Turquoise Quality
An article by Lee Anderson
We could write pages on this and still not cover the subject.
In the earliest of times — up to the late 1800s — certainly,
the pure blue without matrix was considered the best. It was time-tested;
if the color did not change it was “old rock”…in
other words, a gem! If the color did change, it was “new rock,”
inferior and impermanent. While the pure blue stone could be gem
quality, the matrixed stone was not considered a gem stone. This
all changed in the late 19th century, when the American Indian developed
a preference for the matrixed stone, causing an entire new grading
criteria to evolve.
Today, the preferred turquoise in the Middle East is still the
pure blue. As such, great quantities of rather inferior stabilized
“chalk” turquoise have been shipped there for sale to
local jewelers and merchants. People have brought me pieces they
bought in bazaars and markets as “old Persian or Arab”
jewelry that was actually made from Kingman stabilized turquoise.
Beware!
Criteria for Grading Turquoise in the U.S.
Hardness / Density. This is a critical factor
in determining the grade of a turquoise specimen. An inferior, chalk-like
turquoise will feel light; it will be porous and stick to your tongue.
The harder, denser pieces will have a “good” substantive
feel to them. They will not draw the same quantity of moisture from
your tongue as lower grades, but you will feel some adhesion to
your tongue. As density increases, so too does hardness. Just as
turquoise varies from a little over 2 to nearly 6 on the Mohs scale,
its specific gravity also varies but typically is 2.8, like quartz.
Luster. This should come from within the stone
— not just from a surface polish.
Color. No area is less codified than this. The
ancients preferred blue because a gem-grade blue stone would not
change color (King Tut’s treasures include a substantial amount
of blue turquoise — it appears today unchanged). Because the
softer blue stones would eventually start turning greenish, it was
assumed that green was not as good. Time has proven this wrong.
Some green-hued turquoise such as Skyhorse, China Mountain (both
are names given to turquoise from China), Cerillos, Blue Gem, and
Fox, to name a few, are ranked in the top three grades, like blue
stones from the Lander, Lone Mountain, Red Mountain, Morenci, and
Bisbee mines. To make matters even more difficult, some mining areas
— such as Skyhorse, China Mountain, Blue Gem, and Royston
— produce both colors.
Matrix. This is the host rock in which the turquoise
forms and bonds. When cut, the host rock and the turquoise are one
piece. The pattern of this matrix must be pleasing. This is subjective
at best, but with experience, you learn what most people consider
most desirable. Again, as in color, the opinions on which matrix
is “best” varies dramatically. There are hard-core supporters
of the fine, dark, spider web found in the Lander, Number Eight,
Lone Mountain, Red Mountain, Skyhorse, and China Mountain mines.
The heavy brown-black matrix of Bisbee and Tyrone has followers
who believe it is the world’s best. A hard, lustrous cabochon
from Morenci typifies another beautiful and highly regarded matrix.
It is freeform, with a blending of webbing and deep pattern matrix
combined with visible pyrite inclusions.
In a given cabochon of turquoise, any of the above could qualify
as “best.” depending on the personal preferences of
the one judging. However, when mounted in jewelry, you must consider
the balance of the turquoise in the setting by itself or in combination
with other stones.
Rarity. People covet that which is rare, and
value escalates accordingly. A stone from a mine that produced a
highly collectible stone that has subsequently closed appeals more
to a collector then a stone from an active mine. Again, the other
factors discussed above must also apply; rarity is simply the price
discriminator. For example, a beautiful five-carat cabochon of deep-blue
turquoise with a tiny black spider web matrix from the Lander Mine
in Nevada (closed many years ago) has a retail value of $300 to
$500. A similar cabochon from the Lone Mountain Mine, also closed,
would be $200 to $300. It is every bit as good — and, in the
case of the matrix, better — but the mine produced for a longer
time. A similar cabochon (a term used to identify a superior grade
of turquoise) from the Skyhorse Mine from Tibet and China would
be nearer $50 because it is still active and the turquoise has yet
to be properly publicized.
Grades of Turquoise
Turquoise grading, again, is a subjective area; however, the following
criteria are accepted by a good many in the trade. Note that percentages
cited below should not be taken as exact. They are a “best
guess” based on our experience of over 35 years.
1. Gem. For a stone to be considered a gem, all
of the criteria listed above must be met except the rarity factor.
Less then 1 percent of all turquoise can be legitimately called
“gem.” Remember — rarity affects value, not natural
quality.
2. Very High Grade. Stones of this grade are nearly
perfect and exhibit the same general characteristics as gems, except
that the matrix patterns may not be perfectly balanced. The stone
would still be quite hard and lustrous. About 3 percent of all turquoise
is very high grade.
3. High Grade. Turquoise of this grade is used
in most high- but not competition-quality jewelry. It is hard but
not as hard, balanced but not perfect — in other words, a
very attractive specimen that could be just a bit better. Luster
must be perfect. About 5 percent of turquoise fits this grade.
4 a/b/c. Jewelry Quality / High Quality / Investment Quality
(note that the word “grades” is omitted). It should
have a good hardness and feel, and it should not need stabilization.
It must have a nice luster but not necessarily be as deep as higher
grades. The matrix pattern should be attractive but probably a bit
unbalanced. Although this stone could be stabilized to prevent color
change, doing so is unnecessary because it will change slowly yet
remain attractive nonetheless. Approximately 10 percent of turquoise
is in this category.
5 a/b/c. Mine Run / Average Quality / Good Quality / Stock.
This is a very average turquoise that needs no stabilization because
it holds polish and stays attractive. Stabilizing, however, improves
the stones by strengthening it for carving and permanence. We estimate
that about 20 percent of turquoise falls within this category.
6 a/b/c. Chalk / Bulk / Chip Stock / “Levarite”
(as in “leave ‘er right there”). This
stone is soft, porous, brittle, and of little value to the jewelry
industry until stabilized. Frequently, the color is insufficient,
so pieces are “color enhanced” or “color shot”
— in other words, artificially colored. Most turquoise falls
into this category. One reason is that mines have needed to become
deeper as shallow turquoise deposits have been removed. As our article
on the origin and occurrence of turquoise indicates, the deeper
the deposit, the lower the quality.
Conclusion
Turquoise is considered a precious stone. At one time in history,
superior specimens were valued by weight, more than gold. Today,
turquoise ranges from a few cents per carat (chalk) to over $50
per carat for a superb gem stone. It is widely regarded as our nation’s
“national stone.” Man has coveted, romanced, fought
for, and owned this remarkable stone with pride.
References / Recommended Readings
John Adair, The Navajo and Pueblo Silversmiths, University
of Oklahoma Press, 1944.
Margery Bedinger, Indian Silver, Navajo and Pueblo Jewelers,
University of New Mexico Press, 1973.
M.G. Brown, Blue Gold, The Turquoise Story, Main Street
Press, Anaheim, CA, 1975.
Larry Frank, Indian Silver Jewelry of the Southwest, Schiffer
Publishing Ltd., Westchester, Pennsylvania, 1990.
The International Turquoise Annuals, vol. I and II, 1975
and 1976 (only two published) Impart Pub, Reno, NV. Note in vol.
I the article on pages 31–55 by D. Allen Penick, “Turquoise,
the Mineral that’s an Accident.”
Carl Rosnek and Joseph Stacy, Skystone and Silver, Prentice
Hall, Englewood Cliffs, New Jersey, 1976.
Joseph E. Poque, Ph.D, The Turquoise, A report to the
National Academy of Science, vol. XII, Second and Third Memoir,
1915. Reprinted in 1974 by Rio Grande Press, Inc., Glorieta, NM.
(This reprint includes a foreword and details on Southwestern turquoise
mines by Rex Arrowsmith and an excellent reference list. )
Stuart A. Northrop, Turquoise and Spanish Mines in New Mexico,
University of New Mexico, Press, 1975.
Stuart A. Northrop, David L. Newman, David H. Snow, Turquoise,
reprinted by General Printing and Paper Co., Topeka, KS. A reprint
from El Palacio, vol. 79, No. 1, 1973, Museum of New Mexico.
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Related Indian Jewelry Articles by Lee and Eric Anderson
• “The
History of American Indian Jewelry”
• “The
Squash Blossom Necklace”
• “Turquoise
in Indian Jewelry”
• “How
the Quality of Turquoise Affects Its Use in Jewelry”
• “Stones
Used In Indian Jewelry”
• “The
History of Turquoise”
• “The
Origin and Occurrence of Turquoise”
• “The
Physical Properties of Turquoise”
• “Natural,
Stabilized, Treated, Fake, and Synthetic Turquoise”
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