Turquoise
Grading How to Guide.
(Part Two)
In part 1 We looked in depth at first
Color, and secondly the Matrix with are part of
(TQI) Turquiose Quality Index. You will need the charts from part 1 to
compleat the TQI grading process. These exsaminations and the grading charts of
the TQI will help us to grade and value our turquoise. Today Turquiose can be
worth a few pennys to $2,000 a carat. Rough turquise can range $1 to $25 per
carat or gram ( 1 gram = 5 Carats), for the most common found on the market, of
course rarer turquoise were the mines have closed are much more exspensive. US
southwest turquiose also comands a premeum for the higher grade and rare
turquoise. As we discussed in part one putting a price tag on our turquoise is
somewhat subjective, and will change overtime, you never know if someone will
find a small pocket of a new variety of turquoise. We will look at several
other charts of grading that include, the 1st. structure, structure includes
the following exsamination and scoring catigories, composition, hardness, enhancement,
and cut, and 2nd rarity, rarity includes avalibility, contigous
size, color and matrix (Color &
Matrix covered in part 1) These charts and eight areas of exsamination will
help in determining a price tag or value on our turquiose.
*The next four catigories of exsamination make up the
“Structure” Catigory
Hardness
In our blog “How to be a Rockhound”
we discuss hardness, and the Mohs Scale.
You don’t want to destroy the stone so its best to determine the hardness
before polishing, if it’s a finished piece it should be in a range between 3 to
6. Clowdy stones will generaly scale low and gemmy will range on the high end
of the scale. Poor quality stones 1 to 5 on our scale noted below. Chalky or
brittle natural, or lower quality stabalized stones grade get a 10.
Professionally stabalized stones receive no higher than 15.Rare natural
untreated stones of a hardnes over 5 will receive the highest score a 20. If
you have to guess on any category go 5 points lower espesialy on 5+ hardness.
Hardness
|
Plastic
|
Chalk
|
Reconstituted
|
Below
5 on MOHS scale
|
Pro
stabilization 5+ on MOHS scale
|
High
natural hardness MOHS scale 5+
|
1 to
20
|
1
|
3
|
5
|
10
|
15
|
20
|
Conclusion; Hardness 1 to
20 possible points with most stones falling between 5-15. If a hardness test
will damage the stone do not over guess on this scale. Scoring is between 1-20
Enhanced
A natural high-quality stone of 5+ on the
MOHS will often command a higher price. At the same time some high quality and
rare stones may gain value by a enhancement such as a stabilized turquoise,
that has been hardened for durability, some enhancements are acceptable and do
not adversely affect value, however reconstituted or engineered turquoise is
valued less and so to plastic is not of value. So, a caulk turquois with good
color and or pattern would score low on our scale a 5, if it were to be
enhanced with a high-quality stabilization could receive a 13-19 on our scale.
Enhancement
|
Plastic
|
Reconstituted
|
Heavy Stabilization/Dyed
|
Pro Stabilization Waxed/Oiled /
Zachary Process
|
Natural
|
Chalk
|
1 to
20
|
1
|
2-5
|
6-12
|
13-19
|
20
|
5
|
Conclusion; Enhancement scores range from
1-20
Composition
The materials that make up the stone are its
composition. Much of the turquoise that is mined is considered chalky, the
amount of chalkiness is also a gauge for grading and scoring value. If it’s powderier
its less value due to the lower quality. Turquoise also has host rock and possibly
varying amounts of matrix of other minerals or rock, these to increase or decrees
the value of the stone. The rarer and more desirable the composition the higher
the value and the higher the score.
Composition
|
Plastic
|
Reconstituted/Chalk
|
Required stabilization
or unstable host rock/ high calcite and quartz in matrix
|
stabilization
and minor imperfections in matrix
|
pro
stabilization pure natural turquoise/ solid matrix
|
rare
elements in matrix
|
1 to
10
|
1
|
2-3
|
4-5
|
6-7
|
8-9
|
10
|
Conclusion; Composition
grading scores are 1-10 and are one part of four areas to grade Structure.
Cut
It may take a long time to cut turquoise,
however that makes little difference in the price. It’s a good cut that is
expected, a great cut can add to overall value. Raw stones often need cut and
polished to add value, the scoring is as follows. Stones can be rolled and polished
and machined to standard size cabochons for mass production. Stones can be made
into cabochons by a machine or can be hand cut and shaped cabs, or stones can be
sculpted by an artist.
Cut
|
raw
|
rolled or cut
|
standard machine cab
|
hand shaped cab
|
hand sculpted design
|
||
1 to 5
|
1
|
2
|
3
|
4
|
5
|
||
Conclusion; Cut can add to
value and is the last part of the “structure” evaluation, with scores ranging
from 1-5.
Structure makes up 55 points:
Hardness Maximum 20, Enhancement Maximum 20,
Composition Maximum 10, and Cut Maximum 5.
Structure
|
Hardness
|
Enhancement
|
Composition
|
Cut
|
55
points (total)
|
20
|
20
|
10
|
5
|
The
next two categories + Part 1 of turquoise grading categories, color &
matrix make up a total of four categories of examination make up the “rarity”
category.
Contiguous
Size
The total size of the
stone is what we are looking at. In some situations, cutting out a perfect rare
or higher grades section of a stone will be wise, because you always grade a
stone based on the lower qualities of say color, matrix and other attributes,
it really depends on the stone. But a high-quality stone that is larger will be
worth much more usually. This is because larger stones are harder to come by.
See the grading chart below.
Contiguous size
|
smaller than 1/4″
|
1/4″ to 1″
|
1″ to 2″
|
2″ to 4″
|
4″ +
|
1 to 5
|
1
|
2
|
3
|
4
|
5
|
Conclusion; a stone
that is less than ¼” at its widest point gets 1. Between ¼” and 1” grades a 2
and so on. Beyond 5” would be considered a specialty and the market price will
vary higher.
Availability
How Available is the
turquoise? If is readily available as plastic turquoise, it’s not valuable and
will grade a 1 on our scale. If it engineered from dust or chips it will grade
a 3 on our scale. If the stone comes from a top mine of a small amount mined
and is deemed unavailable, it will rate higher for rare and high-quality
turquoise, were a mine that has and continues to supply a larger amount of
turquoise will be lower. The different colors, grades and patterns also play a
roll. Large production mines such as China receive a 6 on the scale, and
Kingman receives a 12 on the scale. Rarer US mines with smaller production receive
13-17 points on the scale. The rare Lander Blue and a few hat mines score 18-19
on our scale. Very rare fossil turquoise include fish, mouse teeth, shells and
petrified wood will receive a 20 on our scale.
Availability
|
Synthetic
|
Chalk/Chips
or Reconstituted
|
Common
Mine
|
Uncommon
Mine
|
Rare
Hat Mine or Rare Specimens
|
Extremely
Rare
|
1
|
3
|
6-12
|
13-17
|
18-19
|
20
|
Conclusion;
Availability score between 1-20 is one of the four areas that are graded for
the “Rarity” grading category.
Rarity
Rarity chart consists or four category’s,
Availability/Origin, Color, Pattern, Contiguous size, for a maximum total of 45
points. Color and Matrix were covered in Part 1.
Rarity
|
Availability
|
Color
|
Matrix
|
Contiguous Size
|
45 points (total)
|
20
|
10
|
10
|
5
|
*Turquoise price = Turquoise Quality
Price / Carat Index, or (TQI) X Carat Weight
Weight
of the stone
The greater the weight of
the stone the more valuable it will be. Pricing for medium grades will usually
be by the Gram, high grade and rare will be by the carat. $1 dollar a carat
turquoise = $5 a gram. Price per carat depends on how high the TQI grading
score is. Charts vary, the one at the bottom has been adjusted by what I have
seen in the market and is subject to change. Note if the stone has a backing
the weight will not be accurate and an estimate will have to be made, by
figuring out the amount of backing, this can be 40 to 60 percentage of the
total stone mass. Also, if the stone is set in a setting an estimate will need
to be given. See the GIA link below to help you estimate the gem weight.
Turquoise
Value TQI Price per Carat
Evaluate and grade your turquoise stone and
take the total TQI points compare it to our chart below to get a price per
carat. Numbers based off 2013 price list
TQI
|
Price/Carat
|
TQI
|
Price/Carat
|
TQI
|
Price/Carat
|
||
8-16
|
$0.01
|
56
|
$0.46
|
79
|
$6.35
|
||
17-34
|
$0.02-$0.05
|
57
|
$0.53
|
80
|
$6.50
|
||
35
|
$0.05
|
58
|
$0.60
|
81
|
$7.00
|
||
36
|
$0.06
|
59
|
$0.65
|
82
|
$7.50
|
||
37
|
$0.07
|
60
|
$0.69
|
83
|
$9.00
|
||
38
|
$0.08
|
61
|
$0.75
|
84
|
$9.50
|
||
39
|
$0.09
|
62
|
$0.80
|
85
|
$10.00
|
||
40
|
$0.10
|
63
|
$0.89
|
86
|
$20.00
|
||
41
|
$0.11
|
64
|
$0.95
|
87
|
$30.00
|
||
42
|
$0.12
|
65
|
$1.08
|
88
|
$42.00
|
||
43
|
$0.13
|
66
|
$1.20
|
89
|
$54.00
|
||
44
|
$0.14
|
67
|
$1.42
|
90
|
$71.00
|
||
45
|
$0.15
|
68
|
$1.65
|
91
|
$90.00
|
||
46
|
$0.16
|
69
|
$1.85
|
92
|
$125.00
|
||
47
|
$0.18
|
70
|
$2.20
|
93
|
$150.00
|
||
48
|
$0.19
|
71
|
$2.65
|
94
|
$180.00
|
||
49
|
$0.21
|
72
|
$3.45
|
95
|
$215.00
|
||
50
|
$0.23
|
73
|
$4.05
|
96
|
$260.00
|
||
51
|
$0.25
|
74
|
$4.75
|
97
|
$320.00
|
||
52
|
$0.27
|
75
|
$5.20
|
98
|
$385.00
|
||
53
|
$0.30
|
76
|
$5.50
|
99
|
$500.00
|
||
54
|
$0.34
|
77
|
$5.85
|
100
|
$1,000.00
|
||
55
|
$0.39
|
78
|
$6.15
|
||||
Use
the above charts as a guide for finding the TQI. Each indicator has
a list of characteristics and a point value marked below. (for
example, if you have a piece of reconstituted turquoise the hardness it
earns 10 points) Add the points together to get the total TQI point value.
Turquoise
Quality Index
The Turquoise Quality
Index (TQI) is a measurement of the quality of the turquoise stone. The TQI is
a number on a scale between 8 and 100. The higher the TQI number, the better
quality the turquoise, the higher the grade and the more valuable the stone.
High numbers are rare; less 1% of turquoise on the market will score a 90
or higher.
Turquoise Quality Index
|
||||
TQI Score
|
Grade
|
Market Grade %
|
Price per Carat
|
|
90-100
|
AAAA
|
Superior
|
less than 1%
|
$50-$2000
|
85-89
|
AAA
|
High
|
2%
|
$10-$50
|
75-84
|
AA
|
5%
|
$2.50-$10
|
|
65-74
|
A
|
Medium
|
10%
|
$1.00-$2.50
|
35-64
|
B
|
Low
|
22%
|
$0.05-$1.00
|
17-34
|
Reconstituted
|
Fabricated
|
60%
|
$0.02-$0.05
|
8-16
|
Synthetic
|
$0.01
|
||
Conclusion;
Turquoise price = Turquoise Quality Price / Carat Index, or (TQI) X Carat
Weight
TQI
With our charts we can
use the TQI grading and scoring system to obtain a reasonable estimate of value
for a turquoise specimen, however, as is with most scoring or grading systems
it can be subjective and change with time. It is our hope that with the two-part
series and charts that the scoring and grading tips that you the reader will
have a greater understanding of the subject. We have included links for more
information on Turquoise, books guides, information, and our social media links
as well. The chart below is to be used in conjunction with part 1 and part 2 of
this Turquoise Grading guide and is for entertainment and information only.
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Turquoise
Guides
Reference
for more information https://www.researchgate.net/publication/322465744_Turquoise_Grading_in_Persian_historical_and_modern_times_a_comparative_study
Turquoise
Value References
Fritsch, Emmanuel.
McClure, Shane. Ostrooumov, Mikhail. Andres, Yves. Koivula, John. Kammerling,
Robert. The identification of Zachery treated Turquoise 1999.
Website pdf : http://image1.fmgstatic.com/pdf/The-Identification-of-Zachery-Treated-Turquoise.pdf
Mohs Hardness Scale, A rapid hardness test
for field and classroom use.
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