The last article
on the gemstones of the beryl group closes with morganite as the subject.
I think it appropriate now to review the nature and characteristics of
the beryl group. Beryl is a mineral of a class of minerals called silicates.
Silicates are minerals composed primarily of silicon and oxygen (SiO4)
tetrahedra. The tetrahedra can remain independent (orthosilicates or nesosilicates)
or bond in various ways to form sorosilicates (two linked groups), inosilicates
(single or double chains), phyllosilicates (flat sheets), cyclosilicates
(rings) or the framework silicates known as tectosilicates. Mineralogist
Paul Hlava describes the ring structure of beryl as "an array of tires
stacked one atop the other, with sheets of beryllium and aluminum ions
between the layers." The ring structure of beryl produces six-sided prisms
of moderate density and above average hardness that frequently exhibit
numerous striations parallel to the length of the crystal.
Beryl is usually found in pegmatitic regions of granite and silica-poor
mica schists or in the alluvial debris of such eroded areas. The hardness
of beryl, its chemical resistance, and the lack of planes of definite
cleavage aid in the preservation of the crystals in alluvial environments.
Rarely does beryl occur in high temperature cavities (druses), where it
precipitates from very hot beryllium-bearing solutions or gases. Rod-like
masses are also uncommon. The crystals usually develop as elongated hexagonal
prisms. However, the alkali-rich morganite is the exception, as it frequently
occurs as short stubby crystals and in tabular form. Dr. Frederick H.
Pough has stated that "tabular beryl crystals have been found in abundance
in New Mexico at Dixon." The Pala and Mesa Grande districts of San Diego
County in California produce crystals of superb quality. Deposits in Maine
yield material associated with the tourmaline and other gem varieties
found there. The pegmatites of the island of Madagascar (Malagasy Republic),
particularly the deposits at Anjanabonoina, are the source of some very
fine crystals. In the Eyewitness Handbook series, Cally Hall in Gemstones
lists the recently discovered deposits in Pakistan, as well as the productive
areas in Mozambique, Zimbabwe, Namibia, and the island of Elba (Italy).
Illustration #18 in Crescent's Color Treasury of Crystals shows a picture
of a very well developed 9mm. morganite crystal from Elba, now on display
in the Natural History Museum of Milan.
Pure beryl is colorless goshenite. However, the channels formed by the
stacked rings, where they are parallel to the C axis, can accommodate
various ions, atoms, and molecules. Aquamarine, emerald, heliodor, green
beryl, and morganite crystals develop when the structure contains the
appropriate traces of other elements or minerals. Cally Hall mentions
bi-colored Brazilian crystals composed of aquamarine and morganite.
Vorobyevite, vorobievite, worobieffite, rosterite, and rose beryl are
terms used in earlier publications to designate pink beryl, now commonly
referred to as morganite. The noted Tiffany gemologist, Dr. George F.
Kunz, named the little known gem after the affluent New York banker and
gem collector, John Pierpont Morgan. Later, the extensive Morgan gem collection
was donated to, and now displayed at, the American Museum of Natural History
in New York.
Various authorities have named cesium, lithium, and manganese as the
color-producing agent in morganite. Dr. J. Kourimsky in The Illustrated
Encyclopedia of Minerals and Rocks attributes the color to cesium, and
Dr. Pough refers to "pink cesium beryls." Dr. Kurt Nassau states in his
Gems Made by Man, that the presence of manganese in natural beryl produces
morganite. The Illustrated Dictionary of Jewelry by Harold Newman defines
morganite as "rose-pink, owing to the presence of lithium." In Gems in
the Smithsonian, Paul Desautels also claims that lithium "accounts for
the color of pink beryl." Extensive research within the last few years
has brought such dogmatic statements into question.
The following is a direct quote from a consultation with mineralogist
Paul Hlava, a leading authority on crystal structures, their composition,
physical and optical properties, and the interaction of light with the
structures and their properties. He emphasized that "this is not a thorough
and rigorous discussion of the causes of color in minerals or gems, which
is a very complicated subject in itself."
"It is now known that the production of color by trace elements often
involves the excitation of electrons of the transition metal elements
by absorption of specific energies from light", states Paul Hlava. "The
electrons move from their normal, ground state to a higher energy level
in the atom. The color we see is the "left over" light that has not been
absorbed. The electrons later fall back to the ground state by releasing
this energy in several steps and do not cancel the absorption process.
The density of the packing of the atoms in a crystal structure affects
the distance between the electron energy levels and influences what color
we perceive. Manganese is a `transition' element and, though other impurities
may be present, it is likely that it is responsible for our perception
of the different shades of morganite. The color may also be modified by
the presence of other transition metal element impurities, such as iron.
It would appear that no mineral/gem is actually colored by lithium or
cesium, although these elements are often found in colorful minerals.
The lithium and cesium have no more effect on the color than the silicon
and aluminum that are also present in these colorful minerals."
Many gemstone reference books provide numerous descriptions of morganite's
colors. The International Student Edition of Mineralogy by Kraus, Hunt
and Ramsdell describes morganite as "pale pink to rose red." Other references
use the terms pink, pale violet, apricot, peach, pale yellow-orange, and
pale brownish-orange. John S. White states in the Smithsonian Treasury
Minerals and Gems that "newly mined specimens of morganite are peach to
brownish-orange" and "after prolonged exposure to the sun, the color changes
to pink." Pictures of two stones from Brazil, a 235.5-carat pink gem donated
to the collection by Mr. and Mrs. Frank Ix, Jr., and a brownish-yellow
330-carat gem are shown on page 62 of the volume. Sinkankas notes in his
Gemstone and Mineral Data Book that apricot colored material from Brazil
altered to pink after a week of exposure to sunlight in San Diego, California.
Dr. Richard T. Liddicoat states that much of the pink morganite on the
market is yellow to reddish-yellow material from Brazil that has been
heat-treated. The color change takes place at 400 degrees centigrade.
Mineralogist Walter Schumann observes that the lower color quality material
can sometimes be improved by the heat-treatment process.
Miscellaneous facts gleaned from various sources during the research
for this article include the following information. Morganite usually
has higher refractive indices and a higher birefringence than the other
varieties of beryl. In the Color Encyclopedia of Gemstones, Dr. Joel Arem
lists the bixbite variety (red beryl) from the Thomas Range in Utah as
morganite. Beryl fuses with difficulty to a white pebbly or blister-like
material. Fusion causes the loss of its crystalline structure to become
singly refractive beryl glass. Simon & Schuster's Guide to Gems and
Precious Stones states that "morganite is not as a rule imitated, nor
is it produced synthetically." In the July 1995 issue of the New Mexico
Facetor, editor Merrill O. Murphy then warned of a glass imitation of
morganite that is difficult to detect visually. Synthetic morganite is
now being produced by Biros of Australia and was available at the Kimberly
booth at the AGTA Show in Tucson this year. These pale peach synthetic
gems were quoted at forty dollars per carat.
Richly colored morganite gems are among the more valuable of the secondary
gemstones. The value of morganite has increased with the expanding knowledge
of the gem-buying public. The more informed consumers become about gemstones,
the more it fuels the growing demand for colored gems. Freeform gems,
carvings, and new faceted designs join the popular and traditional step-cut
rectangle with truncated corners and are appearing in displays more frequently.
Beryl's combination of desirable physical properties and its many color
choices make the variety of morganite a gem suitable for all types of
|| beryllium aluminum silicate Be 3 Al 2 Si 6 O 18 + MnCsLi
|| silicate; cyclosilicate
| Crystal System:
|| hexagonal per Arem; hexagonal (trigonal) per Schumann
|| pink, rose, pale violet, pale yellow-orange, brownish yellow,
|| transparent, translucent, semi-translucent
|| stubby six-sided prisms, tabular
|| imperfect basal
| Fracture Lustre:
| Specific Gravity
|| varies from 2.60 to 2.90
|| 7.50 to 8.0
|| very good; can be brittle
| Refractive Index
|| o=1.572 to 1.592; e= 1.578 to 1.600
|| varies from 0.008 to 0.009
| Optic Character
|| uniaxial negative
|| distinct pale pink/bluish pink
|| may fluoresce weak pale violet
| Ultraviolet Fluorescence
|| no information
| Color Filter
|| no information
| Aqua Filter
|| no reaction
| Chelsea Filter
|| no reaction
|| insoluble except in hydrofluoric acid
| Thermal Traits
|| color change with moderate heat and light; avoid thermal shock
|| long hollow tubes may contain liquid; veils are common; coarse
tubes in pink Brazilian material can cause asterism