Grading and Evaluation
Gem qualities & Treatment of Gems
Myanmar - Rubies
Rubies are the best
Sri Lanka - Sapphire
Columbia - Emerald
South Africa - Diamond
Characteristics and classification
The traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious; similar distinctions are made in other cultures. In modern use, the precious stones are emerald, ruby, sapphire and diamond, with all other gemstones being semi-precious. This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8 to 10 on the Mohs scale. Other stones are classified by their color, translucency, and hardness. The traditional distinction does not necessarily reflect modern values; for example, while garnets are relatively inexpensive, a green garnet called tsavorite can be far more valuable than a mid-quality emerald. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms ‘precious’ and ‘semi-precious’ in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not necessarily the case.
In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminologyspecific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al2O3). Many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example, diamonds, which have a cubic crystal system, are often found as octahedrons.
Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow), and morganite (pink), which are all varieties of the mineral species beryl.
Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture and luster. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.
Material or flaws within a stone may be present as inclusions.
Gemstones may also be classified in terms of their “water”. This is a recognized grading of the gem’s luster, transparency, or “brilliance”. Very transparent gems are considered “first water”, while “second” or “third water” gems are those of a lesser transparency.
Chemical Name Carbon Formula C| Colors
all colors | Structure Cubic | Hardness 10 |
Specific Gravity (Dichte) 3.4-3.5 | Refractive Index 2.42 | Luster Adamantine |
With exceptional beauty, luster, and sparkle, diamond is the most
iconic of all precious stones and highly prized world wide. However, there are also other uses. Industrial diamond is a essential component in oil drilling, specialized scalpels, tool manufacturing, and other industries, all of which use the supreme hardness of diamonds for cutting tools and abrasive powders.
For over 2,000 years, diamonds were found only as crystals in rivers. Until 1725, India was the major source. As Indian production dropped, diamonds were found in Brazil, and in 1867 they were found in river beds near the Orange River in
the Kimberley region of South Africa. Further exploration there revealed volcanic pipes of a previously unknown rock type containing diamonds; this was named kimberlite and was recognized as the diamond source rock. Its discovery formed the foundation of the modern diamond industry. Many similar pipes have since been found in different African
countries, Siberia, Australia, and more recently in Canada, China, and the US.
Induces purity and fearlessness.
Gives artistic abilities and worldly happiness.
Strengthens bones and is useful for diseases of
the sex organs. Makes one more attractive.
Ruling Planet Venus | Nature of Gem Hot | Finger to be worn Ring finger | Preferred Metal Gold or Platinum
Chemical name Aluminium oxide | Formula Al203 |
Color Red | Structure Trigonal | Hardness 9 | SG
4.0-4.1 | RI 1.76-1.78 | Luster Vitreous | Streak Colorless |
Locations Myanmar, Sri Lanka, Nigeria, Thailand, Australia, Brazil, Kashmir, Cambodia, Kenya, Malawi, Colombia, US, and more
Ruby is the red version of the mineral corundum, and its color seamlessly picks up where pink sapphire ends. Only darker stones are generally called rubies, but the difference between ruby and pink sapphire can be a matter of opinion. Ruby is sometimes tinged with purple, and the most valued hue is known as pigeon-blood red. It has been mined from the gravels of Sri Lanka since at least the 8th century BC, the subject of speculation from its earliest days. Ancient Hindu and Burmese miners considered pale pink sapphires were unripe rubies.
RUBY is the precious stone that occurs as a red
transparent variety of the mineral corundum. It is symbolic of excellent health, vigor, love and
passion, an aid to firm friendship, and believe
to ensure beauty. It strengthens the heart and
blood circulation, makes one bold and courageous
and eliminates depression, sadness or sensuality,
increase name and fame. Its color ranges from
purplish red (called Pigeon Blood) or bluish red
to a yellowish red. When cut into a cabochon (a
non-convex) form, some specimens of ruby
exhibit asterism i.e. a six-rayed star can be seen
in the interior of the stone. These are called star
rubiesi3 and are very highly prized, Burmese
rubies are considered the finest. The ruby is a very
brilliant, hard, durable, and wearable stone.
Ruling Planet Sun | Nature of Gem Hot | Finger to be worn Ring finger | Preferred Metal Gold | Remark Passion under control
Chemical Name Aluminium oxide | Formula Al203
Colors Most colors | Structure Hexagonal, trigonal
Luster Adamantine to vitreous |
Hardness 9 SG 4.0-4.1 |RI 1.76-1.77 | Streak Colorless
Ruby and sapphire are gem varieties of the same mineral, corundum, an aluminium oxide that is second to diamond in hardness. Although commonly known of as blue, sapphire can also be found colorless, green, yellow, orange, violet, and pink, among other hues. Before the 19th century, when geologists realized that sapphires of all colors were the same mineral, naming of the gem persisted from medieval times: green sapphire was called Oriental peridot and yellow sapphire was Oriental topaz.
With three exceptions, modern gemologists simply use the word “sapphire” preceded by the color ot the stone: for example, yellow sapphire or green sapphire. Two exceptions are the rare pink-orange stones that are called padparadscha (Sanskrit for “lotus blossom”), and sapphire that shines blue in daylight and reddish
or violet in electrical light, which is called alexandrine or alexandrite sapphire.
BLUE SAPPHIRE The finest blue sapphires are
from Burma and Kashmir. It counteracts
enviousness from others and removes the evil eye
thereby protecting from travel dangers and mental
unrest and various forms of madness. It alleviates long-term misfortunes by causing a change
of place/ residence. Fine, brilliant, deep blue
Burmese sapphires will surely dazzle the eye.
Ruling Planet Saturn | Nature of Gem Very Cold | Finger to be worn middle or pinky finger | Preferred Metal Gold
Chemical Name Aluminum beryllium silicate |Formula
BegA|(Si03)6 | Colors Emerald green to green, yellow green
to blue | Structure Hexagonal | Hardness 7.5-8 | SG
27-2.8| RI 1.565-1.602 | Luster Vitreous| Streak White
Locations Colombia, Zambia, Brazil, Zimbabwe
One of the most expensive gemstones, emeralds are the rich green version of beryl, the mineral found in igneous, metamorphic, and sedimentary rocks. Most emeralds have many inclusions and internal flaws, and these imperfections are unique to each stone. For common use, the brittle gem is usually faceted in its signature emerald cut. This is a step, or trap, cut, which combines a reciangular shape with shortened corner facets, maximizing the emerald’s unique green color, and protecting it from external destruction and internal stress.
EMERALD is the green variety of the mineral
beryl making its wearer faithful & of fixed
commitments. It helps in planning & forecasting
by enhancing intuition & psychic powers. It
sharpens the intellect and gives a photogenic
memory thereby improving learning ability,
communication and clairvoyance. Good for
general health, particularly the nervous system,
it also has the power of healing diseases of the
eye. It has the color of fresh young green grass as in the world’s fines: “drop of oil” emerald from
‘Colombia. Although a hard stone, emerald wi
chip easily since it tends to be somewhat britle
so special care should be given in wearing and
handling. A common flaw reduction technique
is to boll the emerald in oil (sometimes tinter
green) and is actually good for the stone in light
er its fragile nature. Oiling hides some of ine
Whitish flaws (cracks) by tilling the cracks and
becomes an integral part of the emerald unlessi
is subjected to some type of degreasing procedure
Ruling Planet Mercury | Nature of Gem Cold | Finger to be worn pinky or middle finger | Preferred Metal Gold | Remark Not for newly married couples
The grading and evaluation of gems can begin even before they are removed from the ground. Within some gem deposits, certain areas are known to yield more or better-quality gem material, and are thus mined first. Only a small percentage of what is recovered is actually of gem quality, and this is further sorted to separate out the gem materlal. Any gem-quality roughs found are then carefully evaluated for color, clarity and size. Even much of this selected matenal may remain uncut if it is too small, oddly shaped, or tor some reason does not fit the current market demand. Cutting is expensive and time-consuming, and so meticulous grading at this early stage is essential. To be certain, the cutter will make his or her final decision about what is cut, but the greater the evaluation and, grading before gems reach the cutter’s workshop, the better.
In general, intensely colored natural diamonds command very high prices. However, “colorless diamonds, because they have a generally higher value than most “colored” stones, are graded by a more complex system. A single change in grade can result in a large difference in value. To avoid the large value changes between the grades that would occur if there were only a few grades, there are numerous grades based on each of the four “Cs” thus keeping the changes in value relatively small. The grades and their determinates below are those of the Geological Institute of America (GIA).
In 1952, Richard T. Liddicoat, along with Marquis Person, Joe Phillips, Robert Crowningshield and Bert Krashes began to work on a new diamond grading system which they called the “diamond grading and evaluation appraisal”. In 1953, they released their new system which assessed three aspects of diamonds; make, color and clarity. They took terminology used in the industry at the time and refined the definitions to produce a clarity scale by which diamonds could be consistently graded. The system at that time contained nine grades: Flawless, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, and I2. The ‘I’ of the I1, and I2 grades originally stood for “Imperfect”.
During the 1970s, two changes were made to the system. Firstly, the Internally Flawless grade was added, as GIA noticed that many diamonds were being aggressively cut to remove any surface blemishes, and thereby reducing the cutting quality (“make”) of the diamonds. The Internally Flawless grade gave diamond manufacturers a choice to leave blemishes on the surface of the stone, and achieve a grade higher than VVS1. The second change made to the grading system was the introduction of the I3 grade. This change was made in response to a growing number of diamonds of very low clarity being cut.
The last change to the clarity grading system took place in the 1990s when the term “imperfect” was changed to “included”.
Modern GIA grading System
|Very Very Slightly Included
|Very Slightly Included
The GIA diamond grading scale is divided into six categories and eleven grades. The clarity categories and grades are:
- Flawless category (FL) diamonds have no inclusions or blemishes visible under 10x magnification.
- Internally Flawless category (IF) diamonds have no inclusions visible under 10x magnification, only small blemishes on the diamond surface.
- Very, Very Slightly Included category (VVS) diamonds have minute inclusions that are difficult for a skilled grader to see under 10x magnification. The VVS category is divided into two grades; VVS1 denotes a higher clarity grade than VVS2. Pinpoints and needles set the grade at VVS.
- Very Slightly Included category (VS) diamonds have minor inclusions that are difficult to somewhat easy for a trained grader to see when viewed under 10x magnification. The VS category is divided into two grades; VS1 denotes a higher clarity grade than VS2. Typically the inclusions in VS diamonds are invisible without magnification; however, infrequently some VS2 inclusions may still be visible. An example would be on a large emerald cut diamond which has a small inclusion under the corner of the table.
- Slightly Included category (SI) diamonds have noticeable inclusions that are easy, or very easy for a trained grader to see when viewed under 10x magnification. The SI category is divided into two grades; SI1 denotes a higher clarity grade than SI2. These may or may not be noticeable to the naked eye.
- Included category (I) diamonds have obvious inclusions that are clearly visible to a trained grader under 10x magnification. Included diamonds have inclusions that are usually visible without magnification or have inclusions that threaten the durability of the stone. The I category is divided into three grades; I1 denotes a higher clarity grade than I2, which in turn is higher than I3. Inclusions in I1 diamonds often are seen by the unaided eye. I2 inclusions are easily seen, while I3 diamonds have large and extremely easy to see inclusions that typically impact the brilliance of the diamond, as well as having inclusions that are often likely to threaten the structure of the diamond.
GIA clarity grading procedure
GIA clarity grading is performed under 10x magnification with darkfield illumination. The GIA Laboratory uses as standard equipment binocular stereo microscopes which are able to zoom to higher magnifications. These microscopes are equipped with darkfield illumination, as well as an ultraviolet filtered overhead light. When grading is performed using a 10x handheld loupe, darkfield illumination is more difficult to achieve. The grader must use a light source in such a way that the base of the stone is lit from the side, and the crown of the stone is shielded from the light.
After thoroughly cleaning the diamond, the diamond is picked up using tweezers in a girdle-to-girdle hold. The grader views the diamond for the first time through the table, studying the culet area of the stone for inclusions. The diamond is then set down and picked up with the tweezers in a table-to-culet hold. In this position, the diamond can be studied from the pavilion side, and the crown side, examining the diamond through each facet for inclusions. Once a sector of the diamond has been thoroughly examined, the grader rotates the diamond in the tweezer, so that the neighboring sector can be examined. The grader uses darkfield lighting to reveal characteristics, and alternates to reflected, overhead lighting to ascertain whether a characteristic lies within the stone, on the stones surface, or both. If the grader is using a stereo microscope, they may zoom in to a higher magnification to make closer observations of an inclusion, but then return to 10x magnification to make an assessment of its impact on the clarity grade.Grad
If a stereo binocular microscope has been used, a final assessment using a 10x loupe is performed before the final judgment is made on the clarity of the stone. The grader first decides the clarity category of the diamond: none (FL, or IF for a blemish), minute (VVS), minor (VS), noticeable (SI), or obvious (I). The decision is then made on the grade of the diamond.
Gemstones of Type I level are usually “eye clean” as definition, with no visible inclusions. stones in this section are usually of such high clarity that they will be free of even minor inclusions. For lapidaries, collectors, and jewelers, these stones represent the height of desirability.
Gems of the Type II category typically display some inclusions that are visible to the naked eye but do not detract from the desirability and overall beauty of the gemstone. Many such stones with visible inclusions are faceted for use in jewelry.
Tourmaline: all except red, green and watermelon
Zircon, all except blue
The Type III classification is mainly applied to gemstones that feature obvious inclusions
or other imperfections. However, even stones with prominent inclusions are regularly cut for use in jewelry, and are considered beautiful
objects in ther own right.