Lets Talk Gemstones

By Edna B. Anthony, Gemologist
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BERYL

A CYCLOSILICATE
The varieties of beryl found worldwide include one of the most prized and one of the lesser valued of gemstones. The now exhausted mines south of Koseir in Egypt provided Cleopatra with precious emeralds, including, reportedly, one engraved with her portrait. Goshen, Massachusetts is a source of the little known and relatively inexpensive namesake, the colorless "white" or "lucid" beryl called goshenite. Aquamarine, heliodor, morganite, and the color designated varieties of beryl, that include yellow, golden, yellow-green, green, and red beryl (bixbite) compose the other members of this group.

As in all the cyclosilicates, the one to three ratio of silicon to oxygen is present in the linked SiO 4 tetrahedra. Beryl is composed of stacked rings of Si 6 O 18 connected horizontally and vertically by beryllium and aluminum ions. The channels of the stacked rings can contain various ions, atoms, or molecules, including sodium, potassium, cesium, rubidium, helium, iron, hydroxyl, and water. Beryllium, first separated from beryl in 1798 by the French chemist, N.L.Vauquelin, can represent up to fourteen percent of the chemical composition of pure beryl. Thus, beryl is the prime source of this light-weight metal often used in the production of alloys. Beryl greatly increases the hardness, tensile strength, and fatigue resistance of copper.

Beryl crystals commonly develop as elongated hexagonal prisms or columns in granitic rocks and pegmatites. Thick tabular crystals are found less frequently, and pyramidal forms are rare. Crystal size varies dramatically. Finds of large nodules in alluvial debris of weathered parent rock attest to the extraordinary chemical resistance, hardness, and poor cleavage of material developed in pegmatites and the surrounding rock outcrops.

Crystals found in pegmatites can attain enormous proportions. According to the Manual of Mineralogy by Cornelis Klein and Cornelius S. Hurlbut, Jr. after J.D. Dana, a twenty-five ton, twenty-seven foot long tapered crystal of common. beryl was found in Albany, Maine. In his book, How to Know the Minerals and Rocks, Richard M. Pearl mentions another eighteen-ton find there and a forty-ton giant unearthed in Madagascar. "Well formed crystals of huge size (up to 200 tons) are common," is a direct quote from A Guide to Field Identification of Rocks and Minerals by Charles A. Sorrell, published by Golden Press.

In rock outcrops that surround the pegmatites, beryl is produced by metasomatic processes. The minerals present are replaced during the pneumatolytic phase of mineralization when the forcibly-introduced gaseous fluid solutions react chemically with the existing rock to form new minerals. Although gem quality crystals of green beryl and aquamarine that weigh as much as two hundred forty three pounds have occurred in Brazil, most gemmy crystals are much smaller.

Deposits in mica schists and calcite veins, which develop by hydrothermal processes, differ in some properties and are limited in size. The fragile-famed emeralds from Columbia grew in this manner inside calcite veins within dark bituminous limestone formations precipitating from solutions formed at lower temperatures.

Gem beryl can be confused with a number of other materials because beryl contains many colors. Beryl also exhibits the rare, but known, characteristics of chatoyancy and asterism. In 1950, a unique deposit of pale green aquamarine was discovered in the Governador Valadares region of Minas Gerais, Brazil. Crystals from this source are so intergrown with ilminite inclusions oriented parallel to the base that they exhibit a bronze luster and show a weak golden asterism. Enough variance exists in the optical and physical properties of the beryl varieties that positive identification of some specimens requires very careful gemological examination. Scratch tests to determine hardness of gemstones are seldom used. For the gemologist who lacks a more precise method than the usual heavy liquids to determine specific gravity, the location of the interference figures to differentiate the uniaxial beryl from the biaxial amblygonite can be of the utmost importance. Meanwhile, the uniaxial scapolite can pose an even greater challenge. (More on this will be discussed in a later article.)

The abundance of beryl has limited the commercial production of synthetics and imitations to the more valuable emerald, aquamarine, and red beryl varieties. The plethora of information about beryl warrants presenting it in separate articles limited to data pertinent to specific or a small number of the varieties. The first of these articles will feature the rare and unique red beryl.

RED BERYL

A CYCLOSILICATE
The discovery of red beryl crystals (bixbite) in volcanic rhyolite in the Wah Wah Mountains of Utah created a stir in mineralogical circles during the late 1970s. These white effusive igneous formations, found there and in the Thomas Mountains of Utah, and also in the tin districts of Catron and Sierra Counties within New Mexico, are still the only known source of bixbite. The same formations contain opaque bixbyite, an unrelated manganese-iron oxide, which causes confusion between the two minerals. It is noteworthy that Walter Schumann states in Gemstones of the World that scientists do not accept bixbite as a separate variety of beryl. However, no explanation for this conclusion is presented. Dr. Joel Arem states that the name bixbite honors Maynard Bixby of Utah.

The small bixbite crystals, none over two inches in length, seldom yield material suitable for cutting gems larger than one carat, although some two or three carat stones may exist. Nearly all the crystals contain numerous internal cracks, partially healed fractures, tiny bixbyite and quartz crystals, two-phase inclusions, and growth banding. Damage can be inflicted easily because of its brittle nature. In Gemstones (an Eyewitness Handbook), Cally Hall indicates that the refractive indices for bixbite, like morganite and goshenite, are relatively high for beryl. Also, red beryl, heliodor, goshenite, and morganite all show greater specific gravity characteristics than those commonly exhibited by either emerald or aquamarine.

The best color for bixbite is a clear, rich red with some blue tones. John Sinkankas attributes the red color to the oxides of manganese and cesium. According to Dr. Joel Arem in his Color Encyclopedia of Gemstones, the chemical make-up of bixbite also includes boron, lithium, lead, niobium, rubidium, tin, titanium, zinc, zirconium, "and traces of other elements".

Early efforts to capitalize upon the uniqueness and rarity of red beryl led to the practice of labeling it in the commercial gem market as "red emerald". Even today, bixbite is marketed as such. These misnomers, including "pink emerald" for morganite, only serve to misinform and further confuse the buying public. Such tactics are the bane of reputable members of the gem and jewelry industry who strive to serve the public and their clients.

The fragility, small size, and extreme rarity of bixbite precludes its use in items of jewelry except by avid collectors. Crystal specimens of any size are prized items in anyone's collection. (Editor: Although I have seen a very fine faceted red beryl set into an 18 Kt. gold ring, a pin or a pendant would have presented less risk of damage.)

SYNTHETIC RED BERYL

Previous Let's Talk Gemstones articles have focused upon properties and data pertaining to natural gemstones. Red beryl is the newest and, probably, the least known gem to be offered. Perhaps, the rapid creation and marketing of synthetic red beryl will increase the importance of presenting information regarding man-made counterparts and simulants together with information about the natural gems.
A simulant or imitation is any natural or man-made substance used to represent the gemstone which it resembles. Paste (glass) is an excellent simulant for many gems. Unlike a simulant, a synthetic gem possesses, within narrow limits, the same chemical composition, physical, and optical properties of its natural counterpart.

Recently, I was made aware of a particular source of synthetic red beryl available in both rough and faceted gemstones. WINTRA Created Emeralds, Inc. of Rockville, Maryland imports the material from Russia. I phoned the president of WINTRA, Dr. Anatoly G. Klimenko, and was able to obtain two faceted specimens. He was also kind enough to send with the specimens the gemological data that appears at the end of this article.

During our very interesting discussion, he imparted the information that synthetic bixbite is created by the hydrothermal process. This method uses water combined with an acidic mineralizer in a vessel capable of withstanding extreme heat and pressures for long periods of time. Aluminum and beryllium hydroxides used as nutrients are placed at the bottom of the container. Seed crystals of beryl are suspended in the center of the autoclave with nutrient-crushed quartz crystals positioned above them. The temperature and pressure are raised to cause the dissolution of the nutrients. Convection causes the diffused regents to form beryl in solution at the center of the container. Crystals of beryl then grow on the seed crystals. If the concentration of the solution becomes excessive, undesirable phenacite crystals, instead of beryl, develop. A highly acidic solution is necessary in the manufacture of emerald to prevent the precipitation of the added chrome, the colorant, from the solution.

Dr. Klimenko also told me that he has available the synthetic red beryl crystals grown on slices of natural goshenite, which form very unusual red and colorless layered multi-colored specimens. These could be similar to the Lechleitner product marketed about 1960, where a thin layer of synthetic emerald was grown by the hydrothermal process upon faceted examples of natural beryl gemstones.

My excitement about receiving the specimens grew as I began the examination. One stone is a well-cut 1.66 carat 8.0 x 8.0 x 5.1 mm. faceted bluish-red heart shape. The second is a 1.69 carat 8.0 x 6.0 x 5.0 mm. emerald-cut faceted gem of very similar color. The girdles of both stones have been polished. Their physical and optical properties conform to the data shown below. Microscopic examination revealed interiors with a definite orientation of a syrupy "scotch and water" effect, similar to that exhibited by hessonite garnets. In some views, the heart-shaped stone exhibited bright, sharp parallel projections at about sixty degrees, which marked the planes between distinct layers. The interior of the emerald-cut stone exhibited a slightly more "roiled" appearance with softened edges of the projections, presenting a picture of sleek tiny fish swimming in formation in a ruby sea. A plane of "frost" floated from side to side just beneath the table across one end. A transparent and highly reflective irregular rectangle with a torn upturned side gleamed from a corner at the opposite end. Dr. Klimenko doubts that it is part of a seed plate. Perhaps, further information regarding this unusual inclusion may be available from the manufacturer at a future date.

{Anyone wishing to reprint this article by Edna Anthony must obtain permission from the author.}

The following gemological data has been obtained from Dr. Anatoly G. Klimenko, President of WINTRA Created Emeralds, Inc. Dr. Klimenko may be reached by telephone at 1-301-340-9258 and by fax at 1-301-340-8222. The address for WINTRA Created Emeralds, Inc. is: 1783 Redgate Farms Court; Rockville, Maryland 20850.

* No information specifics were available concerning the spectral norms, nor for reactions to the Chelsea and Aqua Filters. Thermal traits for the synthetic red beryl material were presumed to be similar, if not identical, to natural red beryl. The inclusions discussed in the article were specific to the two specimens of synthetic red beryl that I had available for examination.
 
Gemstone Properties
SPECIE
WINTRA Created Red Beryl
Chemical Composition
Al 2 [Be 3 (Si 6 O 18 )] (R,H 2 O)<1.5
Crystal System
hexagonal
Habit
prismatic
Specific Gravity
2.69 to 2.70
Hardness
7.5 to 8.0
Toughness
fair
Cleavage
very difficult and very brittle
Fracture
not specified; natural red beryl exhibits conchoidal fractures
Fracture Lustre
vitreous to resinous
Diaphaneity
transparent to translucent
Lustre
vitreous
Refractive Index
0 = 1.5685 and e = 1.579
Birefringence
0.006
Optic Character
uniaxial and negative
Pleochroism
purplish red and orange red
Dispersion
0.014
Ultraviolet Fluorescence
inert
X-ray Fluorescence
not given
Transparent to X-rays
opaque
Acid Resistance
resistance to all except hydrofluoric 


 
Gemstone Properties
SPECIE
Bixbite
Composition:
beryllium aluminum silicate
Al 2 Be 3( Si 6 O 18 ) + Mn, Cs, Ti, Pb, Li, B, Sn, Rb, Nb, Zn, Zr
Class:
cyclosilicate
Group
beryl
Species:
red beryl or bixbite
Crystal System:
hexagonal
Varieties:
bixbite
Colors:
red and violet red
Phenomena:
none known
Streak:
white
Diaphaneity:
transparent and translucent
Habit:
small elongated prisms 
Cleavage:
indistinct
Fracture:
conchoidal
Fracture Lustre:
vitreous to resinous
Lustre:
vitreous
Specific Gravity
per Joel Arem: 2.66 to 2.70
per Cally Hall: 2.80
Hardness
7.5 to 8
Toughness:
fragile; the numerous inclusions can influence fracture
Refractive Index
per Joel Arem: 0 = 1.568 to 1.572 and e = 1.567 to 1.568
per Cally Hall: 0 = 1.59 and e = 1.58
Birefringence:
per Joel Arem: 0.004 to 0.008
per Cally Hall: 0.008
Optic Character
uniaxial negative
Dispersion:
0.014
Pleochroism
the specimens in my personal collection show weak shades of red
Ultraviolet 
Fluorescence
the specimens in my personal collection show none
Spectra
none discernible in the specimens from my personal collection
Color Filter
Aqua Filter
the crystals in my personal collection almost fluoresce; the faceted specimen shows no change
Chelsea Filter
no reaction in the specimens from my personal collection
Solubility
HF in concentrate can etch other beryl; no specifics for red beryl
Thermal Traits
avoid thermal shock; beryl fuses into bubbly glass
Treatments
none known
Inclusions
partially healed internal fractures with quartz and bixbyite