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 $2,000 to $2500. A similar cabochon from the Lone Mountain Mine, also closed, would be $750 to $800. 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 from the Skyhorse Mine from Tibet and China would be nearer $75 because it is still active and produces large quantities of turquoise.
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 $600 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.