( Fr- chalcédoine; Ger- Chalzedon; Nor- kalsedon; Rus- )
CHALCEDONY, SiO2. (See also AGATE, CHERT, "CHRYSOCOLLA," JASPER, ONYX and THUNDER EGG entries.)
A. Bloodstone was thought to have the virtue of healing diverse blood-related maladies. This old woodcut depicts its use in quelling a nose-bleed. (from Hortus Sanitatis by Cuba, ca. 1483)
B. Chrysoprase rough (height - 4 cm) from Marlborough, Queensland, Australia. Gene Meieran collection. (© photo by Jeffrey A. Scovil)
C. Chrysoprase cabochon (greatest dimension - 4 cm) from Marlborough, Queensland, Australia. (© photo by Jeffrey A. Scovil)
D. Carnelian engraved stone (greatest dimension - 2.3 cm). Peter Secrest Collection. (© photo by Jeffrey A. Scovil)
E. Blue chalcedony (rough piece, height - 5.5 cm) from Namibia (formerly South West Africa). Sunlight Gems. (© photo by Jeffrey A. Scovil)
F. Bloodstone. (rough piece, height -
6.5 cm) from unknown locality. Ariel collection. (© photo by
Jeffrey A. Scovil)
DESCRIPTION: Chalcedony is micro- or
quartz that, strictly speaking, includes agate and onyx,
which are treated in separate entries in this document (q.v.). In addition, several
other varieties of chalcedony have names that are used widely in
gemology and by lapidaries; these are the names given in
underlined, upper case letters in the first list under the OTHER NAMES
subheading. Another aspect of describing chalcedony relates to
the fact that distinguishing
certain varieties of chalcedony -- especially those that are
subtranslucent or opaque -- from certain jaspers and chert is
subjective; indeed such distinctions are frequently based on the
experiences of the person naming them (see CHERT and JASPER entries).
Colors - white, gray, black, brown, reddish, orangy, yellow, light to dark green, bluish, violet or combinations of those colors -- e.g., "purplish blue and red-brown (Hyršl, 2011)
H. 6 -7
S.G. 2.6 + 0.5
Light transmission - transparent to virtually opaque with most varieties translucent
Luster - waxy to dull luster
Breakage - subconchoidal fracture yielding fine granular appearing surfaces
Miscellaneous - commonly triboluminescent.
OTHER NAMES: Some chalcedonies with characteristic colors occur rather widely and have had a long history of use as gemrocks. Consequently, they have been given names that are applied widely by both professionals and laymen. The names of these rather common color varieties follow:
Almost innumerable additional names have also been given -- for the most part in the marketplace -- to other gemrocks made up wholly or largely of chalcedony. These names range from usefully descriptive -- e.g., blue chalcedony -- to fanciful -- e.g., Saint Stephen's stone. Many examples of such additional names, which are seen only too frequently in rock shops and advertisements, are treated in several publications -- see, for example, Hart (1927) and the "Dictionary of Gems and Gemology" (GIA, 1974). A few examples follow:
USES: Chalcedony was used to make
cylindrical seals in Mesopotamia as early as the 7th century
B.C. Subsequently, it has been used widely for fashioning
stones for jewelry, buttons,
carvings -- including cameos and intaglios
utilizing banded varieties such as agate, onyx, and sardonyx and even
chalcedony enhydros (i.e.,
calcedony that contains free water within cavities) -- and virtually
all the other uses for which gemrocks have been utilized. One
especially interesting one is its use as the backing for assembled
gemstones. Also, it is one
of only a few gemrocks that has been fashioned into hololiths. An
especially noteworthy use is its incorporation, along with other
gemrocks such as lapis lazuli, malachite, and rhodochrosite in intarsia
(gemstone inlay) pieces. In addition, it is commonly dyed and
marketed as simulants for other gemstones -- e.g., black to resemble
A description and photographs of clams that have been replaced, some of them largely, by carnelian would seem likely to lead to their becoming widely sought for use as decorative objects. They are from the Petrified Forest area, Apache County, Arizona. (Bain, 2012)
OCCURRENCES: Commonly as botryoidal crusts on or completely filling preexisting cavities such as vesicles and fissures in volcanic rocks and other rocks including breccias.
NOTEWORTHY LOCALITIES: See localities given under terms listed under the OTHER NAMES sub-heading. Also:
Bloodstone - Probably the best known bloodstone has come from the Deccan traps of the Kathiawar Peninsula, India. Kraus (1976) also lists the Ile of Run (Isle of Rum of the Hebrides?), Scotland.
Carnelian - Ratnapura, Sri Lanka (formerly Ceylon); Brazil-Uruguay agate area (see AGATE entry); Fletcher River basin, Queensland, Australia; Maricopa County, Arizona; the arid area along the Colorado-Utah state line; andLewis County, Washington.
Chrysoprase - Frankenstein, Kosemütz and Gläsendorf, Poland (formerly German Silesia); near Marlborough, Queensland and at Yandramindra and near Wingelina in the Warburton Range, Western Australia; near Exeter, Lindsay and Visalia, Tulare County, California; and near Riddle, Oregon. (Also noteworthy is a chrysocolla-containing chalcedony, which resembles chrysoprase, that is recovered from copper mines in the Globe mining district of Gila County, Arizona.)
- Durkee, Baker County, Oregon; and Clarke County, Washington.
Prase - Bucks, Delaware and Chester counties, Pennsylvania.
REMARKS: Application of the
designation chalcedony to this variety of quartz dates back at least to
Bible times -- see Revelation, XXI:19, where it is given as "the name
of the precious stone forming the third foundation of New Jerusalem,
but found nowhere else ... The word is of very complicated history."
(OED, 1989 ed.) Nonetheless, it seems that Its derivation may
relate to the material's coming from or being marketed
at or through Chalcedon (Khalkēdōn), currently Kadiköi
(Kadi-Keui), a suburb of Istanbul (formerly Constantinople), on
the Asiatic side of the Bosporus, Turkey.
Origins and/or derivations of some of the terms applied to
well-recognized varieties of chalcedony follow:
Carnelian (Cornelian) -- apparently
based on its color -- i.e., likely from the Latin
carnem meaning fleshy(colored);
alternative: "perhaps from Medieval Latin name cornus for a species of dogwood
with a reddish berry." .
Chrysoprase -- apparently
based on its color -- i.e., from
the Greek χρυσόπρασος (= χρυσός [gold(en)] and πρασον [(color of) leek]); and thence to Latin chrysoprasus; Old French, crisopras; and Middle
Plasma -- Mitchell(1979) suggests " from Greek plasma [πλασμα], used for things formed or molded, probably applied because
the mineral was used for intaglios."
Prase -- apparently based on its color -- i.e., from Greek πρασον (~color
of leeks) ... etc. -- see Chrysoprase,
Sard -- from
Latin sarda, possibly from Sardes, an
ancient city that was in today's eastern Turkey -- i.e., in the Gediz (formerly
Hermus) River valley, about 80 km east of Izmir (formerly Smyrna),
which is a seaport on the Aegean Sea -- perhaps as a result of its
availability there, as mentioned for chalcedony and Chalcedon.
Chalcedony is typically porous, so light colored chalcedony, in particular, can be dyed just about any color. Consequently, chalcedony has been dyed to resemble other gemrocks -- e.g., lapis lazuli -- and otherwise unmarketable chalcedony has even been dyed to the color of one of its desired varieties -- e.g., chrysoprase. Indeed, on occasion, some "off-colored" chalcedony has been bleached before dyeing it in order better to achieve the desired color. Three well known examples of dyed chalcedony are aniline-dyed red chalcedony, which is marketed as coralline; chalcedony dyed green and marketed as emeraldine; and chalcedony dyed black and marketed as a substitute for black gemstones such as jet, "onyx" and even black pearls. In addition, the color of some chalcedony has been changed by heating with the typical end product assuming a reddish hue -- e.g., "Some reddish material sold as carnelian is obtained by the heat treatment of greenish, yellowish, or brown chalcedony" (Frondel, 1962, p.207). Along this line, chrysoprase has been recorded as having faded when heated, even by the sun; however, it also has been recorded that the original color sometimes returns when the faded chrysoprase is stored in certain high humidity environments. Yet another "treatment" is the backing of thin wafers of translucent chalcedony with diverse foils to give them certain special appearances.
Liddicoat (1966-67) and Fischer (1991) describe processes used to "mossify" chalcedony to make it resemble moss agate: One of the procedures involves the use of silver nitrate; the others, not well outlined, create copper and tin dendrites within translucent chalcedony. Descriptions of some end-products of the latter processes indicate that the "induced copper dendrites in chalcedony are relatively attractive because of the color of the metal and the blue-green body color that the copper salt solution gives to the host chalcedony ... [whereas] the induced tin dendrites ... are a dull silvery gray, and the solution apparently does not produce an attractive color in the host ..." (Johnson et al. (2000, p.170-171)
A blue chalcedony containing several red so-called inclusions is described anonymously in a news item in Volume I (1935, p.196) of Gems & Gemology as "'Blue Eagle chalcedony' ... because of its natural resemblance to the blue eagle emblem of the N.R.A. ... The inclusions surround a patch of the blue background in such a manner as to form an almost perfect eagle." This item is but one of many examples, to which I have had my attention directed, that have been likened to all sorts of both real and fanciful items and beings by connoisseurs of gemrocks and other geological features called mimetoliths -- See the MIMETOLITH file on this web site.
Chalcedony has been ascribed such diverse powers as prevention and curing of melancholy and driving away evil spirits. With respect to the former, Merrrill (1922, p.158) notes that chalcedony "worn as an amulet and in contact with the hairs of an ass, ... was a preventive of danger during tempests and sinister events." Chalcedony is listed as the third precious stone of the foundations of the Heavenly City walls, in Revelation (XXI:19) of the Bible. Blue chalcedony, which typically is banded blue and off-white, is the official state gemstone of Nebraska.
Bloodstone -- in this context, more accurately heliotrope (which means sun-reflecting) -- was apparently believed by ancient Greeks to emit heat from the sun when put into water, thus causing the water to boil. Bloodstone also has been attributed several healing attributes, especially those dealing with blood (see Figure A). Another belief was that bloodstone placed on a blind person's eyelid it would restore sight. Also, legend has it that the red specks (etc.) in bloodstone developed when Christ shed blood while on the Cross. In addition, bloodstone has been interpreted by some scholars to be the 12th stone in Aaron's breastplate (see GLOSSARY), and some people consider bloodstone to be the birthstone for March while others relate it to the zodiac symbol Aries (March 21 - April 20).
Carnelian has been recommended as an aid for anyone having a weak voice or a reluctance to speak; the belief was that carrying or wearing something including carnelian would give the person courage both to speak out and to speak clearly and loudly. For whatever reason, carnelian has indeed been worn as pendants or amulets for untold centuries. In fact, Napoleon is recorded as having carried one he found in Egypt and to have had faith in it as a talisman. Perhaps he followed the belief reported by Merrill (1922, p. 158) "the wearing of carnelian insured victory in all contests save those of love." According to some scholars, carnelian, along with other chalcedony gemrocks -- i.e., onyx, sard and agate -- occupied one or another position on Aaron's and/or High priests' breastplates. Today, carnelian is considered by some people to be the birthstone for July and by others to be related to the Zodiac sign Virgo (August 22 - September 22).
Chrysoprase, considered by some people to be the most valuable variety of chalcedony, has been used as the rough material in the production of carved gemstones -- both cameos and intaglios -- since at least the days of the Roman Empire. It was frequently associated with curing disorders that today are usually associated with uric acid abnormalities -- e.g., gout and kidney stones. Chrysoprase is also one of the stones listed as in the foundation of the Heavenly City. Today, according to some schemes, chrysoprase is the birthstone for May.
Prase has been believed by some people to have all the powers of emerald, albeit to a diminished degree. Included was its purported role as a cardiac stimulant and its mixture with ewe's milk to cure gout.
Sard, or possibly sardonyx, is widely thought to have been the first stone on the first row of the High Priest's breastplate. Sard was once thought to possess sex, the male shining more brightly than the female. It also was thought to protect anyone who wore or carried it from "witchcraft and noxious humors" (Merrill, 1922, p. 175).
as recorded by Plinny (xxxvii.75 -- as
translated by King, 1865) provides an early example of gemstone
forgery: It seems that three colors once were considered to be
characteristic and that some "Sardonyx gems are made up out of three
stones cemented together so neatly that the fraud cannot be
discovered..." Although sardonyx
was long thought to be a symbol of conjugal bliss (Merrill, ibid.), history has it that a sardonyx cameo with her image
carved on it was
given by Queen Elizabeth I to the Earl of Essex but that later, because
it was found in the possession of the Countess of Nottingham, it led to
Essex's execution. Sardonyx is yet another
stone listed as in the foundation of the Heavenly City. In addition, it is considered by some to be the
for August: Although my birthdate is a half year removed from August,
the first ring I ever
had was sterling silver with a flat oval stone said to be sardonyx ; while
reviewing some of the miscellany about gemrocks, I think I have
discovered why this choice may have been made -- Kunz (1913, p.107)
believed to sharpen the wits of the wearer."
following is part of the AGATE entry: Blue agate
(I have been told, but have not
been able to confirm this, that blue chalcedony actually has this
and Prairie agate are, respectively, Nebraska's official state gem and
Citron chrysoprase - nickeloan magnesite from
Western Australia - [inferior hardness (H. ~4), higher specific gravity
(~3.0); effervesces with warm HCl].
"Hokkaido agate" - the outer portions of some
agates "from the northernmost of the Japanese Islands ... [which
is] porous, is usually dyed to resemble carnelian."
Lemon chrysoprase - a yellow-green quartz-magnesite rock made up of white quartz and green magnesite, probably containing noteworthy gaspeite molecule (Johnson and Koivula, 1996, p.217) - [Magnesite component has inferior hardness (H. 3½ -5) and effervesces with warm HCl.].
***Maple stone - an Imori glass sometimes used as
a bloodstone simulant - [vitreous luster; inferior hardness (H.
Oriental jasper - name sometimes applied to
bloodstone - [see Jasper entry.].
Serpentine - A pierced disc sold as red
chalcedony was found to be dyed antigorite, which is a variety of
serpentine (Rondeau et al., 2009) - [inferior hardness of serpentine
should suffice; also, the red color was concentrated in fractures
and the central portion of the disc was "largely colorless."].
simulants but noteworthy here is the fact that chalcedony that has been
dyed is recorded in the literature. McClure, Kane and Sturman
(2010), cite a couple examples.]
REFERENCES: Frondel, 1962.
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