( Fr- marbre, calcaire,
Nor- marmor, kalkstein, dolomitt; Rus- )
MARBLE, LIMESTONE, and DOLOSTONE (See also FOSSILIFEROUS ROCKS and TRAVERTINE entries.)
A. Marble cabochon (greater axis - ca. 3.5 cm). Brecciated yellow, black and white marble from Italy. Smithsonian Institution collection. (photo by Lee Bolton)
B. Marble cabochon (greater axis - ca. 2.5 cm). Black and white marble from Spain. Smithsonian Institution collection. (photo by Lee Bolton)
C. Marble figure, "Sky King" (length, left to right - ca. 100 cm), sculpted from Carrara marble by Dennis R. Christy. Sculptor's personal collection. (© photo by Dick Dietrich)
D. White calcite-veined limestone (bottom width - 20 cm; height -10.1 cm) thought to have been carved in China. Smithsonian Institution collection, added 1892. (© photo by B. Chromy)
DESCRIPTION: Properties of calcite
and dolomite, the chief mineral constituents of these rocks, precede
general properties for the three rocks.
Dolostones are diagenetic, and/or possibly
sedimentary, rocks. Dolostone is used in this document as part of
my mission to discontinue the dual application of the mineral name to
both the mineral and the rock. This breaks with the widespread traditional usage whereby rocks made
up largely of the mineral dolomite are also called dolomite.
(Alternatively, either rock dolomite or dolorock would seem more
appropriate terms than continuing the dual usage.)
Colors - white, gray, tan, reddish, bluish, greenish, brownish
H. 3½ - 4
Light transmission - translucent (in thin pieces) to opaque
Luster - dull to pearly(polished)
Breakage - irregular to subconcoidal
Miscellany - grain size varies from microscopic to coarse granular; see the following NOTE.
Although geologists restrict application of the term marble to metamorphosed carbonate rocks, in the marketplace marble is frequently applied to any predominantly carbonate rock -- including coarsely crystalline limestones and dolostones as well as their metamorphosed products (i.e., marble) -- that take a good polish. The widely used stylolite-bearing "Tennessee marble," which is a coarsely crystalline (recrystallized!) dolostone that has NOT undergone metamorphism, is an example of the broader marketplace application of the term. Although this broader usage has been applied for the most part by dealers in ashlar and other decorative facings stone, more recently, this extended nomenclature has also been applied by dealers in ornaments made from such rocks.
Yet another nomenclature problem relating to marbles and other carbonate-rich gemrocks exists: Some travertine deposits, especially speleothems, have been called marbles in the marketplace. Probably the best (worst?) example relates to the many designations that fall into a group that may be called, for lack of a better name, the onyx marbles --e.g., Mexican onyx. These rocks are neither marble nor onyx according to definitions accepted by most geologists (see TRAVERTINE entry).
In the marketplace, such things as colors, patterns of colors, former use, and/or some locality of occurrence are frequently applied as adjectives preceding the name marble or even as "bald names" for individual marbles. Many of the names are of Italian origin, which reflects the fact that Italy has had such a long history in the production of diverse marbles.
Examples of names given marbles, limestones, and dolostones used as gemrocks follow:
USES: Because they are relatively easily worked and many things fashioned from them are attractive, these three rocks, particularly marble, have been used widely as gemstones as well as for statuary, ashlar, tombstones, altars, steles, etc. Examples of gemrock use are beads, cabochons and carved stones (including cameos) for jewelry; carvings (e.g., fetishes, figurines and ornaments); and functional pieces such as bookends, bases for lamps and desk sets, decorative cases for clocks and kaleidoscopes, cutting boards and lazy susan tops and both stoppers and partly hollowed-out cylinders for chilling bottles of wine. The just mentioned cameos include both "solid black" and "solid white" marble cameos (Crowningshield, 1960) and so-called "lava" cameos fashioned from fine-grained gray and borownish yellow limestone (Liddicoat, 1963). Also, especially in the past, bituminous limestone was used as the base for inlay pieces, and chalk, which is limestone, has been used for carving, especially by novices. In addition, marble and limestone have been stained blue and marketed as turquoise (Crowningshield, 1963). ***Marble egg-shaped masses have been marketed for placing in places where owners want their hens to lay their eggs -- e.g. within their coops -- and also as parts of decorative items -- e.g., a "Wren's nest ..." described as an "appealing table decoration." A somewhat peculiar use: Marble, has been dyed pink and fashioned into beads to imitate opal from the Peruvian Andes (Milisenda, 2006).
OCCURRENCES: Typical limestones are relatively common chemically or biochemically deposited sedimentary rocks in marine sequences. Most dolostones are diagenetic rocks, also occurring in marine sequences. True marbles occur where sedimentary rock sequences including limestones and/or dolostones have undergone metamorphism of the type usually referred to as regional metamorphism.
NOTEWORTHY LOCALITIES: True marbles are widespread: Italy is a major producer; in the United States, the marbles of Proctor, Rutland County, Vermont are well known; the Cotham Marble (an argillaceous limestone) from near Bristol, England is a well-known source of landscape marble; Caymanite is recovered from the eastern end of Grand Cayman and reportedly also from Cayman Brac (Koivula, Kamamerling & Fritsch, 1994, p.193); fine white dolomitic marble occurs in Dutchess County, New York. A few localities are noted for other marbles as well as for certain limestones and dolostones along with the appropriate listings under the OTHER NAMES subheading.
REMARKS: The roots and changes
through the ages and languages that led to the word marble are
extremely complex and not fully clear -- see QED summary. The
origin of the term limestone is quite apparent; that of dolostone
is based on its consisting largely or wholly of the mineral dolomite,
which was named in late 18th century for the French geologist and
mineralogist M. Déodat de Dolomieu.
For untold decades, marble -- especially white or nearly white marble -- has been dyed one or more colors and marketed as " ... marble" or even " ... onyx" with the ellipsis replaced by the imposed color or colors with NO indication that the appearance is anything but natural, and in the case of the "... onyx" no indication that it is marble. In addition, some marketplace marbles have been impregnated by such things as paraffin or plastics, and a few have been touched up with paint and/or dyes to make them appear more nearly homogeneous.
Two marbles -- Carrara and Parian marbles -- are mentioned in the "Dictionary of gems and gemology ..." (GIA, 1974) as having been used for fashioning of diverse items since ancient times; my recollection is that during a visit to the Vatican the guide said that Michelangelo's pietà and several of his other works were sculpted from Carrara marble. Some landscape and ruin marbles have been used as the "canvas" upon which artists have painted -- see, for example, those that illustrate literary works of Ariosto, Boiardo and Dante (Caillois, 1985). Indeed, these marbles also have been used for untold ages as decorative stones -- e.g., as tiles for interiors and landscape accents, for sculptures and headstones and even as ashlar -- this, despite the fact that marble is ill-suited for some of these uses, especially when put out-of-doors in certain climatic environments. Two examples of such ill-conceived use are: 1.In some areas -- especially where there is acid rain (and dew) -- marble undergoes relatively rapid chemical weathering; this means, among other things, that inscriptions on monuments placed in such places become indecipherable after exposure over relatively short periods. and 2.Some marble tends to "flow" under its own weight, which in some cases creates hazardous conditions (Titamgim, 1992).
A surprizing, at least to me, ancient use
marble was as disks (15-20 cm in diameter), many with pupils and irises
on them, as ophthalmoi (eyes) on ancient vessels used in the
Mediterranean, Indian Ocean and other large waterways. These
"eyes", fastened on each side of a prow was "to give life to a
ship or to help it
see its way through the waves ... [They were] common to many
cultures from Portugal to India" (Bass, 2002).
"The Standard of Ur, made of shell, lapis lazuli
and red limestone [my emphasis] [that intricately] depicts a
banquet on one side and a battle on the other ... [which was] made in
BC" is illustrated on page 21) of the July/August 2003 issue of "Saudi
Marble is the state rock of Alabama, Colorado(?) and is one of three state rocks of Vermont; limestone (though not as a gemrock per se) is the state rock of Tennessee and the state stone of Indiana?.
Attention is directed to the quotation from the Preface of The Marbles and Granites of the World (Grant, 1955) given in the second paragraph under the REMARKS subheading in the GRANITE entry.
***Bonded marble, bonded stone, cast
stone, cultured marble etc. - fine particles of ground or
crushed marble and/or limestone bonded by a polymer, resin or, rarely,
fiberglass. All apparently consist of more than 75 percent, and
most of more than 90 percent, of the marble and/or limestone
particles. Some of these materials are marketed with names such
as Bonded ... Marble, with the ellipsis replaced by the name of the
constituent marble or limestone -- e.g., Bonded Carrara Marble;
others have been given marketplace names such as "Athena marble" and
"oxolyte." Most of these simulants have homogeneous
textures; some have pigments added so desired colors and/or color
patterns (e.g., marbleized appearances) are produced; all may be
cast (i.e., poured into molds). The major use of these
materials is for such things as bathroom fixtures, fireplaces, statues
(including replicas of famous works) and birdbaths; some have
been carved or sculpted. (I have been reminded, however, that
sculptors who use such materials in lieu of natural marble are
considered to be "amateurs or neophytes who don't know how to
deal with the inhomogeneities [found in many natural marbles],
something that 'real sculptors' consider an important aspect of their
art." Statuettes, reliefs (e.g., wall plaques) and diverse
ornaments and curios made -- either cast or sculpted/carved -- of these
simulants are advertized in several specialty house catalogs.
Fortunately, they are usually noted as
consisting of, for example, cultured or faux marble so potential and
buyers know the items are not marble per
se. - [handlens observation
for anyone familiar with marble etc.
to see that these materials
***Glass and porcelain that have been marbleized
have been fashioned into decorative ornaments such as vases, and some
have been marketed with misleading descriptions such as
a recently advertized "red marble vase." - [All have hardnesses greater
than marble (etc.) and lusters of most are
noticeably higher than
those of even highly polished marbles(etc.).].
***Hydrostone (hand cast alabaster and limestone plaster) - same uses as Bonded marble (q.v.). - [inferior hardness of constituent dust; Does not effervesce with dilute HCl.].
***Incolay stone -
described as "a complex combination of quart[z] based minerals such as
Rose Quartz, Sapphire Blue, Sardonyx, Carnelian, Onyx and Banded Agate,
combined ..." (e.g., www.cowboyindian.com). Several colors (etc.)
of this material have been fashioned into all sorts of decorative
ornaments and curios, most of which include white cameolike features
atop the overall material. Thus, this material could be listed as
a simulant for a few other gemrocks as well as for marble. It is
listed here because of all the colors and patterns I have seen or seen
illustrated, only a few rare marbles are the only natural
materials with which I think it might be confused. - [Observation
should suffice; also, some constituents give it an
effective hardness that is greater than that of marble.].
Slate bearing painted
designs have been substituted for "Ashford Black Marble" inlays. -
[A reversal of roles is the marketing
as dyed dolomite (and other carbonates such as magnesite) as turquoise
(McClure, Kane and Sturman, 2010 -- recorded with a bald reference so I
could not check it or give it here).]
REFERENCES: No general reference. Grant, 1955.
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