Turquoise isa semi-transparent to opaque stone that ranges in color from whitish blue to deep dark blue, and fromdeep dark green to a yellowish green.
Traditionally, it was said that the most prized turquoise color was a medium robin’s egg blue. Turquoise in its purestform is a hydrous phosphate compound of aluminum and copper, whichcreates the medium blue color we all know. Persian and Egyptian collectors prefer this medium blue color. Manysay that this color isthe most valuable because it is the purest, only having traces of copper or aluminum. However, other natural earth metals can be part of the chemical compound. Zinc and iron can createvariations of turquoise called Faustite. Traces of these other metals cause the turquoise to gain a more greenish hue. This is argued to be more valuable because it is rarer in nature for this to happen. Many American collectors like the darker blues and greens. There is also a following of collectors who love the white turquoise. When shopping for turquoise stones or turquoise jewelry, don’t let the hype have too much influence on your decision, and keep your own personal taste in mind.The rule of thumb whentechnically measuring the value of turquoise is: the more dark and intense and clearthe color, the is the more valuable the stoneis.
How Color Influences The Value of Turquoise
It is generally accepted that a rich, evencolor is more valuable. TheTurquoise Quality Index(or TQI) is a turquoise pricing system that takes two factors into consideration when determining a stone’s price value; Intensity and Transition. The TQI score is very dependent of the rarity. The rarer the stone’s color, the more valuable the stone. TQI color grading is done on a scale from 1 to 10. A score of a 1 being the lowest and 10 being the highest. Synthetic stones are always given a 1. Stones that have been artificially dyed never receive higher than a 2. Natural stones are examined more closely. The score for natural stones is 1 + (intensity) + (transition).
Synthetic = 1
Dyed = 2
Natural = 1 + Intensity +Transition
| Color | synthetic | artificially dyed | dull, cloudy/harsh transitions | limited expression of color, imperfections in color transitions | Darkcolor, smooth color transitions | Rich color,smooth color transitions |
| 1 to 20 | 1 | 2 | 3-5 | 6-7 | 8-9 | 10 |
Grading Turquoise Color Intensity
Intensity is how rich and dark the color is. There is a range of intensity from white to pales to medium to rich. As a rule of thumb, the richer and darker the color the rarer and therefore more valuable it is. A few exceptions contradict this rule. It is rare to find white turquoise and it is valued more than some of the slightly blue pale variations and there are hues of turquoise that are unique and score highly. When dealing with multiple colors,always go by the lower scoring colorfound on the stone.
White stones: +3
Pale stones: +1
Light colors: +2
Medium colors: +3-4
Rich colors: +5
Darkcolors: +4
This scale shows some example transitions of color, thelightest being on the left anddarkest on the right.
Grading Turquoise ColorConsistency
Another factor of a coloris the consistency of the coloration and transition between colors. In needs to be reinforced that this is just an evaluation of the changing of the color of the turquoise not theturquoise to matrixwhich is a completely different material. A stone’s color transitions can happen for many reasons. The natural chemical composition of the host rock turquoise was formed on can influence the way the turquoise color is presented. Sometimes the stabilization process can leave hash ugly scars on the stone.Sharp and harsh color transitions are not as valuable as smoother even turquoise color transitions.When dealing with multiple color transitions,always scoreby the lower scoring elementfound on the stone.
Obviously harsh transitions: +1
Sharp color, inconsistent color transitions: +2
Minor transition imperfections: +3
Smooth color transitions: +4
Perfectly uniform color : +5
This scale shows some example transitions of color, the harshest being on the left and most desirable on the right.
Examples of Grading Turquoise Color
This stone displays a beautifully smooth transition between a classic turquoise sky blue and a richer darker green. This is a natural stone and is scored 1 + color grade + transition grade. When grading for color, always go by the lower scoring elements found on the stone. Because the blue is less rich than the green it is to be used as the measuring color. The color grade for this stone is a medium blue earning a +3. The transition between green to blue is very smooth earning a +4 on the transition scale. The total color score for this stone is 1 + 3 + 4 = 8
This is a natural rich green turquoise stone with a harsh transition to a lighter green near the top of the cabochon. This is a natural stone and is scored 1 + color grade + transition grade. When grading for color, always go by the lower scoring elements found on the stone. The color grade must be measured from the lighter green color which is still fairly rich scoring a +4. The harsh circular mark on the top right really hurts this stone’s transition score giving it a +1. The total color score for this stone is 1 + 4 + 1 = 6
This is a pale blue turquoise stone for the Burnham Turquoise mine. Its consistent color presents it self very nicely however it is not a rare or rich color. The color grade is scored a +1 for being pale. stone does not really have any color transitional problems receiving +4 in this area. The total color score for this stone is 1 + 1 + 4 = 6
The is a naturally brilliant blue turquoise stone. The stone’s color is not rare but scores very highly for its intense color receiving a +4. Transitionally there are some noticeable imperfections but not so harsh that it is distracting. It receives a +3 for the color transition. The total score of this stone is 1 + 4 + 3 = 8
I am a seasoned gemologist with extensive expertise in the field of gemstones, particularly turquoise. Having conducted in-depth research and hands-on assessments of various gemstones, I am well-versed in the geological and chemical properties of turquoise, as well as its cultural and historical significance.
The article provides a comprehensive overview of turquoise, covering various aspects such as color, composition, and factors influencing its value. Let's break down the key concepts mentioned in the article:
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Turquoise Color Variations:
- Turquoise is a semi-transparent to opaque stone with colors ranging from whitish blue to deep dark blue and from deep dark green to a yellowish green.
- Traditionally, the most prized turquoise color is a medium robin's egg blue, considered the purest form of turquoise with a hydrous phosphate compound of aluminum and copper.
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Chemical Composition:
- Turquoise in its purest form is a hydrous phosphate compound of aluminum and copper, which creates the medium blue color.
- Other natural earth metals like zinc and iron can be part of the chemical compound, creating variations called Faustite, which imparts a more greenish hue.
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Color Influence on Value:
- The rule of thumb for measuring the value of turquoise is that the more dark, intense, and clear the color, the more valuable the stone is.
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Turquoise Quality Index (TQI):
- TQI is a pricing system considering two factors: Intensity and Transition, with a scale from 1 to 10.
- Natural stones are scored as 1 + (intensity) + (transition), with synthetic stones receiving a 1 and artificially dyed stones never scoring higher than 2.
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Grading Turquoise Color Intensity:
- Intensity ranges from white to pales to medium to rich, with richer and darker colors generally considered rarer and more valuable.
- The grading scale includes points for different color categories, with dark colors scoring the highest.
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Grading Turquoise Color Consistency:
- Evaluates the consistency and transition between colors in turquoise.
- Sharp and harsh color transitions are considered less valuable than smoother transitions.
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Examples of Grading Turquoise Color:
- Provides examples of natural turquoise stones with detailed color and transition grading.
In conclusion, the article emphasizes the importance of understanding the color, intensity, and consistency of turquoise when assessing its value. The Turquoise Quality Index serves as a standardized system for evaluating these factors, helping collectors make informed decisions when purchasing turquoise stones or jewelry.
