THE GOLD OF THAT LAND: Biblical Minerals & Rocks  


 

14.     carbuncle

Hebrew:

    1. nôphek, derived from the word for lightning to describe a fiery gemstone. Exodus 28:18; 39:11, Ezekiel 27:16, 28:13.

    2. 'ekdâch, a gemstone glowing with fire. Isaiah 54:12

Greek: anthrax

Probable Identification: a red garnet: either pyrope  or almandine.

Mineralogy:

    A carbuncle in modern usage is a deep red almandine garnet with a cabochon cut. Garnets are a group of isometric aluminosilicate minerals that typically form distinctive dodecahedral (12 faces) or trapezohedral (24 faces) crystals in metamorphic rocks and rarely in granite. Our word garnet comes from the Latin granatum because small red garnets superficially resemble pomegranate seeds. Carbuncle derives from the German word Karfunkel. The hardness and specific gravity of garnets vary with composition from 6.5 to 8 and 3.4 to 4.3, respectively. The red, iron rich garnets have the highest hardness, density and brilliance.

    The six principal species of garnet include almandine, pyrope, spessartite, grossularite, andradite, and uvarovite. At least twenty rarer species form by substitution of trace elements. Pyrope, spessartite, and uvarovite have semi-precious varieties, and deep red transparent pyrope [Mg3Al2(SiO4)3] is a likely identification for Isaiah 54:12.

    Almandine [Fe3Al2(SiO4)3], a common red garnet, characteristically occurs in mica schist with quartz, staurolite, and feldspars. Large almandine crystals are relatively common. The name comes from Alabanda, an ancient gem-cutting center in Asia Minor, and almandine varies in color from deep red to nearly black.

    Pyrope's Greek and Arabic names mean fiery-eyed. Large pyrope crystals are much rarer than large almandines. Bohemia produced fashionable deep red pyropes of high quality until they were mined out in 1910.  Gem spessartine from Ramona, California is a rich orange. Demantoid, the "Siberian emerald," is an emerald-green to yellowish-green gem variety of andradite from the Ural Mountains that rivals emerald in value. Demantoid also occurs in China, Korea, the United States, and Zaire. Tsavorite from East Africa surpasses emerald in the intensity of its green and all other properties except size of stones.

Historical Background:

    A Talmudic legend says that a huge fiery red garnet illuminated the interior of Noah's ark like a lantern.

    The Egyptians mined almandine at Aswan, Kharga Oasis, in the eastern desert, and in Sinai. The largest stones came from Aswan and western Sinai. They made beads from dark red or reddish brown translucent almandine as early as predynastic times. A diadem from Abydos, dated at 3200 BC, consists of almandine, malachite and turquoise beads separated by gold beads. The Egyptians later inlaid almandines in the eyes of statuettes. The opening of a supply of garnets from India by Alexander the Great made them popular as intaglios for seal rings in Hellenistic and Roman times. The carvers of Greek intaglios perfected the craft of raising rather than incising their intricate designs.

    As the most common garnet and the first used in jewelry, almandine's superior chemical and physical properties make it tough and resistant to abrasion. Modern industry uses almandine in garnet abrasives, water filters, special cements, and radiation shielding. The 1997 world production of industrial garnet exceeded 140 million metric tons. Most almandine today comes from alluvial deposits in the Jaipur area of India. Other sources are Brazil, Burma, Ceylon, and the United States.

    Geologist John Gurney accelerated today’s hunt for new diamond pipes by determining that G10 garnet, a purple variety of pyrope rich in chromium but low in calcium content, is a reliable indicator of prospective diamond-bearing pipes because it forms deep in the earth’s crust under the same conditions of heat and pressure.

 

Note:

Contrary to A. Conan Doyle's Sherlock Holmes story "The Adventure of the Blue Carbuncle," blue carbuncles were unknown in Doyle’s time. Perhaps Doyle meant a sapphire with a carbuncle cut. This cut gives a stone a cabochon (convex) face and concave back to reduce its thickness and heighten the brilliance of its internal reflections. Although it brings out the fire of large dark almandine and pyrope stones, a carbuncle cut would be unnecessary for a blue sapphire. The mystery continued until the recent discovery in Madagascar of a blue variety of grossularite resembling tsavorite (or tsavolite). Tsavorite, discovered in Tanzania in 1967 and Kenya in 1971, owes its intense deep emerald green to yellow green color to traces of chromium and vanadium. The Madagascar specimens are blue with a greenish cast, and contain vanadium but no chromium. The absence of chromium qualifies them for a new name and may account for their blue color.

 

Sources:

Hart, Matthew, 2001. Diamond: a journey to the heart of an obsession. New York: Walker & Co.; 27-29.

Hernandez, Rosario Lunar, Jesus Martinez-Frias, Raul Benito, & Dieter Wolf, 1999. Nijar and the garnets of Europe. Geotimes: 44-1, 22-27.

Hodgkinson, Alan, 1980. Blue garnet. http://www.scotgem.demon.co.uk/bluegarnet.html

Hurlbut, 1952, op. cit.; 382-387.

International Colored Gemstone Association, 2002. Tsavorite. http://www.gemstone.org/gem-by-gem/english/tsavorite.html

Lucas & Harris, op. cit.; 394-395.

Ralph, Jolyon, 1993-2004. http://www.mindat.org/min-3321.html & http://www.mindat.org/min-min-452.html

Rouse, John D., 1986. Garnet. London: Butterworths.

Schumann, op. cit.; 104-107.


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