CORALS*
(Fr-corail; Ger-Koralle; Nor-korall; Rus- коралл)



A. Coral.  Precious coral (Corallium rubrum (Linnaeus, 1758)) in a Mediterranean cave.  (© photo by Peter Dyrynda, from www.solaster.net)


B. Coral.   Precious coral (Corallium rubrum (Linnaeus, 1758)) from Italy (height - 4.9 cm). Ariel.  (© photo by Jeffrey A. Scovil)
C. Coral.  Black coral rough. Genus and species, geographic source, size and other information not supplied. (© photo furnished by Peter Rohm, Rohm GmbH & Co Kg, Linz, Austria)
DESCRIPTION: Phylum Cnidaria (=Coelenterata), Class Anthozoa:  The diversity of corals is manifest by forms with widely known common names such as brain corals (Diploria and Mændrina), organ pipe coral (TubiporaI), precious coral (Corallium) and chain coral (Halysites), which is extinct.  In modern seawater:  Skeletons secreted by scleractinian corals (the "hard [or stony] corals") consist chiefly of aragonite;  skeletons of some "soft [octo] corals" are chiefly high-Mg calcite with small amounts of calcium phosphate [bioapatite?] (Justin Ries, personal communication, 2006);  skeletons of antipatharian corals consist of  horn-like proteinaceous material(s), variously recorded as antipathin, chitin, conchiolin,  gorgonin and/or keratin.  Although coral skeletons with each of the just mentioned compositions have been used in fashioning decorative items, most of the following properties are for the corals most widely recognized for their use in jewelry and/or decorative pieces -- i.e., so-called  precious coral and black coral. 
     Colors - White, red, pink or orangy pink, blood-red, “black" (i.e., intense black to brownish black), and rarely yellow, bluish or violet, with some exhibiting more than one color -- e.g., some chiefly white coral exhibits small, irregular zones that are pink, orange or pinkish orange.    "Corallium rubrum [(Linnaeus, 1758)] is pure red with no white spots, while Corallium japonicom[???] and Corallium elatius[Ridley, 1882] ... always have some white in them [Initial upper case letters and italics given on scientific names were not in original article.].  And the difference between these two is that japinicum is shiny like glass, while elatius is dull." (Peter Rohn per Yonick, 2003, p. 8)
     H.  2½ - 4:  Red and white coral - 3 - 4, increasing with Magnesium carbonate content;  black coral - typically 2½ - 3.
     S.G.  2.60 - 2.72 for carbonate corals, with 2.65 +.05, recorded for red coral;  1.32-1.4, for black coral.
     Light transmission - semitranslucent to opaque  
     Luster - dull to subvitreous;  see also last sentence under Colors.   
     Breakage - uneven to splintery
     Miscellaneous -  Red and white coral effervesce(fizz) vigorously with dilute (10 per cent) HCl;  black, blue and other keratinous corals do not.  Precious coral is striated along the length of its "branches" and exhibits concentric layers in sections that transect the branches.  (When viewed microscopically, the layers can be seen to be made up of alternating red (of diverse hues) and nearly white layers, each of which consists of fine fibers that are nearly perpendicular to the layering.)  Black coral skeletons are relatively flexible and when heated by, for example, a hot point emit an aroma that resembles that of salty burnt hair.

OTHER NAMES:  The following are names noted here and there in the literature with examples of references given for most of them.  Other names that are noted as used, but for which I have found no descriptions, include scotch (does this refer to coral of Scotch Banks near St. Croix?) and magai (see, however, page 10, bottom left photograph and caption on the great, so far as coral is concerned web site <http://medivia.sele.it/Fototeca.asp?Pagina=10&ImmaginiPerPagina=15&Contenuto=Coralli&Lingua=INGLESE>);  If I find additional definitive information about the application of these terms I will add it in the future.
   (Several additional names have been applied, especially in the market place, to coral and coral substitutes -- see, for example, http://www.rings-things.com/gemstone/c.htm.)

USES: Kunz (1913, p.69) notes that  "for twenty centuries or more [coral] was classed among the precious stones."   Hänni (2005, p.6.), reference to today notes "Coral is a particularly fascinating gem material.  It incarnates our longing for summer, sun and oceans. And coral is coming back into fashion."  Virtually all of the coral Kunz was alluding to was what is now called precious red coral (Corallium rubrum Linnaeus, 1758) from the Mediterranean.  Today, that red coral along with the closely related pink coral (Corallium --Cuvier, 1798-- spp.) and "other" red corals, for which species names have been suggested for animals that are likely subspecies, from some localities in the western Pacific continue to be used.  And, the hard parts of several other corals and related animals -- all marketed as coral(!) -- are also harvested for use in jewelry and diverse decorative pieces.  Examples of these other corals are:  Bamboo coral (Lepidisis olapa Muzik, 1978 and Acanella gregorii  Gray, 1870);  black coral (Antipathes --Milne-Edwards & Haime 1857-- spp., including A. dichotoma Pallas, 1766 and A. grandis Verrill, 1928 and also Myriopathes ulex (Ellis & Solander, 1786) and Cirrhipathes anguina (Dana, 1846);  blue coral (Heliopora coerulea (Pallas, 1766)); and gold coral (Callogorgia elegans Gray, 1858 and Parazoanthus --Haddon and Shackleton, 1891-- sp. (widely referred to as Gerardia sp, a "not accepted" name), Primnoa resedaeformis (Gunnerus, 1763) and Primnoa willeyi (Hickson, 1915).  In addition, several white corals (order Scleractinia) are used rather widely in so-called summer jewelry, diverse decorative items (e.g., Figure C) and as showpieces.   Corals of two orders and seven species are listed as "corals in trade" in the fine summary of The Australian Gemmologist (2004), a publication (web site)  that is well worth reviewing by anyone interested in corals used in jewelry etc. -- among other things it includes descriptive material and fine photographs of bamboo, blue and gold corals, which are  used in jewelry etc. but only mentioned here. 

 A few specific uses of corals follow:
    Jewelry -- beads, bracelets, necklaces, pendants and pins (including cabochons, cameos, carvings and uncut pieces), rosaries, etc.   One well-known use seems rather surprising (at least from the geographic standpoint):  Many Amerindian artists of the south-western United States, include red coral as a constituent of their multi-material jewelry -- see, for example, Chalker (2004);  in any case, the contrast of colors between, for example, red coral and turquoise do provide a special appeal for many of these pieces.

 
                                                                        


C. Coral.  A. Precious coral earrings ...  B. Black coral beads ... -- General, Species, sizes, geographic sources not divulged.  (© photos by Peter Rohm, Rohm GmbH & Co Kg, Linz, Austria)

    Carvings -- for brooches, pendants, ojimes, snuff bottles, handles of cutlery, etc.
    Miscellany -- talismans and all sorts of decorative purposes:  Diverse corals are used to adorn shelves (etc.) in homes, offices, restaurants, ..., especially in seashore regions;  handles for canes, umbrellas, etc.;  mobiles;  and such things as flywhisks, several of which were apparently made during the Bronze age are now coveted as decorative items (Dubin, op.cit., p.137).  Branching so-called stone corals are used widely in acquariums.



D. White coral. Mushroom coral ( ? Heliofungia actiniformis (Quoy & Gaimard, 1833)   OR   Scolymia wellsii Laborel, 1967 ?) -- diameter - 8 cm.  In Hawaii, where this piece was purchased, a similar mushroom coral is called ko'a-kohe   (© photo by Dick Dietrich)

In addition to the above noted uses, corals are frequently integrated with other materials, such as sea shells, for some jewelry and ornamental pieces.

OCCURRENCES & NOTEWORTHY LOCALITIES: Corals used in jewelry, decorative pieces, etc. are recovered in several ways.  Examples are while beach combing, by SCUBA divers, with deep tangle-net dredges, and using submersible craft.  The type of coral, the amount to be harvested and, therefore, the depth and mode of occurrence are major controls of which procedures used or required. These aspects, which are well described in several publications (e.g., Webster, 1975), are not covered here.

Precious (red) coral grows attached to all sorts of objects -- e.g., rock, stone, large shells, other corals, bones and even man-made things such as shipwrecks -- and commonly grows at or approximately right angles to the substrate;  that is to say, its growth is not controlled by gravity.  Much fine quality red coral has come from the Mediterranean -- e.g., offshore from Algeria, France, Italy, Morocco, Sardinia, Spain, Tunisia and the islands of Corsica, Sardinia and Sicily, -- where it has been recovered, largely by dredging, for untold decades.  It also has been recovered offshore from Japan, Malaysia and the Philippines, where most of it has apparently been similarly "fished."  In addition, Shipley (1951) lists the Persian Gulf and Australia as major sources of precious coral, and Yonick (2003) adds Hawaii, Mexico, and the coast of Africa in the Red Sea.

Black corals -- and, it should be noted that some rather diverse species (some of which are not coral, per se!) have been so-named in the world of gems and decorative items -- have been recovered here and there from each of our earth's four oceans and some of its seas, are particularly common in the Indo-Pacific region and the Caribbean, where coral reefs have been the major source.  Taiwan and the Philippines have tended to be the dominant exporters, but the Great Barrier Reef of eastern Australia is perhaps the best-known source.  And, relatively large amounts are harvested off Hawaii, where black coral "appears to have first been found in 1958 off the island of Maui." (Webster, 1975, p. 503)

Coral reefs occur in relatively shallow waters fairly close to the equator, which reflects the fact that growth of these corals appears to require a certain amount of light, temperatures that stay above ~16°C. (60°F), and salinities greater than 27,000 ppm. One cannot help but wonder, however, how Global Warming will affect, or perhaps already has affected, at least some coral growth, eh(?)!

 REMARKS:  The designation coral appears to come from the Greek κοράλλιον via the Latin corrallium ...  I have been told that originally the name was applied only to red (precious) coral -- i.e., that it was applied only later to other corals;  to date, I have found  no documentation to support this contention, although it seems quite possible considering where red coral has been found and used.  Also of interest, at least etymological, black coral belongs to the order Antipatharia, apparently rooting from early thoughts about its therapeutic effects -- i.e., anti  (Latin - against) plus pathes (Latin - disease). 

Some coral, particularly bamboo coral but also precious coral, has been dyed in order to obtain certain desired hues and/or an homogenous appearance;  most dyes can be detected by acetone, which removes or reduces the intensity of the added colors.  In addition, some white coral has been bleached in order to give it its appearance.  Also, "Pink coral is commonly impregnated with colorless wax;  and orange coral is often stabilized with plastic to improve its color and durability." (Yonick, 2003)   "A variety of techiniques -- including magnification, exposure to acetone, and Raman analysis -- can determinie if the color of a piece of ..[pink-to-red] cirak us dyed." (Smith et al., 2007)  More recently, soft coral that has been painted, rather than dyed, has been marketed as, for example, beads (Choudhary, 2013) ;  the paint was, of course, added after the beads were shaped. 

Care:  Some coral jewelry is relatively easily broken (Figure C, left).  Some may be discolored as the result of contact with, for example, perspiration;  so, it is best worn over a blouse or sweater. Apparently slight discolorations, especially of white coral, can be removed by hydrogen peroxide.  Acids -- even weak acids such as vinegar --  will attack carbonate corals, so should never be used.  And, "some of the cleaning detergents will be detrimental to the surface of coral." (Webster, 1975, p. 503)

The following is among several attributes suggested for coral: "To still tempests and traverse broad rivers in safety was the privilege of one who bore either red or white coral with him.  That this also stanched the flow of blood from a wound, cured madness, and gave wisdom, was said to have been experimentally proved." – from Kunz (1913, p.68), who cites as his source "Albertus Magnus, 'Le Grand Albert des secretz des vertus des Herbes, Pierres et Bests.  et sultre livre des Merveilles du Monde, d'aulcuns effetz causez daulcunes bests,' Turin, Bernard du mont du Chat (c. 1515). Liv. ii, fol. 9 recto." 

The fact that coral has long appealed to humans is apparent from the following from Pliny the Elder (Book XXXII, Chapter 11, paragraphs 1 & 2): "In the same degree that people in our part of the world [Rome] set a value upon the pearls of India ... do the people of India prize coral ...¶ The reddest coral and the most branchy is held in the highest esteem."  Attention is directed to the illustration of "Islamic coral prayer beads inlaid with silver, probably made in Istanbul during the nineteenth century" given by Dubin (1987, p.83).
   
As a geologist, I found it most interesting in the mid 1950s when Joe Wells told me that growth banding preserved in some fossil corals he studied indicate that during the Devonian (~415-360 my B.P.) the Earth's year was about 400 days long (see Wells, 1963).  Subsequently, this information has been 1. corroborated by astronomical estimates indicating that the Earth's rotational rate is decreasing ~0.002 seconds per century, and 2. extended to estimate of the number of months and days per month in the 400-day year. 

Although during Medieval times red coral was thought to strengthen the heart, a recent, and more pertinent use seems to be of real medical import:  "A few stony coral species are being used in certain surgical procedures.  Because their system of appropriately sized, interconnected pores is rapidly infiltrated by human blood capillaries and osteoblasts, for example, small pieces of coral are now being used for human bone grafts, particularly in face and jaw reconstruction, and in arm and leg surgery.  Coral skeleton has even been used to repair bird wing fractures.  The grafts become firmly anchored to the adjacent bone and, eventually become completely replaced by normal bone tissue.  Even more remarkably, small coral implants are being used to improve the degree to which artificial eyes exhibit natural movement.  A piece of coral is implanted into the patient's eye socket and soon becomes invaded by blood vessels and eye muscles.  Once connected to the coral implant, the artificial eye can be moved almost as naturally as a real eye.  Before transplantation, [however,] the coral grafts are chemically converted from calcium carbonate to a form of calcium phosphate (hydroxyapatite) compatible with human bone tissue." (Pechenik, 2005, p.119).

Use of coral for fashioning jewelry, curios and other decorative items led to excess harvesting and consequently to the introduction of rather strict regulations for harvesting coral reef regions under the Convention on the International Trade of Endangered Species (CITES).  Although most occurrences of red and pink corals are not affected by these regulations, virtually all occurrences of black coral are affected because its major source has been coral reefs.  Although the United States of America does not formally recognize the pertinent CITES regulations, it does appear to be managing the Hawaiian harvest of black coral relatively well by imposing a minimum size restriction (etc.) for the coral that can be harvested (UN Atlas..., 2000-2002).  Additional information about this aspect of coral harvesting and use is given in several publications -- e.g. Grigg, 1994;  Dietz, 2000; and Rohm (per Yonick, 2003);  the three citations give comments (and advice) that express rather different viewpoints. 

"To Precious To Wear" is a so-to-speak slogan applied to the continued harvesting and use of red and pink coral in jewelry.  The plea is made to stop "the extraction of red and pink corals from deep-water sources  . . . [which is] one of the greatest threats to deep-water reefs." (Carmona, Cole and Marks, 2011)  The authors make this plea because "Historically, an estimated nine million marine species, or a third of all marine life, lived on the shallow-water coral reefs.  But corals and coral reefs throughout the world are being threatened by climate change, ocean acidification, pollution, overfishing ..." (ibid.)

Black coral was adopted as the State gemstone of Hawaii in 1987.

SIMULANTS:  One somewhat anomalous situation exists so far as coral simulants:  branches of, for example, bamboo coral have been dyed and marketed as precious coral.  In addition, it seems only prudent to mention that the following list could include several additional materials, especially for black coral:  Special attention is directed to the COAL, JET, OBSIDIAN and ONYX entries in the GemRocks folder on this web site because certain varieties of each of these materials and several of their simulants might very well be used to simulate black coral.  Another relatively common substitute consists of one of several diverse cores  with veneers the consist largely of slices of coral;  these composites seem to be especially common as pieces that resemble carvings -- see, for example, Choudhary (2014). .

Akori -  As noted under OTHER NAMES, this name has dual connotations, the second of which is its application to coral substitutes "such as rock, glass and pearl with little nacre." - [see Glass and Pearl on this list.].

***Bakelite - Pink and red bracelets and necklaces that resemble coral -- but recorded to be bakelite, celluloid or lucite -- are marketed rather widely (e.g., Sassy..., 2001-2006). - [Close observation suffices;  hot-needle test gives formaldehyde odor -- BUT, see statement about this test in glossary.].  

Bone - "burnt and coloured red" (e,g., Bauer, 1913, p.615). - [superior hardness - H. ≽ 5½ ].

***Celluloid -  See bakelite. - [Close observation suffices; hot-needle test gives vinegar odor -- BUT, see statement about this test in glossary.].  

***Ceramics - mentioned by Yonick (2003). - [Close examination suffices.].

Clay, baked (black, smooth, subvitreous luster) - Some black clay necklaces roughly resemble black coral necklaces;  their appearance is virtually the same as the widely known ocarinas and whistles of Central America. - [Macroscopic examination suffices.].

Conch shell - Pieces have been reported to have been sold as genuine pink coral (Crowningshield, 1959).- [Both luster and texture, as seen with hand lens, are characteristic and quite different from that of coral.].

Coralline - aniline-dyed red chalcedony. - [superior hardness - H. 6½ - 7].

***Galalith - a casein plastic sometimes used as a simulant for coral  (Bauer, 1913, p.615). - [lower specific gravity; gives odor of burned milk with hot-needle test -- BUT, see statement about this test in glossary.].  


***Gilson "Synthetic coral"  -- Gilson product sometimes called imitation coral. - [Close observation suffices -- has grainy texture.].  

***Glass - a use suggested by Shipley (1951) -- see  Akori. - [superior  hardness - H.~5½].

Gypsum - either naturally or dyed red  (Bauer, 1913, p.615). - [inferior hardness - H. 2;  does not effervesce with dilute HCl.]. 

Horn - has been used as a simulant for black coral. - [Close examination may suffice, but for some pieces differentiation may require consulting a professional expert.].

Ivory - Walrus ivory is recorded (Ahrens, ca. 1986, p. 24) to have been used to "imitate" coral. - [Close examination should suffice.].

Limestone (dyed) - mentioned by Yonick (2003). - [Close examination suffices.].

***Lucite - see bakelite.

Marble (for "precious coral") - "mixed with isinglass [mica] and coloured with cinnabar or red-lead" (Bauer, 1913, p.615)- [Close observation suffices.].
             (for white coral) - "a necklace of graduated white to light-pink opaque beads resembling white coral proved to be stained marble" and "With the reduced supply of desirable white coral for summer jewelry, it is possible that marble may become a substitute” (Crowningshield, 1964). - [Close observation suffices.].

Pearl (i.e., "pink conch pearl") - Although noted as one of the materials used and called "Akori", this seems to me to be an unlikely simulant.  Among other things, in most cases and places, at least today, any pearl worthy of the name would be considered more valuable than coral. - [general structure/texture and luster; higher specific gravity]. 

***Plastics - Diverse plastics --e.g., nylon -- have been produced to replicate diverse coral for use in jewelry. - [Close examination suffices.].

***Porcelain - a common substitute. - [Close examination suffices.].

***+ Reconstructed coral - mixture of powdered coral plus a binding material, and commonly dyed (Yonick, 2003). - [Close examination suffices.].

***Rubber and gypsum mixtures - such, apparently colored red with cinnabar or red lead, are recorded by Webster (1975, p. 503). - [Close examination suffices.].

***Sealing wax - red variety. - [will melt readily if probed by, for example, a hot needle  -- BUT, see statement about this test in glossary.]. 

Vegetable ivory - "probably the most attractive counterfeit of coral ...but this may be identified by the dot-like cell structure seen when the surface is examined by a lens." (Webster, 1975, p. 503)

REPLICAS:  So-called sculptures have been fashioned so they closely resemble coral;  at least some of them, however, are not sculptures, as the term is usually used -- they have been formed as casts in molds made  from coral.  Fortunately, these replicas -- at least all of them I have seen -- are marketed as faux red coral.  In addition, several of the above materials used to simulate coral are frequently used in the production of decorative pieces that I believe should be characterized as replicas rather than simulants.  Frames for mirrors with coral reef motifs, consisting largely of resin replicas of diverse corals are examples.  In addition, I recently saw an attractive life-sized coral-like mass made of glass that is said to include "a pinch of ash from the 1980 eruption of Mount St. Helens."

It also seems noteworthy here that jellyfish, another member of the Phylum Cnidaria, have inspired the production of some extremely attractive paperweights that feature colorful generalized replicas of these animals "floating" within clear glass. .  

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* July 4, 2006:  When the entries for this web site were nearly complete (in the hands of editors), my attention was directed to the book by Pedersen (2004).  I had not seen the book.  Upon getting a copy, as a consequence of my interest in coral, which date back to my days on Kwajalein during World War II,  I scanned Ms. Pedersen's treatment of coral and made four decisions:  1. to discontinue my efforts so far as compiling information in addition to that I had already written up about corals -- instead, to direct attention to her treatment (op.  cit., p.192-219), which is done here;  2a. to leave the material I had previously prepared on this web site, b.to add  photographs I had already solicited but not yet received, and c.to add to this entry information subsequently learned from sources other than Ms. Pedersen's book;   3. NOT  to read any more of her book until after the material I had compiled was complete (post editing stage) and on-line; [and,] 4) in the future, as I update the coverage given on this web site, to use only sources other than her fine book.

* June 4, 2009:  Special attention is directed to the following article: 
Karampelas, Stafanos,  Emmanuel Fritsch, Benjamin Rondeau, Aude Andouche, and Bernard Métivier.  2009. Identification of the endangered pink-to-red Stylaster corals by Raman spectroscopy.  Gems & Gemology.  45:48-52.

* November 6, 2010:   McClure, Kane and Sturman(2010) cite an article which I have NOT seen -- i.e.,  Weldon, R. 2003. Beryllium diffusion & disclosure. Professional Jeweler.  6(no.3):32 -- in which it is said that black coral has been bleached to a "golden coral"  but can be identified as such because of its characteristic structure.     : 

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