals in rock sections, revised edition.  New York.  1905.

Merrill, Geo. P.  A treatise on rocks, rock weathering, and soils.  New York.  1897.

Igneous rocks, pp. 58-64; granites, pp. 65-68; diorites, pp. 81, 82; diabases, pp. 87, 88; basalts, pp. 90, 91; weathering, pp. 170-214.  See also the same headings in the revised edition of the same work, which has just appeared.


Part II. - Economic Features.

The practical side of the granite industry will now be considered.  The sections on the tests of granite and granite quarrying are of general application, but the rest of the matter has reference only to Maine granites and quarries.  A list of the more important works on granite quarries and quarrying and other matters of economic character will be found at the end, together with a glossary of both scientific and quarry terms.

Tests of Granite.

The testing of granite is a subject of considerable importance, as may be seen by its literature.[46]  As pointed out by Merrill, there is danger of attaching undue importance to tests of compressive strength alone, the results of which in nearly all cases far exceed the generous margin allowed by architects beyond that required by the weightiest structures.  On the other hand, there is danger of losing sight of several other important qualities which ought to be carefully tested and upon which the economic value of granite in part depends.  The following tests include all the kinds made at European testing institutions or recommended by American authorities, as well as some suggested by the investigation of Maine granites.

Chemical analysis.-Chemical analysis is made in order to determine the amount of iron and lime, or to detect anything abnormal in the composition.

Determination of CaCO3.-Tests are made to determine the presence of lime not combined with silicates in order to ascertain the percentage of CaCO3 (lime carbonate) present.  This is done by powdering and treatment with warm dilute acetic acid.  (See p. 94.)

Test for discoloration.-The method applied by Daly (Bull. U. S. Geol. Survey No. 209, p. 52) seems to be well adapted for this purpose.  A piece of fresh rock is immersed in a stream of carbon-dioxide gas for 20 minutes and then kept in an atmosphere of that gas for 24 hours.  Another piece of fresh rock is placed in an atmosphere of purified oxygen over night and then exposed for 30 minutes to a temperature of 150 C. (302 F).  Any discoloration due to the carbonization or oxidation of the minutest particles of any mineral would sure to show itself under these tests.

Mineral composition.-This is determined by the microscopic examination of a considerable number of typical thin sections.  All the mineral constituents are noted, and the average size of the mineral particles in the case of the fine-textured granites is estimated.  Any peculiarities of texture, rift, etc., can also be noted.

Proportions of minerals.-A method has been devised by Rosiwal, of the Austrian Geological Survey,[47] by which the approximate proportions of the chief minerals (feldspar, quartz, mica, hornblende) and their average size can be determined.  This consists in tracing a network of lines intersecting one another at right angles upon a polished granite surface, at intervals so far distant that no two parallel lines will traverse the same mineral particle.  The total length of the lines is measured, then the diameters of all the particles of each kind of mineral are added separately and their proportion to the total length of the lines obtained.  The average size of the particles of each mineral can be also calculated from the same measurements.  Although this method was primarily designed for application to the coarse and medium granites, it can be extended also to the finer ones by drawing the lines upon camera-lucida drawings made from thin sections of such granites under polarized light.  As the quartz is the source of the vitreousness of the rock the determination of its amount is important.  The incompleteness of the collection of polished specimens of Maine granites and the short limit of time available have alone prevented the application of this method in the preparation for this report, but the method was experimentally applied to a specimen of the coarse reddish granite from Hardwood Island, near Jonesport, and the results are given on page 173.

Polish.-Besides the manifest object of this test it also facilitates exact descriptions of color and comparisons between different granites.  The size of the mica plates determines the brilliancy and durability of the polish more than does their number-that is, a considerable number of very minute mica plates is not objectionable.

Hardness.-As pointed out by Hawes[48] the hardness of certain granites is not due entirely to the quartz, which is always equally hard and brittle and which the tools do not cut but crush, but to the feldspar, which is of variable hardness and, it might be added, has different cleavages, and the proportion of which in relation to quartz also varies.  Rosiwal,[49] adopting a principle established by Toula, takes a piece of smooth unpolished granite of about 2 grams weight and rubs it with emery (of 0.2 mm. diameter of particle) upon a glass or metal plate for 6 or 8 minutes until the emery loses its effectiveness.  The granite is then weighed again and its loss of volume calculated.  He found, assigning to emery an arbitrary value of 1,000 as representing its average hardness, that granite from 9 localities showed the following degrees of hardness:  31.7, 38.1, 41.7, 44.8, 48.4, 50.7, 52.9, 56.6, and 67.1.  The extremes of these figures show that some granites have a general hardness more than twice as great as others.

J. F. Williams[50] proposed to determine the relative hardness of granites by noting the rate of penetration of a drill of a given diameter, or by measuring the distance to which such a drill will penetrate without being sharpened, or the amount of surface of rough-pointed granite which can be reduced to a bush-hammered surface per hour.  Since the introduction of pneumatic drills and surfacers these methods can be easily applied.

Compressive strength.-The methods of testing the strength of building stones have grown in precision.  The first requisite is that the cubes to be tested should be sawed by diamond saws and not hammered out.  The next is that the direction of both rift and grain should be indicated thereon, and that three cubes should be tested, one with pressure applied parallel to the direction of the rift, one applied parallel to that of the grain, and the third at right angles to rift and grain.  Where the rift and grain are pronounced the three results will differ.  As in the reports of tests made with testing machine at the Watertown Arsenal, Mass., the number of pounds pressure at which the first crack is produced should always be given, as well as that at which the cube is crushed.  It is assumed that these tests are made in a dry atmosphere.

Traverse strength, shearing strength, and compressive elasticity.-It has been found useful for certain architectural purposes to test these qualities in granite.[51]

Porosity.-Buckley points out[52] that the danger from frost depends not upon the amount of absorption but upon the size of the pore space.  Rocks with large pore spaces stand frost better than those with small ones, because they do not retain the water that they absorb.  Tests of porosity are therefore important.  Buckley used the dry and saturated weights obtained for the samples used in computing the specific gravity.

The difference in these weights was multiplied by the specific gravity of the rock.  This amount was added to the dry weight, giving the sum.  The difference of the dry and saturated weights multiplied by the specific gravity of the rock was then divided by the sum.  This last result is the actual percentage of pore space compared with the volume of the sample tested.

Freezing and thawing.-Buckley's method[53] consists in drying 1-inch and 2-inch cubes at a temperature of 110 C. and weighing them.  After being saturated in distilled water they were exposed overnight to a temperature below freezing.  They were then thawed out and soaked in warm distilled water.  This process was continued for thirty-five days, when they were again dried at 110 C. and weighed.  Finally the same stones were subjected to the tests for compressive strength and the results compared with those for stones not thus treated.

Absorption and compression.-The complete saturation of a stone and the determination of the amount of absorption are effected by a method described at length by Buckley.[54]  The saturated stone should then be tested for compressive strength and the result compared with that obtained from dry stone.

Behavior under fire.-This test is best applied to saturated specimens, which are then exposed in a laboratory furnace to a temperature up to 1,500F. and the effect noted.  Some of them can be allowed to cool gradually, but others should be immersed quickly in cold water, or they may be exposed to high temperature while under compression and then cooled slowly or quickly.[55]

Specific gravity.-The specific gravity is the weight of the stone at 16 C. compared with that of the same volume of distilled water at 4 C.  All air should first be removed from the piece to be tested by boiling in distilled water.  The specific gravity is also required for the test of porosity.

Weight per cubic foot.-The weight of the dry stone per cubic foot is obtained by multiplying its specific gravity by the weight of a cubic foot of water, but from this there should be deducted "the weight of a quantity of stone of the same specific gravity equal in volume to the percentage of the pore space in the stone."[56]  This gives the actual weight of the stone free from interstitial water.

Coefficient of expansion.-Finally, it may be desirable to obtain the coefficient of expansion of a granite intended for some particular construction.  The expansion of certain granites was determined at the Watertown Arsenal by hot and cold water baths.  The stones thus tested were afterwards subjected to the test for transverse strength, when it was found that they had lost 16.93 per cent of their original strength.[57]

A list of the various tests applied to building stones by German testing institutions is given by Herrmann.[58]

Adaptability to Different Purposes.

The successful use of granite depends upon a careful consideration of its various adaptabilities.  The granites proper, as will be seen by the description of the Maine granites alone (pp. 73, 74), include stones which vary greatly in texture, color, and shade.  The coarse-textured ones are best adapted to massive structures, while the fine-textured ones are better adapted to lighter structures, monuments, and statues.  The reason for this is that in coarse-textured granites the large feldspars crossing the various sculptural designs at all sorts of angles produce lines and reflections that interfere with the lights and shades produced by the sculptor's design, and thus mar their effect.  The fine granites are well adapted to light structures and to fine sculpture, as is shown in the delicately carved panel and the statue represented in Pl. XIV, A and B.  Some coarse granites, however, lend themselves well to coarse carvings, especially when these are to be placed in the higher parts of buildings, as was the lintel of Vinalhaven granite shown in Pl. XIII, A.  Then there is a matter of color and shade.  There is large room for the exercise of artistic taste in deciding which colors and shade will best harmonize or contrast with one another in a granite structure or with the colors of other stones or materials in a composite structure.  There is also room for choice between different granites in ornamental work, because of the different amount of contrast between the polished, hammered, and rough surfaces of stones of different color and texture, although the polished surface is always darkest and the hammered lightest. Tarr[59] in 1895 wrote of a demand by architects for rust-colored granite (sap) for use in connection with light-colored stone in order to produce pleasing contrasts.  (See further p. 72.)

The black granite are obviously best adapted for inscriptions where legibility at a distance is the prime object, and also for all ornamental work in which more marked contrasts are desired than the ordinary granite can furnish.  The black granite are sometimes combined with ordinary granite of light shade in monumental work, the die being of black granite.

Granite Quarrying.

The problems that confront the granite quarryman are numerous.  Their solution requires not only capital, but practical experience, judgment, a little geological knowledge, and some mathematics.  It is, first of all, assumed that suitably prepared specimens of the fresh rock have been procured and subjected by competent persons, provided with the necessary machines and instruments, to the tests enumerated on pages 63-66 in order that the quality of the stone may be scientifically determined.

Exploration of surface.-The next step is a careful exploration of the granite surface, if necessary, by stripping in trenches, with a view to determine the areal extent of the quality of stone tested, the character of the jointing, the presence of headings, dikes, and veins, and the frequency of knots.

Stripping.-The thickness of soil or till upon the granite surface and that of the decomposed surface rock should be estimated.  In some places the removal of this covering involves large expenditures; in others the expense is so small as to be negligible.

Sheets, rift, and grain.-A sufficient amount of vertical exploration should be made, possibly by core drilling, in order to determine the thickness of the sheets, the width of the sap, the direction and amount of rift and grain.

Quarry site.-With these preliminaries a quarry site should be selected.  In this selection the inclination of the sheets and location of headings and dikes should be considered, as well as the amount of stripping, the location of dumps, the drainage, and the facilities for transportation.  The location of a quarry on a level tract, away from streams or shore, may entail insurmountable drainage difficulties.

Transportation.-The cost of transporting the product is obviously one of the great factors in granite quarrying.  The basis of the Maine granite industry is the location of its quarries at tidewater.  At many quarries schooners of 175 registered tonnage-that is, carrying from 300-350 long tons-are laden within 500 feet and some within 125 feet of the point where the stone is quarried.  (See Pl. XII, A.)  Notwithstanding the greater cost of transportation by rail and the necessity, in many places, of a second handling, Maine granite has found its way far into the interior, as will be seen by reference to the description of the quarries under the heading of "Product."  This is supposed to be due to the fact that the completeness of the plants and the ability of the firms in handling large contracts has more than counterbalanced the great distance of the quarry from market.  But in any case the transportation of the product any considerable distance by teams to railroad or wharf is a very serious drawback.  When the quarry is at a considerable elevation above the railroad or wharf, as at Mount Waldo and Mosquito Mountain, in Frankfort, elaborate systems of gravity rail transportation must be provided.  At each of these quarries this has involved about 1 1/2 miles of railroad track, besides special engines and great lengths of steel cable.

Plate XII-A.  Webster Quarry, on Pleasant River, at end of Winter Harbor, Vinalhaven, looking west.  Granite-laden schooner to right.  Photograph by Merrithew.

Plate XII, A.

Plate XII-B.  Paving-Block Quarry at Vinalhaven.  A "Motion."  Photograph by Merrithew.

Plate XII, B.

Drainage.-In small and newly opened quarries drainage is an insignificant matter, but as the quarry deepens it assumes importance.  Where the quarry stands at some elevation the drainage is easily disposed of by ordinary piping or siphoning, but if the quarry bottom lies below the level of the surrounding tract and if the drainage exceeds the needs of the boilers, pumping must be resorted to; but even in such places there must be some available stream or shore to carry off the water.  The amount of pumping requisite varies greatly.

Water supply.-When the needs of the boilers exceed the amount supplied by the drainage, neighboring springs or brooks are resorted to.  On small islands that are without streams or copious springs the question of water supply in large quarries is a serious one.  At one of the Crotch Island quarries water has been brought from Stonington, a mile distant at an expense of $110 a month, and at the High Isle quarry water is obtained by pumping from accumulations in the old quarry pits on Dix Island.  This required 3,900 feet of 3-inch pipe.  In order to obviate such outlays bored wells are being resorted to, by means of which it is expected that the entire drainage of these islands will be made available.  As explained on page 38, it is only the joint and sheet structure that makes granite a source of water.  The subject of well boring in granite will be discussed in a paper to be published by the United States Geological Survey.[60]  If well boring should fail to yield an adequate supply to island quarries, the condensation of sea water could still be resorted to, as in ocean navigation.

Use of explosives and wedges.-At no point in granite quarrying is more experience and judgment requisite than in the use of explosives.  The selection of the place for blasting, the size and shape of the hole, the selection of the powder, and the size of the charges are all matters requiring careful consideration.  The thickness of the sheet, the proximity of joints, the vitreousness of the stone, its rift and grain structure, the physical and mathematical laws governing the action of explosives, and the direction in which the quarryman desires to split the mass are all factors in each problem.

The mathematics of the subject will be found treated in a recent book by Daw,[61] and a general description of quarry methods will be found in a report by Walter B. Smith.[62]

The practice of foremen in the thirty principal granite quarries of Maine, as explained by them to the writer, was found to be as follows:  Vertical blast holes almost as deep as the thickness of the sheet are drilled by pneumatic steam drills along a proposed line of fracture under three sets of conditions.  The block to be loosened must be:  (A) Bounded laterally by two free ends (consisting either of two artificial channels or two joints or headings or dikes, or else one of these and one channel) and bounded the other way by one quarried face and the desired line of fracture; or (B) bounded laterally by one channel and the proposed line of fracture and the other way by a heading or joint and a free face; or (C) not bounded laterally by any free end and the other way only by the working face.  In this case after the fracture is made the two other sides in the block must be cut either by blasting or splitting.  In all these cases the boundaries of the block are the upper and lower surfaces of the sheets, and the lines of fracture must following either the rift or the grain.  Where the grain is weak it requires double the number of blast holes to effect a fracture along it that it does along the rift.  Where there is no vertical rift or grain it is impracticable to use method C, and in such cases, even with two free ends, channeling is resorted to.

Fig. 3.  Diagrams illustrating methods of using explosives in Maine granite quarries, F, face; J, joint, heading, or dike; C, channel; H, "hard-way" or "cut-off."  The round dots represent blast holes.  In diagram X the diagonal crack shows effect of not channeling on right side.  In method shown in diagram B explosives are not used along the rift, and in that of H (Hallowell granite) little or no explosive is used along the grain.

Fig. 3. Diagrams illustrating methods of using explosives in Maine granite quarries


Plate XIII-A.  Lintel for New York Custom-House, carved from even-grained coarse-textured biotite granite of Sands Quarry, Vinalhaven.  Showing adaptability for coarser sculpture.  Portion at left of head unfinished.  Photograph by Merrithew.

Plate XIII-A. Lintel for New York Custom-House

 

Exceptionally still another method is in use, which requires only one lateral joint face and one working face (besides the sheet surfaces), the line of fracture forming the third side.  But this method is regarded as hazardous by the more experienced men, for the fracture is apt to leave its direction of parallelism to the working face and swerve off diagonally to meet it.  Processes A, B, and C are illustrated in fig. 3, diagrams A, B, and C.  The case without rift or grain is marked D, and the hazardous one X.

The blast holes are usually "lewis holes," which consist of two or three contiguous drill holes, with the intervening rock chiseled out, or, where less force is required, "knox holes," consisting of a circular drill hole, with two diametrically opposite lateral vertical grooves.  The drill holes may be made divergent below.  The "channels" are about 4 feet wide and are made either by drilling blast holes in zigzag order, which are fired singly in diagonal order, or by drilling holes on both sides of the proposed channel in close order; or else the channel consists of a single row of contiguous drill holes.  This practice is found more economical than that of using a regular channeling machine.  When the stone is delicate, as in the Hallowell quarries, powder is used sparingly or not at all.  In the latter case channeling is done in two directions at 90, and the operation is completed by splitting by wedges in the third.  (See fig. 3, diagram H.)

At the Long Cove quarry of Booth Brothers and Hurricane Isle Granite Company (p. 128) mining is resorted to.  Shafts and cross tunnels are blasted out on the plan of an inverted T (T) and large quantities of powder are exploded in the ends of the horizontal parts, in order to loosen a great mass of overlying rock.

After the block has been loosened by methods A, B, or C, it is broken up into minor blocks by "splitting."  As is well known, splitting is now done almost entirely by the use of pneumatic plug drills.  The holes are 3 to 4 inches deep, three-fourths inch in diameter, and a few inches apart.  Every few feet a deeper hole is drilled.  Iron wedges are then very gradually driven in between steel side pieces called "feathers."

A difference is found in blasting and splitting granite in winter and summer. A low temperature increases the cohesiveness, but, probably in connection with water, increases its fissility where the "rift" is feeble.

It is reported that in quarries in Finland the expansive power of freezing water is regularly used in splitting.  This is in line with the ancient Egyptian use of the expansion of wet woody tissue.  A method of blasting in use in some of the English coal mines by means of the expansion of slaked lime may be susceptible of adaption to the quarrying of more delicate granites.[63]

In this connection should be mentioned the method recently adopted in the granite quarries of North Carolina of developing an incipient sheet structure by the use of high explosives followed by the application of compressed air.  (See footnote, p. 37.)

Utilization of waste.-In most of the Maine quarries the thin sheets and the waste material are worked up into paving blocks, which consume not only the smaller fragments, but blocks which are disfigured by sap or knots.  The size of these blocks differs from different cities.  The standard in New York is from 11 to 14 by 4 by 7 inches.  The flat side is cut parallel to the rift.  Paving stones are the only product of some quarries.  The drilling at such quarries is generally done by hand.  A paving-stone quarry, posting from its often simple and temporary character, is called a "motion."  (See Pl. XII, B.)  The magnitude of the paving-stone industry in Maine can be seen from the statistics on page 183.  Another use of waste is for crushed stone for macadamizing roads.  The only quarry in Maine that is provided with a stone crusher for the utilization of its waste in this way is that at North Jay.  The diabase dikes which are so inconvenient in some granite quarries could well be utilized in this way also, and would furnish a kind of crushed stone for which there might be a greater demand than for crushed granite.  The architectural use of discolored granite (sap) is in vogue at the Cape Ann, Mass., quarries, where the Rockport public library has been made of it and the unaltered granite used for trimmings.  No such thing was encountered in Maine.  That sort of waste could be cheaply supplied by many quarries.


Plate XIII-B.  Monolithic columns of coarse-textured biotite granite
quarried at Palmer Quarry, Vinalhaven,for the Cathedral of St. John the Divine,
at New York.  Length, 51 feet 6 inches to 54 feet; diameter, 6 feet.  One column in lathe.

Plate XIII-B. Monolithic columns of coarse-textured biotite granite

 

Plate XIV.  Carvings from light-gray fine-textured biotite-muscovite granite from the Stinchfield Quarry, near Hallowell, showing adaptation to delicate sculpture.

A.  Part of panel at side of entrance to New York Bank of Commerce.

A. Part of panel at side of entrance to New York Bank of Commerce.


B.  Statue erected in 1906 at the Hall of Records in New York.

B. Statue erected in 1906 at the Hall of Records in New York.


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