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On "Odontolite" or "Bone Turquoise"

Last Updated: 19th Jan 2008

Some (Incomplete) Notes On
“Odontolite” or “Bone Turquoise”



Introduction

“Odontolite” is a turquoise simulant derived from fossil bones, most commonly the teeth of mastodon and other large species of mammals.

The turquoise-blue color of odontolite has been ascribed to several causes, including impregnation of the bone by traces of copper and by the development of vivianite (an iron phosphate) in the bone. Recent research, however, has disproved many of these earlier notions.

Synonyms

Synonyms that have been applied to Odontolite include “occidental turquoise” (as opposed to “oriental turquoise,” the mineral turquoise); “bone turquoise”; “fossil turquoise”; “mammoth turquoise”; “ivory turquoise”; “French turquoise”; “fossil toothstone”; “Zahnturkis”; and “turquoise de la nouvelle roche” (“turquoise of the new rock” as opposed to “turquoise of the old rock”, i.e., the mineral turquoise).

History

In 1819, Russian naturalist Johann Gotthelf Fischer von Waldheim summarized the quandary:
”The term turquoise has been applied to two very different substances. The one, distinguished by the name of oriental turquoise, is a true stone, a clay coloured by oxide of copper, or even by arseniate of iron; and belongs as much to the argillaceous order of the oryctognostic system as chrysoprase belongs to the siliceous order. I have placed it in the system under the name of calaite, by which it had been already distinguished by Pliny. The other substance, called simply turquoise, or occidental turquoise, or turquoise odontolite, is a fossil, a petrefaction, a tooth or a bone coloured by a metallic phosphate, which does not belong to the mineral kingdom at all. Every part of the skeleton may be in this way converted into turquoise, when it happens to be placed in contact with coppery bodies, and particularly with phosphate of copper; but the fossil turquoise capable of being employed in the arts is almost always a tooth, which is harder than the other bones of the skeleton, and takes an excellent polish. I shall distinguish it by the name turquoise odontolite…”
Some scholars have suggested that the earliest reference of odontolite as a gem material dates back as far as Theophastus (ca. 350BC), who mentions “fossil ivory which is variegated with white and dark markings.” John Hill, in his notes to his 1774 translation of Theophrastus’ “On Stones”, asserted that Theophrastus’ choice of term “dark” (”melani”) did not necessarily mean “black” and, since he immediately thereafter applies the same term to sapphire, should be taken as “dark blue”. Calley and Richards (1956) point out that “Some later authors… have accepted this suggestion and have attempted to improve upon it by proposing that the material in question was not true turquoise, which is often light blue or green, but false turquoise or odontolite, which consists of fossil bones colored blue by vivianite, a hydrated iron phosphate. However, since all these identifications are based on the assumption that the material which Theophrastus calls fossil ivory was partly blue in color, they must be considered as little better than conjectures.”

One of the earliest detailed descriptions of odontolite was set to paper in 1628 by Guy la Brosse. Physician to the king of France and an eminent botanist who founded the famed Jardin des Plantes in Paris, la Brosse realized that odontolite (which he called “licorne minerale” and “mother of turquoise”) was not genuine turquoise. The material "is a stone having the shape of a horn, and the consistence of a stone, which, being exposed to a graduated heat, gives the true turquoise. It is called licorne minerale because it resembles the horn of an animal.” (Fischer, 1819) [Emphasis is mine].

In 1715, French scientist Rene Antoine Ferchault Reaumur published “Observations sur les Mines des Turquoise du Royaume sur la Nature et la Maniere dont on lui donne la Couleur.” Reaumur was a scientific jack-of-all-trades, publishing works on such widely-ranging subjects as animal behavior, starfish, thermometry, making iron and steel, silk-making, and entomology. He invented the cupola furnace, one of the early forms of blast furnace.

According to Fischer, Reaumur documented two mastodon teeth being used for odontolite, and detailed “the manner of heating the turquoise, and gives a figure of the peculiar furnace employed for the purpose. From this, what I stated above follows clearly; that the French turquoises are prepared by the fire, and consequently are partly artificial.”

Fischer listed the main ways of differentiating real (mineral) turquoise from odontolite. Turquoise was harder than odontolite. The specific gravity of odontolite was higher that true turquoise (3.127 g/cm3 vs 2.6 to 2.8 g/cm3 for “real” turquoise.) Distilled vinegar (acetic acid) decolorized odontolite, and nitric acid dissolved it. When heated, odontolite released a noxious odor. And, “the polish of [odontolite] is not so good as that of the [true turquoise], and exhibits plates, rays, or filaments, depending upon the bony structure. Rosnel affirms with justice that all the turquoises of France have their surface covered with radii, or filaments. And… Reaumur affirms that the more sensible the plates are, the worse are the turquoises…” The “plates, rays and filaments” of course refer to the fairly well preserved bone structure evident in odontolite. Lastly, odontolite did not melt in the flame of the blowpipe, but instead turned grey. . Before the blow-pipe it became greyish-white without melting. “This operation rendered it friable, and it lost 0.06 of its weight.”

He cites an analysis of odontolite by French chemist Edme-Jean Baptiste Bouillon-Lagrange, which fails to detect the presence of either copper or aluminum:

Composition of Odontolite

Phosphate of lime80%
Carbonate of lime8%
Phosphate of iron2%
Phosphate of magnesia2%
Total92%

“The French jewellers consider it as a principle, that the true turquoise should effervesce in sulphuric acid. This is a proof that they think only of the French turquoise, or turquoise odontolite, the true stone, or calaite, not yielding to the strongest acids.” he adds. [emphasis mine]


Fischer’s Odontolite Teeth
Fischer then takes up the question of what parts of fossilized animals provide odontolite:

If we give the name of turquoise to every animal substance which has been penetrated and coloured green or blue by metallic oxides, and particularly by copper, it is obvious that any part of the skeleton, and even the whole body, may have been converted into turquoise provided all the parts be capable of undergoing the change. But it appears that the teeth are the only parts which possess sufficient hardness to become true turquoises in the full acceptation of the word. If entire skeletons, or parts of skeletons, still surrounded with dried muscles, have appeared to assume the form of turquoise, it seems more reasonable to consider them as passages to that state than as true turquoises.


As a good biologist, Fischer then goes on to provide painfully detailed descriptions of teeth of known and unknown mammals which have provided bone turquoise or were similarly mineralized. Of one tooth he examined, he comments “it was completely penetrated with the green colour, so that it had the appearance of being composed of malachite. This tooth was given to our Society by M. Nikite de Mouraview, but it was unfortunately destroyed in 1812 by the flames… I have seen some of them green, some azure blue, and others only partially coloured…” (The flames which Fischer speaks of was, of course, the Burning of Moscow was Napolean’s troops marched into the city in 1812)

Describing a tooth formerly in his collection – also lost in the Burning of Moscow – he notes “there is a similar one of a very deep-green colour in the rich museum of the Imperial Academy of Sciences of St. Petersburgh. One of my pupils gave me a third of the same animal, but it has only a slight tinge of azure blue.” I likewise lost this tooth by the flames, I have reason to believe that these teeth come from Miask, in Siberia.” The “Miask” of which he speaks is probably an alluvial gold deposit. Mining engineer William P Blake stated “at the Soimanofsk mines, north of Miask, there are placer deposits of gold upon the rough decomposed surface of limestone…where… the remains of the mammoth and the mastodon are found in the gravel with the gold.” (Blake, 1869)

Fischer also noted a tooth that was “found in a copper mine in the government of Olonez, which has been abandoned these 20 years… It is entirely covered with a verdigris-coloured oxide of copper.” (Today it is known as Olonetz, was a small city in the southern Karelian Republic in Russia.)

Localities Which Produced Odontolite

The most localities producing odontolite for commercial purposes were in France, especially in the Gers district. “They occur in Lower Languedoc, near the town of Simore and its environs, as at Baillabatz and at Laymont. There are others, according to Reaumur, nearly in the same country, on the side of Auch, at Gimont, and at Castres.”

An anonymous author stated in 1878 “the bone or fossil turquoise (odontolite) found in Languedoc is sometimes called turquoise-Bricaud, from the name of the original owner of the mine.” (Anon. 1878) No further information of "Bricaud" and his involvement in odontolite mining has been uncovered.

To this list, Fischer adds “other depots are likewise mentioned, from which I have not yet seen specimens ; namely, Nivernois, Silesia, Lesta in Bohemia, Thurgau in Switzerland. We must add likewise from my observations, Siberia (Miask), and the government of Olouez. The number of places will doubtless augment in proportion as more attention is paid to fossils.”

Causes of Color in Odontolite

The cause of the blue color in odontolite remained a subject of debate for more than 180 years. Having ruled out copper as the cause through simple chemical tests, it was suggested that iron phosphate (vivianite) was the colorant. Certainly, much of the fossil bone buried in the soils of France and Siberia would show trace amounts of iron, and since bone was largely composed of an apatite-group mineral it would demonstrate phosphorus.

By the late 19th Century the “vivianite theory” became gospel throughout the mineralogical and gemological communities. “The bone turquois, or odontolite, on the other hand, is merely bone or ivory coloured sky-blue or bluish-green by phosphate of iron…” (Page, 1874). Streeter (1892) states “this fossil Turquoise derives its blue colour from the phosphate of iron, or Vivianite, with which it is impregnated.”

It was not until 2001 that the issue of the cause of color in odontolite was revisited. Reiche et alia undertook a study of odontolite gems used as adornment on a 13th Century religious artifact produced in Limouges, France. As anticipated, no copper was observed. However, they also failed to identify any vivianite in the odontolite they studied. While trace amounts of iron were present, the hoary hypothesis that odontolite owned its color to vivianite was shown to be invalid.

Instead of vivianite, odontolite was predominantly composed of fluorapatite containing trace amounts of iron, manganese, uranium, barium, lead and rare earth elements. They determined that the predominant coloring agent was manganese in the Mn5+ valence state as an integral part of the fluorapatite structure. They also observed that the crystallites of fluorapatite were about 10 times larger than that of unheated mastodon ivory as the result of being heated to a temperature of approximately 600° C, further validating the observations of la Brosse and Reaumur.





Bibliography

• Anonymous “Precious Stones” The British Quarterly Review. January And April, 1878. Vol. 67. New York 1878.

• Blake, William P., Production Of The Precious Metals: Statistical Notices Of The
Principal Gold And Silver Producing Regions Of The World. New York: E P. Putnam & Son. 1869.

• Calley, Earle R and Richards, John F C Theophrastus on Stones, Ohio State University,1956

• Duncan, Jonathan “Reaumur” The Guernsey and Jersey Magazine Vol. 2, pp 141 (1836)

• Fischer, Gotthelf “Essay on the Turquoise and the Calaite” Annals Of Philosophy Thomas Thomson, editor. Vol. 14, pp. 406-420 1819.

• Page, David (1874) Economic Geology Or Geology In Its Relations To The Arts And Manufactures London

• King, R. J. (2002) Turquoise Geology Today 18 (3), 110–114.

• Reaumur, René Antoine Ferchault “Observations sur les Mines des Turquoise du Royaume sur la Nature et la Maniere dont on lui donne la Couleur” Mem. de 1'Acad. des Sciences de Paris, 1715. pp 174—202

• Reiche, Ina, Colette Vignaud, Bernard Champagnon, Gérard Panczer, Christian Brouder, Guillaume Morin, Vicente Armando Solé, Laurent Charlet and Michel Menu (2001) “From mastodon ivory to gemstone: The origin of turquoise color in odontolite” American Mineralogist; November 2001; v. 86; no. 11-12; p. 1519-1524

• Streeter, Edwin R. (1892) Precious Stones And Gems, Their History. Sources And Characteristics. Fifth Ed London 1892





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