See also:term applied to any
See also:limestone or
See also:dolomite which is sufficiently close in texture to admit of being polished . Many other ornamental stones—such as
See also:serpentine, alabaster and even granite—are sometimes loosely designated marble, but by accurate writers the term is invariably restricted to those crystalline and compact varieties of carbonate of lime (occasionally with carbonate of
See also:magnesia) which, when polished, are applicable to purposes of decoration . The crystalline structure is typically shown in statuary marble . A fractured
See also:surface of this
See also:stone displays a multitude of sparkling facets, which are the
See also:rhombohedral cleavage-planes of the component grains . The beautiful lustre of polished statuary marble is due to the
See also:light penetrating for a
See also:short distance into the
See also:rock and then suffering reflection at the surfaces of the deeper-lying crystals . The durability of marble in a dry atmosphere or when protected from
See also:rain renders it a valuable
See also:building stone (q.v.); on the other
See also:hand, when exposed to the
See also:weather or the acid atmosphere of large cities, its surface readily crumbles . first place may be assigned to the famous Pentelic marble, the material in which
See also:Praxiteles, and other Greek sculptors executed their
See also:works . The characteristics of this stone are well seen in the
See also:marbles, which were removed from the
See also:Parthenon at Athens, and are now at the
See also:British Museum . The marble was derived from the quarries of
See also:Mount Pentelicus in
See also:Attica . Several large buildings have recently been constructed with this marble in
See also:London . The neighbouring
See also:mountain of Hymettus likewise yielded marbles, but these were neither so pure in
See also:colour nor so
See also:fine in texture as those of Pentelicus . Parian marble, another stone much used by Greek sculptors and architects, was quarried in the isle of
See also:Paros, chiefly at Mount Marpessa .
It is called by
See also:ancient writers lychnites (from the Gr . X5Xvos, a lamp) in allusion to the fact that the quarries were worked by the light of lamps . The
See also:Venus de' Medici is a notable example of
See also:work in this material . Carrara marble is better known than any of the Greek marbles, inasmuch as it constitutes the stone invariably employed by the best sculptors of the
See also:day . This marble occurs abundantly in the Apuan
See also:Alps, an offshoot of the Apennines, and is largely worked in the neighbourhood of Carrara,
See also:Massa and Serravezza . Stone from this
See also:district was employed in Rome for architectural purposes in the
See also:time of
See also:Augustus, but the finer varieties, adapted to the needs of the sculptor, were not discovered until some time later . It is in Carrara marble that the finest works of Michelangelo and of
See also:Canova are executed . The purest varieties of this stone are of
See also:white colour and of fine saccharoidal texture .
See also:Silica is disseminated through some of the marble, becoming a source of annoyance to the workman; while occasionally it separates as beautifully pellucid crystals of
See also:quartz known as " Carrara diamonds." The
See also:geological age of the marbles of the Apuan Alps has been a subject of much dispute, some geologists regarding them as metamorphosed Triassic, Liassic or Rhaetic rocks . Much of the
See also:common marble is of a bluish colour, and therefore unfit for statuary purposes; when streaked with blue and
See also:veins the stone is known as bardiglio . Curiously enough, the common white marble of Tuscany comes to England as Sicilian marble—a name probably due' to its having been formerly re-shipped from some
See also:port in
See also:Sicily . Although crystalline marbles
See also:fit for statuary work are not found to any extent in
See also:Great Britain, the limestones of the Palaeozoic formations yield a great variety of marbles well suited for architectural purposes .
- The Devonian rocks ofsouth
See also:Devon are
See also:rich in handsome marbles, presenting great diversity of tint and
See also:pattern . Plymouth,
See also:Torquay, Ipplepen, Babbacombe and Chudleigh may be named as the principal localities . Many of these limestones owe their beauty to the fossil corals which they contain, and are hence known as " madrepore marbles." Of far greater importance than the marbles of the Devonian
See also:system are those of Carboniferous age . It is from the Carboniferous or Mountain Limestone that British marbles are mainly derived . Marbles of this age are worked in
See also:Derbyshire and
See also:Yorkshire, in the neighbourhood of
See also:Bristol, in
See also:Wales, in the Isle of Man, and in various parts of
See also:Ireland . One of the most beautiful of these stones is the " encrinital marble," a material which owes its peculiarities to the presence of numerous encrinites, or stone-lilies . These fossils, when cut in various directions, give a characteristic pattern to the stone . The
See also:joints of the stems and arms are known from their shape as "
See also:wheel-stones," and the rock itself has been called " entrochal marble . The most beautiful varieties are those in which the calcareous fossils appear as white markings on a ground of grey limestone . In Belgium a black marble with small sections of crinoid stems is known as
See also:petit granit, while in Derbyshire a similar rock, crowded with fragments of minute encrinites, is termed "
See also:eye marble." Perhaps the most generally useful marbles yielded by the Carboniferous system are the black varieties, which are largely employed for
See also:chimney-pieces, vases, and other ornamental
See also:objects . The colour of most black limestone is due to the presence of bituminous
See also:matter . Such limestone commonly emits a fetid odour when struck; and the colour, being of organic origin, is discharged on calcination .
Black marbles, more or less dense in colour, are quarried in various parts of Ireland, especially atKilkenny and near
See also:Galway, but the finest kind is obtained from near
See also:Ashford in Derbyshire . From Ashford is also derived a very beautiful stone known as "
See also:rosewood marble." This is a dense
See also:brown laminated limestone, displaying when polished a handsome pattern somewhat resembling the
See also:grain of rosewood; it occurs in very limited quantity, and is used chiefly for inlaid work . The black marble of Frosterley,
See also:shire, is another Carboniferous example which owes its " figure " or pattern to the presence of large corals . With the rosewood marble may be compared the well-known " landscape marble " or Cotham stone, an argillaceous limestone with
See also:peculiar dendritic markings, due probably to the infiltration of
See also:water containing
See also:oxide of
See also:manganese . This limestone occurs in irregular masses near the
See also:base of the White
See also:Lias, or upper-most division of the Rhaetic series . It is found principally in the neighbourhood of Bristol . The arborescent forms depicted in bluish-grey upon this landscape marble
See also:form a marked contrast to the angular markings of warm brown colour which are seen on slabs of " ruin marble " from Florence—a stone occasionally known also as landscape stone, or pietra paesina . British limestones of Secondary and
See also:Tertiary age are not generally compact enough to be used as marbles, but some of the shelly beds are employed to a limited extent for decorative purposes . " Ammonite marble " is a dark brown limestone from the
See also:Lower Lias of
See also:Somersetshire, crowded with
See also:ammonites, principally A. planicostata . Under the name of
See also:Forest marble, geologists recognize a
See also:local division of the Lower Oolitic series, so named by W .
See also:Smith from Wychwood Forest in
See also:Oxfordshire, where shelly limestones occur; and these, though of little economic value, are capable of being used as rough marbles . But the most important marbles of the Secondary series are the shelly limestones of the Purbeck formation .
Purbeck marble was a favourite material with
See also:medieval architects, who used it freely for slender clustered columns and for sepulchral monuments . It consists of a mass of the shells of a fresh-water
See also:snail, Paludina carinifera, embedded in a blue, grey or greenish limestone, and is found in the Upper Purbeck beds of
See also:Swanage in
See also:Dorsetshire . Excellent examples of its use may be seen in
See also:Westminster Abbey and in the
See also:Church, as well as in the cathedrals of
See also:Salisbury, Winchester,
See also:Worcester and Lincoln .
See also:Sussex marble is a very similar stone, occurring in thin beds in the
See also:clay, and consisting largely of the shells of Paludina, principally P. sussexiensis and P. fluviorum . The
See also:altar stones and the episcopal
See also:chair in Canterbury
See also:Cathedral are of this material . Certain calcareous metamorphic rocks frequently form stones which are sufficiently beautiful to be used for ornamental purposes, and are generally classed as marbles . Such. serpentinous limestones are included by petrologists under the term " ophicalcite." The famous verde antico is a rock of this character .
See also:Mona marble is an ophicalcite from the metamorphic series of the Isle of Anglesey, while the " Irish
See also:green "of architects is a similar rock from
See also:Connemara in western Galway . It is notable that some of the " white marble " of Connemara has been found by W .
See also:King and T . H . Rowney to consist almost wholly of malacolite, a silicate of calcium and magnesium .
A beautiful marble has been worked to a limited extent in the
See also:island of Tiree, one of the
See also:Hebrides, but the
See also:quarry appears to be now exhausted . This Tiree marble is a limestone having a delicate
See also:carnelian colour diffused through it in irregular patches, and containing rounded crystals of sahlite, a green augitic
See also:mineral resembling malacolite in composition . Many marbles which are prized for the variegated patterns they display owe these patterns to their formation in concentric zones—such marbles being in fact stalagmitic deposits of carbonate of lime, sometimes consisting of
See also:aragonite . One of the most beautiful stalagmitic rocks is the so-called
See also:onyx marble of Algeria . This stone was largely used in the buildings of
See also:Carthage and Rome, but the quarries which yielded it were not known to
See also:modern sculptors until 1849, when it was redis-covered near Oued-Abdallah . The stone is a beautifully trans-lucent material, delicately clouded with yellow and brown, and is greatly prized by French workmen . Large deposits of a very fine onyx-like marble, similar to the Algerian stone, have been worked at Tecali, about 35
See also:miles from the city of Mexico . Among other stalagmitic marbles, mention may be made of the well-known
See also:Gibraltar stone, which is often worked into
See also:models of
See also:cannon and other ornamental objects . This stalagmite is much deeper in colour and less translucent than the onyx marbles of Algeria and Mexico . A richly tinted stalagmitic stone worked in California is known as Californian marble . It is worth noting that the " alabaster " of the ancients was stalagmitic carbonate of lime, and that this stone is therefore called by mineralogists "
See also:Oriental alabaster " in
See also:order to distinguish it from our modern " alabaster," which is a sulphate, and not a carbonate, of lime .
See also:Gypsum capable of taking a
See also:polish is found at Fauld in Stafford-shire and in Italy and Spain .
The brown and yellow
See also:colours which stalagmitic marbles usually present are due to the presence of oxide of iron . This colouring matter gives
See also:special characters to certain stones, such as the giallo antico, or
See also:antique yellow marble of the
See also:Italian antiquaries .
See also:Siena marble is a reddish mottled stone obtained from the neighbourhood of Siena in Tuscany; and a somewhat similar stone is found in King's
See also:County, Ireland . True red marble is by no means common, but it does occur, of bright and
See also:uniform colour, though in very small quantity, in the Carboniferous limestone of Derbyshire and north-east Stafford-shire . The red marble called rosso antico is often confounded with the porjiro rosso antico, which is really a
See also:hornblende porphyrite owing its red colour to the mineral withamite .
See also:Fire marble is the name given to a brown shelly limestone containing ammonites and other fossil shells, which present a brilliant display of iridescent colours, like those of precious
See also:opal . It occurs in rocks of Liassic age at the . lead-mines of Bleiberg in
See also:Carinthia, and is worked into
See also:snuff-boxes and other small objects . By mineralogists it is often termed lumachella, an Italian name which may, however, be appropriately applied to any marble which contains small shells . The quarries of France, Belgium, Italy and Spain, not to mention less important localities, yield a great diversity of marbles, and almost each stone bears a .distinctive name, often of trivial meaning; but in this article it is impossible to enumerate the local names used by marble-workers in, different countries to distinguish the various stones which pass under their hands .
See also:America possesses some valuable deposits of marble, which in the eastern States have been extensively worked . The crystalline limestones of western New England furnish an abundance of white and grey marble, while a beautiful material fit for statuary work has been quarried near
See also:Rutland in
See also:Vermont . A grey bird's-eye marble is obtained from central New York, and the greyish clouded limestones of Thomaston in Maine have been extensively quarried .
Of the variegated and coloured marbles, perhaps the most beautiful are those from the
See also:part of Vermont, in the neighbourhood of Lake Champlain . A fine brecciated marble is found on the
See also:Maryland side of the
See also:Potomac, below Point of Rocks . Among the principal localities for black marble may be mentioned
See also:Shoreham in Vermont and Glen Falls in New York . In 1908 the
See also:American States producing marble were, in order of value, Vermont,
See also:Tennessee, New York, Massachusetts,
See also:Alabama, Pennsylvania, Maryland, California,
See also:Alaska, N . Carolina,
See also:Kentucky, New Mexico,
See also:Missouri and
See also:Idaho . In
See also:Canada the crystalline limestones of the pre-
See also:Cambrian series yield beautiful marbles . In India we find important quarries at Makrana in
See also:Rajputana, —a locality which is said to have yielded the marble for the famous Taj Mahal at
See also:Agra . In the valley of the
See also:Nerbudda, near Jabalpur, there is a large development of marble . The white marble which is used for the delicately pierced screens called jalee work is obtained from near Raialo, in Ulwar . (F . W . R.*) Petrography.—Marbles are uniformly crystalline, and hence have no bedding or schistosity which would tend to make them fissile, 678 but are entirely massive and
See also:free from grain .
The microstructure of pure marble is comparatively
See also:simple . In thin sections they are seen to be built up of somewhat rounded grains of
See also:calcite, fitting closely together in a
See also:mosaic; very rarely do any grains show traces of crystalline form . They are colourless and transparent, and are usually traversed by a lattice-work of sharply defined cleavage cracks, which correspond to the rhombohedral faces . In polarized light the colours are pinkish or greenish white, or in very thin sections iridescent because the mineral has a very strong
See also:double refraction . They may also be crossed by bars or stripes, each of which indicates a twin
See also:plate, for the crystals are usually polysynthetic . This twinning may be produced by pressure acting either during the
See also:crystallization of the rock or at a later
See also:period . The purest marbles generally contain some
See also:accessory minerals, and in many of these rocks they form a considerable proportion of the whole mass . The commonest are quartz in small rounded grains, scales of colourless or
See also:pale yellow mica (
See also:muscovite and
See also:phlogopite), dark shining flakes of
See also:graphite and small crystals of
See also:pyrites or iron oxides . Even fine Carrara marble leaves a
See also:residue of this sort when dissolved in acid . Many marbles contain other minerals which are usually silicates of lime or magnesia . The
See also:list of these accessories is a very large one .
See also:Augite is very frequent and may be white (malacolite) or pale green (coccolite, sahlite,
See also:diopside) ; hornblende occurs as white bladed
See also:tremolite or pale green actinolite; feldspars may be present also, such as
See also:orthoclase, or more frequently some
See also:plagioclase such as
See also:labradorite and
See also:anorthite; scapolite (or wernerite) ; various kinds of garnet ;
See also:spinel, forsterite, periclase,
See also:zoisite and
See also:epidote, chondrodite,
See also:sphene and
See also:apatite may be mentioned as typical accessory minerals .
The presence of metalliferous minerals such as
See also:galena, grey or red
See also:silver ores,
See also:blende, antimonite, chalcopyrite,
See also:molybdenite, cassiterite, usually indicates impregnation by ore-bearing solutions, especially if these substances occur in workable quantities . The rubies ofY
See also:Burma are found in crystalline lime-stones and are constantly accompanied by precious spinel (or balasruby) . These minerals represent impurities in the
See also:original limestone which crystallized at the time that the marble became crystalline . The silicates derive their silica mainly from sand or infiltrated siliceous deposits; the alumina represents an admixture of clay; the iron came from
See also:limonite or hematite in the original state of the rock . Where the silicates bulk largely because the original limestone was highly impure, all the carbonic acid may be driven out and replaced by silica during the
See also:process of recrystallization . The rock is then a talc-silicate rock, hard, tough, flinty and no longer readily soluble in acids . They are sometimes fine-grained hornstones (known as calc-silicate hornfelses) . Where white minerals predominate (
See also:wollastonite, tremolite, feldspar) these rocks may have a close resemblance to marbles, but often they are green from the abundance of green augites and amphiboles, or brown (when garnet and vesuvianite are present in quantity) or yellow (with epidote, chondrodite or sphene) . Decomposition induces further changes in colour owing to the formation of green or yellow serpentine, pale green talc, red hematite, and brown limonite . Most of the coloured or variegated crystal-
See also:line marbles have originated in this manner . Often bands of calcsilicate rock alternate with bands of marble, and they may be folded or bent ; in other cases, nodules and patches of silicates occur in a
See also:matrix of pure marble .
See also:Earth movements may shatter the rocks, producing fissures afterwards filled with veins of calcite; in this way the beautiful brecciated or veined marbles are produced .
Sometimes the broken fragments are rolled and rounded by the flow of the marble under pressure and pseudo-conglomerates or " crush conglomerates " result . In other cases the banding of the marble indicates the original bedding of the calcareous sediments . Crystal-line limestones which contain much mica may be called cipollins; in them quartz, garnet and hornblende often also occur . The ophicalcites are marbles containing much serpentine, which has been formed by the decomposition of forsterite,
See also:olivine or augite . The much-discussed Eozoon, at one time supposed to be the earliest known fossil and found in Archaean limestones in Canada, is now known to be inorganic and to belong to the ophicalcites . Many marbles, probably all of them, are metamorphosed lime-stones . The passage of limestones rich in fossils into true marbles as they approach great crystalline intrusions of granite is a phenomenon seen in many parts of the
See also:world; occasionally the recrystallization of the rock has not completely obliterated the organic structures (e.g. at Carrara and at
See also:Bergen in Norway) . The agencies which have induced the metamorphism are
See also:heat and pressure, the heat arising from the granite and the pressure from overlying masses of rock, for these changes took place before the granite cooled and while it was still deeply buried beneath the surface . In 18o6
See also:Hall described a series of experiments proving this . He enclosed
See also:chalk in a
See also:barrel securely plugged and heated it to a high temperature in a
See also:furnace . Carbonic acid was given off by the chalk and produced a great pressure in the interior of the
See also:tube . After slow cooling the mass was found to have become converted into granular crystalline marble .
As rocks which have undergone changes of this kind are commonest in the
See also:oldest and deepest layers of the earth's crust, most marbles are Palaeozoic or pre-Cambrian . They occur very often with mica
See also:schists, phyllites, &c., which were beds of clay alternating with the original limestone . Formerly it was supposed that some of these marbles were crystalline sediments or even igneous rocks, but the tendency of modern geology is to assume that they were ordinary limestones, many of which may have been fossiliferous . In regions where the sedimentary rocks have been converted into schists, gneisses and granulites, the limestones are represented by calc schists, cipollins and marbles . Often no granite or other intrusive rock is present which may be regarded as the cause of the metamorphism . The marbles are often banded or schistose, and under the microscope show crushing and deformation of the component crystals, such as would have been produced by the earth pressures which accompany rock-folding . These crush structures have been obtained experimentally in marbles subjected to great pressures in
See also:steel cylinders . In the recrystallization of these limestones the
See also:action of igneous intrusions may have played no part, but the rise of temperature and increase of pressure due to the folding of great rock masses have probably been the operating causes . This type of metamorphism has been distinguished by the name marmarosis (Sir A . Geikie, Text
See also:Book of Geology, 1882) . For descriptions of ancient marbles see F . Corsi, Delle pietre antiche (Rome, 1845) ; M .
See also:Porter, What Rome was built with (
See also:Oxford, 1907), and for marbles in general consult E .
See also:Hull, Building and Ornamental Stones (1872) ; G . P .
See also:Merrill, Stones for Building and Decoration (3rd ed., 1905, New York) . (J . S .
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