Gemstone Color Measurements and Specifications


One of the great challenges of gemology is the development of an accurate, simple, consistent, and reproducible technique for gemstone color measurements and specifications. Until the mid-80s little progress was made, despite the appearance and widespread promotion of various color-chart systems. None of these systems are satisfactory for gemology, chiefly because: 1. They don’t adequately cover the total range of gem colors, 2. They don’t offer enough detail in the ranges they do cover, and 3. The color-chart materials (printed colors and transparencies) are of insufficient quality to prevent variations in production runs. The ideal solution is a gemstone colorimeter. However, such an instrument must deal with the unique optical properties of gems, such as brilliancy and pleochroism, which make gemstones extremely difficult specimens for instrumental measurement.

Figure 3. Munsell color wheel. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.19; courtesy of Minolta Camera Company, Ltd. Japan.)
Munsell color wheel. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.19; courtesy of Minolta Camera Company, Ltd. Japan.)

Three-Dimensional Color Space

The science of colorimetry is well established in almost all areas of endeavor where color is important, such as paint, plastics, textiles, and other industrial and consumer materials. Objective instrumentation is now routinely used in these fields. However, before such instruments were available people had to rely on visual systems such as color charts for specifying color. These charts are sections of what we may refer to as three-dimensional color space. These dimensions are termed hue, lightness, and saturation.

Hue

Hue is the attribute we are describing when we speak of red, yellow, green, blue, purple, and other hues intermediate to adjacent pairs in this series. These hues can be readily visualized in terms of a color wheel.

Lightness

Also called value, lightness is a scale with white and black as endpoints and shades of gray in between. Note, however, that all chromatic colors can also be scaled to lightness as a function of their total reflectance. Lightness can be visualized in terms of a vertical axis with white at the top and black at the bottom.

Figure 1. Three-dimensional color system. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.8; courtesy of Minolta Camera Company, Ltd. Japan.)
Three-dimensional color system. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.8; courtesy of Minolta Camera Company, Ltd. Japan.)

Saturation

Also called chroma, saturation is a measure of the amount of hue in a color, its vividness, or how much it differs from a gray of the same lightness. Chroma can be seen in vertical sections of three-dimensional color space. A section along a specific radial direction of the color circle is designated as a specific hue. Lighter shades of this hue are near the top of the section, darker shades at the bottom. The chroma (vividness) of the hue increases moving outward from the central axis. The range of chroma varies with both hue and lightness, making the color solid an irregular shape, rather than a simple ovoid or sphere.

Figure 2. Color solid. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.9; courtesy of Minolta Camera Company, Ltd. Japan.)
Color solid. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.9; courtesy of Minolta Camera Company, Ltd. Japan.)

Color-Order Systems

Subdividing the color solid into smaller units and giving each a name or set of numerical coordinates can achieve color specification. This results in a classification known as a color-order system. The color solid can be subdivided in many ways. Not surprisingly, there are also many color-order systems.

Some of the color-order systems created during the early decades of the 20th century were represented by charts made of paint colors coated on paper. Architects and designers used Wilhelm Ostwald’s system for color selection and specification. Biologists used Robert Ridgway’s system for classifying thousands of flora and fauna specimens. (Some of these older systems, like Ostwald’s and Ridgway’s, are still used today). Thus the need for accurate color measurements and specifications was firmly established before instruments and related color-order systems were available.

The A.H. Munsell System

Perhaps the most popular and widespread of the chart-type color-order systems is the one devised by A.H. Munsell and extensively revised by the Optical Society of America (OSA) in 1943. The Munsell hue scale is based on five hues equally spaced around the hue circle (red, yellow, green, blue, purple) and intermediate hues (yellow-red, green-yellow, blue-green, purple-blue, red-purple). The major hues are abbreviated R,Y,G, B, and P, and the intermediate hues YR, GY, BG, PB, and RP.

Further subdivision results in forty hue charts in the Munsell Book of Color. Colors appear on these charts at value (lightness) intervals of one unit from 2 to 9. Chroma (saturation) is represented in whole units ranging from 2 (near-gray) in two-step intervals up to as high as 14 and 16 for the most vivid colors.  The notation system is decimal, allowing colors to be specified accurately. Munsell color books are available in both matte and high gloss finish, with the latter having about fifteen hundred colors.

Figure 4. Munsell value and chroma for hue 5G. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.17; courtesy of Minolta Camera Company, Ltd. Japan.)
Munsell value and chroma for hue 5G. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p.17; courtesy of Minolta Camera Company, Ltd. Japan.)

All these color-order systems (including the more recent German standard DIN 6164 and the Swedish Standard Natural Colour System) have certain similarities. Color sampling is along lines of constant hue (or a similar metric). Thus, corresponding colors on adjacent hue charts become visually farther apart as they become progressively more saturated (that is, move further away, radially, from the center of the color circle). Thus, the most vivid colors are more distant from each other than less vivid ones, often by a factor of five or more.

These color charts are inadequate for gemstone color measurements because they don’t have sufficient colors in the vivid color regions and they don’t extend far enough for gem analysis. The color ranges of vivid, transparent gemstones simply can’t be captured with opaque colors on paper. In addition, opaque paint colors don’t look like transparent gemstones, even when the colors are, in fact, the same.

The CIE System

A major step forward came in 1931 when the international adoption of the Commission Internationale de l’Eclairage (CIE) system resulted in greater interest in color measurements and specifications, especially by colorimetry. The CIE system included standard illuminants (incandescent, sunlight, north daylight), a standard observer, and standard response functions of the human visual system. The CIE continues as the principal international organization in the field of color research and standardization. Since 1931, it has made important improvements and additions to the original concept.

The color industry was built around research and development of spectrophotometers and colorimeters capable of making measurements and reporting data in CIE terms. However, this created a problem with existing color-order systems. Such systems are necessarily spaced visually for their appearance under a specific light source. Visual spacings and overall appearance will be altered accordingly if other sources are used. If CIE data are published for such colors, the numbers are valid only for the light source for which the measurement data were computed.

CIE color space is visually non-uniform. A more uniform color space makes specification of tolerances and small color differences more meaningful and is therefore more useful to science and industry. Extensive research has been done to produce mathematical transformations of CIE data into a more visually uniform color space.

The Hunter System

In 1942 Richard S. Hunter designed a filter colorimeter for the measurement of opaque surface colors and, to accompany it, the Hunter color-order system. This is a transformation of CIE data using simple equations that were incorporated into the computational elements of the instrument. Hunter space was of the “opposite-hue” or “opponent-hue” type as shown below.

Figure 5A. Lab color space as conceived by Richard S.Hunter
Lab color space as conceived by Richard S.Hunter

When Hunter a attribute is positive, the color has redness; when negative, greenness. Similarly, when b is positive the color has yellowness; when negative, blueness. The third Hunter attribute was L for lightness. Equal steps along the three scales (L,a,b) were intended to represent equal visual steps in the several color directions, permitting color differences to be simply computed by the formula:

ΔΕ= √(ΔL²+ Δa²+ Δb²)

Where delta (Δ)Ε denotes color difference.

It’s common practice today for color-measuring instruments to include Hunter color notations as a readout option for measurement results. Although material color samples were never produced to illustrate Hunter color space, the nearly uniform visual spacing became very useful for describing color specifications and tolerances in industry and contributed importantly to the sale and use of these instruments.

CIELAB Space

The CIE and others continued working to provide a color space with improved visual spacing. In 1976, CIELAB space was recommended. Similar to Hunter space, CIELAB space is a mathematical transform of CIE data and is plotted on rectangular coordinates. CIELAB color attributes are designated L* (L-star), a* (a-star), and b* (b-star) to distinguish them from Hunter and have the same nominal meanings. As with Hunter, CIELAB is a standard readout on current instruments.1

Figure 6. L*a*b* and Munsell notations (hue, value). For extremely small or large a*b* values, multiply or divide them by an appropriate amount before plotting and reading the hue values.(From Precise Color Communication: Color Control from Feeling to Instrumentation, p. 19; courtesy of Minolta Camera Company, Ltd. Japan.)
L*a*b* and Munsell notations (hue, value). For extremely small or large a*b* values, multiply or divide them by an appropriate amount before plotting and reading the hue values.(From Precise Color Communication: Color Control from Feeling to Instrumentation, p. 19; courtesy of Minolta Camera Company, Ltd. Japan.)

The OSA-UCS System

The Optical Society of America-Uniform Color Spacing system (OSA-UCS), an opponent-hue system developed by the Optical Society of America, is not only an improvement over Munsell spacing but is also a direct CIE transformation. The OSA-UCS colors (at this writing 558 colors, available as 2 x 2 inch samples) are in scales with intervals of two units in chromaticity and one in lightness. A prototype OSA color collection produced in Denmark shows chromaticity scale intervals of only one unit, with lightness increments of 0.5 and over two thousand colors. The OSA-UCS colors are the best example of uniform color spacing produced to date and will probably appear soon as a readout option on instruments.

Gemstone Color Measurements

Some gemologists have tried unsuccessfully to use existing color instrumentation to characterize gemstones. Instrument makers haven’t perceived gemology to warrant the costly research and development necessary to devise instruments specifically applicable to gemstones. The existing color charts and simplistic optical devices currently in use by gemologists are severely limited in accuracy and usefulness.

The recent marketing by Minolta Camera Co. of a lower cost portable colorimeter motivated several researchers to modify this instrument for gemstone colorimetry. One of the first was Dr. Richard Pettijohn. He attempted to adapt the Minolta sensor unit for specific use with gemstones by reducing the beam size and adding a glass plate to hold the sensor and a small mirror to reflect light passing through the stone to the sensor. However, this arrangement was too inaccurate and non-repeatable to be a viable solution. Moreover, the mirror arrangement dictates the “standard” illuminant for measurement to be the xenon flashlamp built into the unit rather than an independently measured white standard.

J. Rennilson and W.N. Hale devised an improved version of this instrument, also using the Minolta colorimeter. This replaces the glass and mirror with a small white-lined integrating sphere. A 2-mm light beam from below illuminates a gemstone mounted on a clear plate centered within the sphere. Light reflected from the gem is mixed with that transmitted through it and picked up by a detector outlet in the sphere wall. This colorimeter, with patented illuminating and collection geometry, is sufficiently accurate and repeatable for gemstone work. The data readout is in CIE data (Y,x,y) and CIELAB (L*,a*,b*), for CIE standard illuminant D65 or C (both representative of standard daylight in slightly different form). This kind of instrumentation will likely totally revolutionize the gemstone field, bringing order and objective reality to a chaotic system of vague and often obsolete terminology for gemstone color measurements and specifications.

The Rennilson-Hale instrument was not yet available when the Table of Gemstone Color Measurements at the end of this article was prepared. The Pettijohn instrument was therefore used. The illuminating and viewing geometry produce results that are neither as accurate nor consistent as the integrating sphere/fiber optic system of Rennilson and Hale. Also, the conversion of CIELAB data to Munsell notation was done by the Minolta DP-100 micro-computer.2

Table 3 Munsell (chroma C) and L*a*b* (chroma c*) notations Source: (From Precise Color Communication: Color Control from Feeling to Instrumentation, p. 19; courtesy of Minolta Camera Company, Ltd. Japan.) Note: In columns with two digits, left figures are for hues 1-5 and right for hues 6-10
Munsell (chroma C) and L*a*b* (chroma c*) notations
Source: (From Precise Color Communication: Color Control from Feeling to Instrumentation, p. 19; courtesy of Minolta Camera Company, Ltd. Japan.) Note: In columns with two digits, left figures are for hues 1-5 and right for hues 6-10

Errors in conversion may arise due to the limited data storage capacity of this device.3 Further errors are inevitable when trying to illustrate gemstones by photography and printed reproduction on paper.4 Therefore, the tabulated numerical color data must not be considered accurate enough to establish benchmark points for specific gemstone species. However, this degree of error is small compared to the actual variation in color exhibited by most species. The real purpose of this article and these measurements is to establish, for the first time in the gemological literature, the nomenclature, direction, and methodology for scientific, accurate, reproducible, and objective gemstone color measurements and specifications. The numbers themselves are considered less important in this context than an understanding of how they were obtained and the implications of this new technology for gemology and the gemstone marketplace.

NOTES

Dr. Joel Arem is deeply grateful to W. N. Hale, Jr., private color consultant and 22-year veteran of Munsell Color Co., Inc. (as both president and technical director), who provided substantial portions of this text. (Hale Color Consultants, Inc., 1505 Phoenix Road, Phoenix, MD. 21131)

  1. In CIELAB terminology, chroma is calculated from a* and b* as follows: Chroma = C* =√(a*²+b*²)
  2. Invaluable assistance in converting measured L*a*b* values to Munsell numbers, along with many valuable suggestions, was provided by Richard E. McCarty of Silver Spring, Maryland.
  3. Color data on gemstones reported herein are in the form of CIELAB readout and corresponding Munsell notation. The conversion to Munsell numbers are direct CIELAB conversions. No attempt has been made to simplify the resulting Munsell values in accordance with the limited range of actual Munsell color samples. This approximation is left to the reader.
  4. Many of the gemstones photographed in Arem’s Color Encyclopedia of Gemstones were measured with the Pettijohn-Minolta colorimeter. These gems are cross-referenced by notation in the section of color plates at the back of Arem’s Color Encyclopedia, and the tabulated color information herein refers to specific gemstone colors, shapes, and weights, facilitating easy correlation with photographs.

TABLE OF GEMSTONE COLOR MEASUREMENTS

GemstoneColorWeightShapeLocationL*a*b*Munsell
Actinolitedark green0.63Tanzania56-7.79.17.6GY 5.5/1.7
Adamitelight green0.86Mapimi, Mexico82-0.626.03.2Y 8.2/3.8
Andalusitebrown-green9.55emerald cutBrazil58-3.549.05.7Y 5.7/6.9
light brown-green4.72antiqueBrazil601.014.11.9Y 5.9/2.1
medium brown-green2.92roundBrazil381.620.02.8Y 3.7/2.9
Anglesiteyellow6.99fancyMorocco752.750.02.1Y 7.4/7.4
Amblygonitelight yellow10.10roundBrazil805.311.45.3YR 7.9/2/1
light yellow24.6antiqueBrazil95-3.520.06.0Y 9.4/2.8
Apatiteviolet0.59emerald cutMaine7110.315.03.1P 7.0/4.0
violet1.02hexagonMaine756.0-7.24.9P 7.5/2.0
yellow-green8.05rhomboidCanada68-11.332.11.9GY 6.7/4.5
yellow8.70antiqueMexico83-6.236.06.7Y 8.2/5.0
dark blue0.55roundBrazil34-10.2-40.69.7B 3.3/10.4
medium blue0.86ovalBrazil52-22.8-25.94.6B 5.1/7.8
gray-blue0.77roundBurma50-7.51.04.6BG 4.9/1.5
light green12.40round?42-6.29.85.3GY 4.1/1.6
dark green2.87roundBrazil31-16.412.30.1G 3.0/3.2
medium green1.09roundBrazil61-11.211.98.5GY 6.0/2.4
light blue1.07emerald cutMadagascar76-20.2-4.17.0BG 7.5/4.2
Axinitemedium brown1.45roundBaja, Mexico4210.79.310.0R 4.1/2.6
dark brown8.0pearBaja, Mexico2114.220.64.8YR 2.0/4.2
Benitoitepale blue0.66roundCalifornia855.6-7.64.4P 8.4/2.0
medium blue1.07roundCalifornia684.527.06.6PB 6.7/6.3
dark blue1.19roundCalifornia468.4-29.17.1PB 4.5/7.0
Beryl
Aquamarinedark blue2.40ovalCoronel Murta Mine, Brazil61-2.7-17.52.8PB 6.0/4.3
dark blue66.53antiqueBrazil38-6.0-8.05.8B 3.7/2.3
dark blue45.40emerald cutBrazil544.0-11.00.5PB 5.3/2.8
medium light blue18.08emerald cutBrazil80-6.9-9.08.2B 7.9/2.7
medium blue21.80pearAfrica65-3.5-18.02.6PB 6.4/4.4
Emeraldpale green0.32roundColombia85-12.02.68.9G 8.4/2.2
light yellow-greenemerald cutColombia55-55.015.06.0G 5.4/10.1
medium green0.88emerald cutChivor Mine, Colombia70-41.72.52.0BG 6.9/8.0
dark blue-green1.35emerald cutMuzo Mine, Colombia46-73.29.18.3G 4.5/13.6
dark greenemerald cutZambia40-60.015.06.0G 3.9/11.0
light blue-green1.96emerald cutNigeria68-23.50.52.7BG 6.7/4.6
Green beryllight green11.25roundBrazil65-3.56.54.3GY 6.4/1.0
light yellow-green18.42triangleBrazil75-5.113.22.0GY 7.4/1.9
greenish-yellow19.09antiqueBrazil70-9.321.13.2GY 6.9/3.2
blue-green4.54emerald cutBrazil68-5.23.12.0G 6.7/1.0
Golden beryldark yellow20.00emerald cutBrazil63-8.239.08.3Y 6.2/5.4
medium yellow32.79antiqueBrazil74-6.034.27.0Y 7.3/4.8
dark orange18.60antiqueBrazil4517.471.79.9YR 4.4/11.5
golden orange18.98pearBrazil61-1.042.04.3Y 6.0/6.0
golden orange40.98ovalBrazil50-0.541.04.5Y 4.9/5.9
medium dark golden orange3.90emerald cutAfrica7010.270.00.2Y 6.9/10.7
Morganitepink17.33squareBrazil814.6-0.92.8RP 8.0/1.1
peach6.92squareBrazil8010.410.09.7R 7.9/2.7
peach9.06ovalBrazil908.911.81.3YR 8.9/2.6
Brazilianiteyellow-green2.00ovalBrazil74-1.917.05.2Y 7.3/2.4
Cassiteritelight brown14.25roundBolivia477.526.69.3YR 4.6/4.3
yellow2.88roundBolivia821.333.01.8Y 8.1/4.9
Calcitedark brown-orange12.55roundBaja, Mexico4123.258.47.3YR 4.0/10.1
GemstoneColorWeightShapeLocationL*a*b*Munsell
Calcite-Codark rose pink3.40cushionSpain2047.4-16.43.1RP 1.9/11.9
Childrenitepeach1.37roundBrazil7419.09.33.8R 7.3/4.5
Chrysoberyl
brownish-green7.80ovalSri Lanka47-3.628.86.7Y 4.6/4.0
medium-brown6.19ovalSri Lanka385.836.31.3Y 3.7/5.4
brownish-yellow7.51roundSri Lanka542.627.71.9Y 5.3/4.1
green-yellow7.04roundSri Lanka54-0.440.44.2Y 5.3/5.8
yellow-brown11.84ovalBrazil672.848.12.3Y 6.6/7.1
dark greenish-yellow13.25antiqueBrazil49-6.036.37.7Y 4.8/5.1
brown9.30emerald cutSri Lanka436.742.51.2Y 4.2/6.5
dark greenish-yellow21.30ovalSri Lanka59-4.931.37.0Y 5.8/4.4
lemon yellow11.49ovalBrazil72-9.430.80.9GY 7.1/4.2
greenish-yellow12.02roundSri Lanka50-7.141.38.0Y 4.9/5.7
Chrysocollamedium blue13.59free formArizona39-36.0-9.55.9BG 3.8/7.4
Cinnabarred1.37fancyCharcas, Mexico1137.436.51.1YR 1.0/9.4
Clinohumiteorange1.52emerald cutUSSR3624.859.07.3YR 3.5/10.3
Corundum
RubyPink-violetish red3.66antiqueThailand2340.9-0.87.5RP 2.2/9.5
dark pinkish-red3.56ovalBurma2448.0-19.32.2RP 2.3/12.3
dark red2.23ovalThailand1944.0-1.37.6RP 1.8/10.2
medium pinkish-red2.30ovalBurma4945.8-21.90.6RP 4.8/12.0
opink-orangy red2.11antiqueThailand2646.22.48.5RP 2.5/10.7
medium red2.07antiqueThailand2445.90.27.9RP 2.3/10.6
violetish-red3.56antiqueThailand1842.5-7.25.4RP 1.7/10.2
violetish-red1.02pearThailand3838.8-19.30.6RP 3.7/10.3
pinkish red0.98ovalThailand3750.5-19.12.2RP 3.6/12.8
Sapphirelight pink2.12ovalSri Lanka2319.6-12.19.1P 2.2/5.1
medium purple- blue3.76antiqueSri Lanka3821.7-40.78.9PB 3.7/10.2
dark green4.25ovalSri Lanka20-11.611.58.2GY 1.9/2.4
fine medium dark blue5.21ovalSri Lanka2123.0-48.27.6PB 2.0/12.1
medium blue6.05ovalSri Lanka479.7-30.97.4PB 4.6/7.3
dark blue2.60ovalSri Lanka1715.5-39.07.0PB 1.6/9.7
violetish-pink4.02ovalSri Lanka3733.7-21.88.5P 3.6/8.9
dark lemon yellow16.12ovalSri Lanka70-0.356.83.8Y 6.9/8.2
medium green1.98antiqueUmba Valley, Tanzania52-5.419.89.3Y 5.1/2.7
very pale yellow1.40antiqueUmba Valley, Tanzania794.75.41.0YR 7.8/1.3
red-violet1.86emerald cutUmba Valley, Tanzania347.2-8.93.1P 3.3/2.5
orangy-yellow3.41antiqueUmba Valley, Tanzania558.338.20.1Y 5.4/6.0
brown-pink3.28emerald cutUmba Valley, Tanzania3615.412.39.5R 3.5/3.7
orangy-red0.96antiqueUmba Valley, Tanzania4044.715.62.8R 3.9/10.5
blue-violet3.77antiqueUmba Valley, Tanzania428.4-19.38.7PB 4.1/4.6
green1.46roundUmba Valley, Tanzania55-9.119.23.5GY 5.4/2.9
powder-blue2.56roundUmba Valley, Tanzania545.4-23.36.9PB 5.3/5.5
brownish-orange4.64antiqueUmba Valley, Tanzania3033.735.61.1YR 2.9/8.9
GemstoneColorWeightShapeLocationL*a*b*Munsell
Heated Geudadark golden yellow6.13ovalSri Lanka8111.678.30.1y 8.0/12.1
medium orange3.89ovalSri Lanka4211.254.60.4Y 4.1/8.4
dark orange4.00ovalSri Lanka5331.592.37.3YR 5.2/15.7
yellow2.21ovalSri Lanka808.078.31.0Y 7.9/11.9
orangy-yellow3.60ovalSri Lanka5811.470.00.7Y 5.7/10.7
Miscellaneousdark blue3.87emerald cutAustrlaia158.7-32.05.7PB 1.4/7.8
dark blue-green5.75emerald cutAustrlaia18-7.1-7.32.5B 1.7/2.2
dark pink6.2ovalSri Lanka5225.8-18.17.7P 5.1/7.0
dark blueKahsmir255.0-25.05.4PB 2.4/6.0
beige-yellow5.55ovalSri Lanka6013.729.96.0YR 5.9/5.4
dark blue2.3pearMontana28-7.3-8.44.0B 2.7/2.5
medium blue1.35octagonMontana40-6.0-13.58.8B 3.9/3.6
medium light blue1.19pearMontana520.9-17.04.8PB 5.1/4.1
light blue1.4shieldMontana772.013.57.0PB 7.6/3.1
blue-green1.47pearMontana48-8.20.71.1BG 4.7/1.5
light yellow-green1.77pearMontana75-8.613.36.1GY 7.4/2.2
light greenish-yellow1.66shieldMontana70-11.925.34.0GY 6.9/3.8
light green1.10octagonMontana64-4.013.30.1GY 6.3/1.8
yellow0.95shieldMontana70-2.026.74.8Y 6.9/3.8
orange-mauve0.96shieldMontana585.85.80.6YR 5.7/1.5
beige1.03pearMontana608.19.51.7YR 5.9/2.2
Creediteviolet0.96emerald cutMexico6015.7-12.66.6P 5.9/4.4
Crocoiteorangy-red1.87emerald cutTasmania3350.075.03.0YR 3.2/15.8
Cupritedark red11.62roundSouth Africa648.527.76.9R 0.9/11.1
Diasporepale gray-yellow2.1emerald cutTurkey69-0.813.84.2Y 6.8/2.0
Diopsidemedium green2.23roundNew York72-3.515.67.6Y 7.1/2.2
     chromedark green0.75roundKenya36-26.251.04.7GY 3.5/8.0
     chromedark green4.95antiqueUSSR10-18.035.73.5GY 0.9/5.5
Dioptasegreen0.41emerald cutTsumeb, Namibia28-62.6-1.21.5BG 2.7/12.0
Enstatitebrown0.52roundBurma523.332.51.9Y 5.1/4.8
green2.43pearAfrica32-20.254.02.4GY 3.1/7.8
light brown4.38emerald cutAfrica5014.840.07.7YR 4.9/6.8
Epidotedark brown3.43cushionAfrica27.321.70.1Y 0.9/3.5
Euclaselight blue- green1.33emerald cutBrazil77-4.60.03.6BG 7.6/0.9
dark blue0.24emerald cutZimbabwe35-4.5-20.40.8PB 3.4/5.0
Fluoriteemerald-green3.05pearColombia59-27.019.10.9G 5.8/5.3
pink0.92roundSwitzerland7018.46.82.0R 6.9/4.4
violet5.75roundIllinois1720.325.11.8P 1.6/7.1
blue-green6.05ovalEngland44-19.87.64.5G 4.3/3.6
yellow8.80roundIllinois620.149.83.8Y 6.1/7.2
blue75.77marquireIllinois36-2.831.32.2PB 3.5/7.6
Garnets
Andraditemedium green0.47roundKorea50-13.233.22.5GY 4.9/4.8
olive green0.51roundKorea470.340.34.2Y 4.6/5.8
brown0.33roundEast Siberia, USSR2915.644.38.9YR 2.8/7.4
Demantoidmedium green0.68emerald cutUSSR51-38.854.67.2GY 5.0//9.8
Grossularmedium orange9.81roundAsbestos, Quebec4414.428.05.9YR 4.3/5.2
light mint green4.15antiqueTanzania70-11.919.65.8GY 6.9/3.2
light brownish-yellow5.01triangleTanzania556.332.90.1Y 5.4/5.1
light brownish-yellow2.59emerald cutTanzania849.438.98.2YR 8.3/6.3
cinnamon brown4.48antiqueTanzania5119.617.910.0R 5.0/5.0
GemstoneColorWeightShapeLocationL*a*b*Munsell
near colorless2.18roundTanzania920.98.40.1Y 9.1/1.3
medium mint green3.88antiqueTanzania58-16.823.06.9GY 5.7/4.1
dark green2.47emerald cutTanzania (tsavorite)50-46.634.60.5G 4.9/9.2
dark orange4.82antiqueTanzania8844.466.00.3YR 8.7/14.7
very pale green4.14antiqueTanzania772.94.63.5YR 7.6/0.9
Malayamedium brownish-orange12.8triangleTanzania3025.624.60.6YR 2.9/6.5
brownish-pink11.39antiqueTanzania4417.35.69.1R 4.3/1.7
orange6.38triangleTanzania4516.930.75.3YR 4.4/5.9
gray-brown8.23antiqueTanzania398.020.68.0YR 3.8/3.5
pinkish-orange8.56antiqueTanzania4819.121.31.3YR 4.7/5.2
dark orange14.46antiqueTanzania2535.948.93.3YR 2.4/10.6
Pyrope
Almandinemedium rose-pink3.09roundSri Lanka2836.71.88.3RP 2.7/8.5
light rose-pink0.74roundNorth Carolina54-24.8-5.73.4RP 5.3/6.0
dark red0.58roundArizona2333.538.42.1YR 2.2/9.0
brown-orange1.27roundMozambique3038.122.06.5R 2.9/8.9
brownish6.48emerald cut?2638.628.48.5R 2.5/9.3
Rhodolitered-violet10.88ovalTanzania1222.5-9.12.3RP 1.1/5.7
brownish-violet13.10roundTanzania1031.77.32.0R 0.9/7.3
fine dark violet24.46antiqueTanzania1637.6-4.86.0RP 1.5/9.0
Spessartinelight orange3.61roundOrissa,India5518.138.35.9YR 5.4/7.0
medium orange3.81roundOrissa,India4529.155.85.2YR 4.4/10.6
dark orange5.65ovalOrissa,India2234.254.24.7YR 2.1/10.8
Spessartinedark brownish-orange4.05pearBrazil2531.131.81.2YR 2.4/8.0
dark brownish-orange15.40emerald cutMadagascar1430.341.44.1YR 1.3/8.8
light orange4.65ovalAmelia, Virginia4028.337.92.8YR 3.9/8.2
medium brownish-orange6.41antique?3137.258.64.1YR 3.0/11.9
dark orange1.27roundAfrica3827.529.61.2YR 3.7/7.3
very dark brownish-orange16.80antiqueBrazil426.526.72.0YR 0.9/6.7
light orange1.75roundRamona, Californnia7434.562.43.1YR 7.3/12.5
Tsavoritemedium dark green4.11ovalTanzania40-49.032.41.0G 3.9/9.4
fine medium green2.47emerald cutTanzania50-46.634.80.5G 4.9/9.2
medium green1.25emerald cutTanzania44-47.227.81.6G 4.3/8.9
dark green4.01ovalTanzania32-51.832.61.1G 3.1/9.8
Haüyneblue0.04fancyGermany521.0-40.04.1PB 5.1/9.7
Hypersthenedark bottle green2.52pearArizona25-6.041.78.1Y 2.4/5.7
Idocrasebrown2.30roundAfrica4614.952.69.2YR 4.5/8.5
green1.05roundAfirca5214.451.51.0GY 5.1/7.1
brown3.82emerald cutSwitzerland3515.942.68.3YR 3.4/7.2
brown1.40cushionItlay516.667.02.4Y 5.0/9.9
Ioliteblue1.56roundIndia2810.7-24.08.2PB 2.7/5.9
blue3.00emerald cutIndia2610.1-25.37.6PB 2.5/6.1
Kornerupinelight green0.40roundAfrica65-32.128.60.1G 6.4/6.7
    (chrome)light brown12.07roundSri Lanka505.430.50.3Y 4.9/4.6
olivy-brown2.62ovalSri Lanka341.019.75.5Y 3.3/2.8
Kyanitemedium blue8.30cushionBrazil48-11.6-21.77.9B 4.7/5.8
dark blue4.01cushionBrazil401.0-33.03.8PB 3.9/8.0
Lazuliteblue0.70roundBrazil47-6.1-31.51.5PB 4.6/7.8
Microlitegreen0.14ovalBrazil59-24.023.39.4GY 5.8/5.1
Manganotantalitered4.85cushionMozambique1137.236.51.2YR 10./9.4
Opalyellow11.74emerald cutIdaho495.559.32.5Y 4.8/8.7
brown-gray5.15roundMexico350.712.73.2Y 3.4/1.8
GemstoneColorWeightShapeLocationL*a*b*Munsell
orangy-red0.76roundMexico4650.995.44.0YR 4.5/18.6
light orange8.04ovalMexico4619.355.78.1YR 4.5/9.5
Peridotmedium green8.25antiqueArizona47-20.952.33.2GY 4.6/7.7
medium green9.20triangleArizona34-11.948.50.1GY 3.3/6.6
light green4.51pearNorway66-19.031.75.9GY 6.5/5.2
light green8.22ovalEgypt58-13.331.93.0GY 5.7/4.7
Phosphophyllitelight blue-green0.81emerald cutBolivia85-4.2-1.49.8BG 8.4/0.9
Proustitedark red2.58roundGermany1851.650.010.0R 1.7/13.5
Quartz
Amethystlilac6.22emerald cutBrazil5719.4-12.08.6P 5.6/5.0
light violet9.18ovalBrazil3718.5-14.57.1P 3.6/5.2
dark violet8.52fancy ovalZambia625.5-26.03.0P 0.9/8.0
medium dark violet4.40ovalBrazil622.8-21.13.9P 0.9/6.9
medium dark violet3.61roundBrazil1229.8-29.03.3P 1.1/9.2
medium dark purple6.41roundBrazil1420.1-23.22.3P 1.3/6.8
dark purple6.38fancy emerald cutBrazil1225.9-25.33.5P 1.1/8.0
“Siberian”14.91ovalPara, Brazil830.8-23.47.8P 0.9/8.5
Citrinemedium yellow-orange7.55roundBrazil5213.543.18.4YR 5.1/7.1
brownish-orange4.20roundBrazil387.934.80.1Y 3.7/5.4
dark straw-yellow8.81ovalBrazil555.423.99.8YR 5.4/3.8
pale straw-yellow12.64ovalBrazil610.719.32.7Y 6.0/2.8
light orange16.90antiqueBrazil5612.161.00.1Y 5.5/9.5
medium orange19.72ovalBrazil5319.266.58.7YR 5.2/10.9
dark orange15.76ovalBrazil3321.751.17.4YR 3.2/8.9
dark orange15.33ovalBrazil2930.561.16.3YR 2.7/11.3
     (“Madeira”)
Green quartzapple green4.48ovalBrazil52-9.513.06.5GY 5.1/2.3
Rose Quartzmedium pink14.2emerald cutBrazil5113.14.22.0R 5.0/3.1
pale pink18.79antiqueBrazil716.06.10.2YR 7.0/1.5
Smoky Quartzmedium brown23.78roundBrazil267.612.35.6YR 2.5/2.4
light brown15.61emerald cutBrazil634.523.70.1Y 6.2/3.7
medium yellow-brown9.37emerald cutBrazil435.622.50.1Y 4.2/3.5
dark brown13.57emerald cutBrazil208.615.16.5YR 1.9/2.8
very dark brown7.49emerald cutBrazil16.811.66.6YR 0.9/2.2
Rhodochrositepink11.88antiqueColorado3940.211.41.8R 3.8/9.4
pink7.15rhomboidPeru5142.111.91.3R 5.0/9.9
orangy-red9.42roundSouth Africa3052.752.310.0R 2.9/14.0
pink3.95roundArgentina4937.615.63.5R 4.8/8.8
red24.60antiqueSouth Africa1643.644.91.2YR 1.5/11.4
Scapolitegold-yellow32.44ovalTanzania673.055.42.5Y 6.6/8.1
gold-yellow32.00antiqueTanzania533.253.73.0Y 5.2/7.9
very pale yellow5.77antiqueBrazil76-1.811.85.9Y 5.2/7.9
lemon yellow9.03antiqueBurma611.037.03.1Y 6.0/5.4
violet4.36ovalTanzania3016.1-16.24.2P 2.9/5.0
Scheelitestraw yellow2.85pearKorea840.030.32.5Y 8.3/4.4
Scoroditeviolet-blue1.15fancyNamibia235.7-13.48.0PB 2.2/3.3
violet-blue1.50pearNamibia155.3-26.84.9PB 1.4/6.6
Sinhalitedark straw-yellow4.58antiqueSri Lanka506.632.50.1Y 4.9/5.1
brown7.07ovalSri Lanka1616.737.68.1YR 1.5/6.5
green4.18ovalSri Lanka471.025.63.2Y 4.6/3.7
yellow9.18ovalSri Lanka658.937.09.1YR 6.4/5.9
Smithsonitepale yellow8.00roundNamibia754.29.05.6YR 7.4/1.6
beige10.40ovalNamibia731.36.09.3YR 7.2/0.9
GemstoneColorWeightShapeLocationL*a*b*Munsell
Sodaliteintense dark blue0.85emerald cutNamibia2320.043.27.7PB 2.2/10.8
Sphaleritelight green1.93roundColorado68-2.873.45.1Y 6.7/10.4
yellow-orange3.30roundSpain726.91002.7Y 7.1/14.7
dark green4.65roundMexico430.655.04.6Y 4.2/7.9
dark orange14.48roundSpain3938.186.66.3YR 3.8/15.5
light orange5.57roundSpain5526.610.32.9R 5.4/6.3
Sphenebrownish yellow-green6.22emerald cutMadagascar492.366.94.0Y 4.8/9.7
light yellow-green1.55roundBaja, Mexico73-10.856.28.1Y 7.2/7.8
light brown1.76roundBaja, Mexico2821.251.07.9YR 2.7/8.9
medium green7.01emerald cutIndia34-17.547.52.3GY 3.3/6.9
emerald green1.01roundBaja, Mexico24-33.334.28.5GY 2.3/7.2
brown1.44roundBaja, Mexico6011.980.41.0Y 5.9/12.3
yellow-green4.22roundIndia51-1.367.85.2Y 5.0/9.6
yellow2.65antiqueIndia79-5.874.95.7Y 7.8/10.5
Spinel
Bluesdark blue8.35ovalSri Lanka12-0.6-12.72.1PB 1.1/3.1
medium dark blue9.20ovalSri Lanka15-6.9-12.76.2B 1.4/3.3
light blue9.30ovalSri Lanka31-6.6-11.97.2B 3.0/3.2
lavender-blue15.22ovalSri Lanka504.8-16.87.5PB 4.9/3.9
greenish-blue4.78roundSri Lanka21-13.6-11.10.7B 2.0/3.8
cobalt-blue11.23emerald cutSri Lanka6-2.3-19.70.8PB 0.9/4.8
slightly violetish-blue7.27roundSri Lanka292.8-20.84.8PB 2.8/5.1
dark violet5.46antiqueSri Lanka135.2-13.77.2PB 1.2/3.4
magenta3.96ovalSri Lanka1944.4-4.56.3RP 1.8/10.6
medium purple11.98antiqueSri Lanka147.2-9.22.0P 1.3/2.5
blue-violet8.53ovalSri Lanka256.0-12.68.6PB 2.4/3.1
;ight purple7.98ovalSri Lanka2714.4-9.09.0P 2.6/3.7
gray-blue14.96antiqueSri Lanka30-5.1-8.56.9B 2.9/2.3
Pinksdark rose-red8.21roundSri Lanka1427.02.49.3RP 1.3/6.3
light rose-red7.65ovalSri Lanka3025.3-0.77.1RP2.9/5.8
dark pink5.23ovalBurma24-24.8-4.84.7RP 2.3/6.0
dark violetish-red9.02ovalSri Lanka2119.3-2.25.9RP 2.0/4.6
medium reddish-purple7.07ovalSri Lanka2627.1-6.83.9RP 2.5/6.6
grayish-pink5.89ovalSri Lanka4721.42.08.1RP 4.6/4.9
medium pink6.56ovalUSSR6841.63.87.4RP 6.7/9.7
slightly bluish-pink8.87ovalSri Lanka4215.4-2.54.5RP 4.1/3.7
light dusty -pink11.4antiqueBurma5416.2-2.84.1RP 5.3/3.9
Redsdark orangy-red5.30roundBurma2724.720.710.0R 2.6/6.0
medium pinkish-orange2.98ovalBurma4143.510.40.9R 4.0/10.3
medium brownish-pink3.07roundBurma4234.57.80.7R 4.1/8.2
medium brown2.34roundBurma4526.414.45.7R 4.4/6.2
light brownish-pink10.98ovalBurma4823.68.12.4R 4.7/5.5
dark grayish-pink3.95roundBurma3114.74.12.0R 3.0/3.4
dark red8.89ovalBurma836.831.80.2YR 0.9/9.1
medium red2.68ovalBurma3041.525.16.8R 2.9/9.7
medium pinkish-red3.21roundBurma2747.57.40.1R 2.5/11.1
Spodumeneblue29.85ovalBrazil53-2.7-3.46.7B 5.2/1.0
medium pink16.06emerald cutAfghanistan59-17.712.92.3B 5.8/4.8
medium pink17.76ovalCalifornia5819.1-10.99.1P 5.7/4.8
yellow-green17.01emerald cutAfghanistan63-5.328.07.5Y 6.2/3.9
dark pink47.33ovalBrazil6532.2-19.08.7P 6.4/8.3
GemstoneColorWeightShapeLocationL*a*b*Munsell
Taaffeitegray-mauve1.60rhomboidSri Lanka504.50.89.0RP 4.9/1.0
Topazyellow-brown6.72roundUSSR3813.037.28.6YR 3.7/6.2
red-orange12.59emerald cutBrazil4938.637.59.9R 4.8/10.1
dark beige5.29roundMexico5612.026.36.2YR 5.5/4.8
yellow4.65ovalBrazil598.627.78.3YR 5.8/4.6
dark orange25.25ovalBrazil6123.961.56.6YR 6.0/10.8
brownish-pink8.76antiqueBrazil6335.05.78.6RP 6.2/8.2
medium blue7.2ovalBrazil60-14.3-17.66.1B 5.9/5.2
red-orange8.45antiqueBrazil6534.426.87.6R 6.4/8.7
medium pink17.84ovalUSSR7325.2-16.97.7P 7.2/6.7
Tourmaline
Rubellitepinkish-orange36.85emerald cutMadagacar2538.321.26.4R 2.4/8.9
dark red-violet13.16ovalBrazil2447.8-0.97.6RP 2.3/11.1
very dark violet-red17.13emerald cutBrazil528.02.89.6RP 0.9/6.5
medium violet16.73antiqueBrazil2038.1-5.05.8RP 1.9/9.1
dark red10.26antiqueOuro Fino, Brazil1239.57.40.1R 1.1/9.1
dark pinkish-red36.56emerald cutBrazil1941.810.42.0R  1.8/9.7
Blues and Greensintense smalt blue9.84emerald cutBrazil41-21.018.89.6GY 4.0/4.3
blue-green15.96emerald cutBrazil50-40.1-0.12.3BG 4.9/7.7
fine green10.05triangleAfrica3030.723.90.1G 2.9/6.0
   (chrome)
slightly yellowish-green9.68emerald cutBrazil52-39.715.93.9G 5.1/7.3
dark green14.75emerald cutBrazil32-38.831.10.1G 3.1/7.7
Orangy Colorspeachy-orange10.90roundMozambique4231.120.57.2R 4.1/7.4
medium brownish-orange5.74antiqueTanzania4318.656.68.5YR 4.2/9.4
dark brownish-orange4.84roundTanzania4820.970.48.7YR 4.7/11.6
medium orangy-brown10.39ovalTanzania2810.746.00.4Y 2.7/7.1
medium pinkish-brown46.84ovalTanzania3124.026.41.8YR 3.0/6.4
Pinksmedium pink32.32ovalAfghanistan5734.70.06.5RP 5.6/8.2
medium dark rose-pink10.95roundBrazil2834.0-4.25.6RP 2.7/8.1
slightly brownish-pink11.13antiqueMozambique4428.712.54.1R 4.3/6.6
brown-pink21.22emerald cutStewart Mine, Pala California3818.720.61.7YR 3.7/5.0
Mozambiquemedium pinkish-beige2.51roundMozambique6623.77.71.4R 6.5/5.6
Color Suitelight pinkish-beige2.37roundMozambique7819.15.50.4R 7.7/5.6
near colorless2.59roundMozambique857.93.93.5R 8.4/1.9
light pink2.19roundMozambique5633.2-5.74.1RP 5.5/8.0
dark rose-pink2.15roundMozambique3547.0-11.63.9RP 3.4/11.5
dark green2.16roundMozambique24-12.822.04.6GY 2.3/3/5
dark brownish-green2.34roundMozambique34-14.737.02.4GY 3.3/5.4
medium green2.68roundMozambique52-8.341.48.5Y 5.1/5.7
lime green2.10roundMozambique64-8.626.01.2GY 6.3/3.7
very pale green3.08roundMozambique690.112.82.9Y 6.8/1.8
colorless2.22roundMozambique841.52.12.3YR 8.3/0.4
beige-yellow2.04roundMozambique873.821.69.3YR 8.6/3.4
light brown2.33roundMozambique379.051.11.2Y 3.6/7.8
dark brown1.81roundMozambique3618.933.85.6YR 3.5/6.4
blue2.30roundMozambique45-8.4-2.16.2BG 4.4/1.7
GemstoneColorWeightShapeLocationL*a*b*Munsell
Willemitegolden yellow2.35pearFranklin, New Jersey85-7.463.06.2Y 8.4/8.9
Wulfeniteyellow6.11ovalNamibia631.029.02.8Y 6.2/4.2
orangy-red2.54emerald cutRed Cloud Mine, Arizona4543.896.15.4YR 4.4/17.6
Zirconreddish-brown19.03ovalSri Lanka1716.216.72.2YR 1.6/4.1
brownish-yellow17.43ovalSri Lanka3712.249.60.1Y 3.6/7.8
violet-rose14.20roundSri Lanka2030.93.49.4RP 1.9/7.2
dark orange9.26ovalSri Lanka3325.566.07.9YR 3.2/11.4
green4.36ovalSri Lanka48-15.425.85.4GY 4.7/4.2
rose-red11.26emerald cutSri Lanka1926.28.33.1R 1.8/5.9
lemon yellow15.70ovalSri Lanka50-0.331.64.2Y 4.9/4.5
medium blue5.56ovalCambodia46-12.3-14.14.9B 4.5/4.2
yellow8.92ovalSri Lanka6510.858.10.1Y 6.4/9.0
pale gray-green16.63antiqueSri Lanka667.814.65.4YR 5.4/2.7
reddish-brown7.77ovalSri Lanka2623.029.13.2YR 3.5/6.5
light olive green5.34roundSri Lanka47-0.319.24.3Y 4.6/2.7
dark blue2.87roundCambodia56-8.4-11.16.8B 5.5/3.3
light pink1.36roundSri Lanka7111.9-5.80.7B 7.0/2.8
light orange1.44roundSri Lanka5926.258.15.7YR 5.8/10.6
medium orange2.59roundSri Lanka5239.470.94.0YR 5.1/13.9
pale blue-green2.67roundCambodia77-6.9-1.47.2BG 7.6/1.4
Zoisiteviolet-blue26.54pearTanzania2055.0-76.38.6PB 1.9/20.9
light blue-gray1.06roundTanzania750.70.69.5R 7.4/0.1
medium blue2.3roundTanzania603.5-20.76.4PB 5.9/4.8
violet-blue0.96emerald cutTanzania4716.8-35.78.8PB 4.6/8.7
brown-blue0.92emerald cutTanzania617.1-11.72.0P 6.0/3.0

Editor’s Note: The IGS gratefully acknowledges the above as the work of Dr. Joel Arem. We are deeply grateful to him for allowing us to re-purpose this content with attribution.

About the author
Joel E. Arem, Ph.D., FGA
Dr. Joel E. Arem has more than 60 years of experience in the world of gems and minerals. After obtaining his Ph.D. in Mineralogy from Harvard University, he has published numerous books that are still among the most widely used references and guidebooks on crystals, gems and minerals in the world.Co-founder and President of numerous organizations, Dr. Arem has enjoyed a lifelong career in mineralogy and gemology. He has been a Smithsonian scientist and Curator, a consultant to many well-known companies and institutions, and a prolific author and speaker. Although his main activities have been as a gem cutter and dealer, his focus has always been education.
All articles by this author