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Colored gemstones and the assessment of the quality of colored gemstones



The world of minerals is above all a world of colors. No color that doesn't exist. It is all the more difficult to objectively assess the quality of colored minerals, especially colored gemstones.



Table of contents colored gemstones


Definition of colored gemstone

A gemstone is defined by three characteristics:

Based on the gemstone definition, colored gemstones are gemstones or minerals that are not white but colored, meet the criterion of gemstone hardness, have a high degree of purity and are comparatively rare - i.e. not every colored mineral is automatically a colored gem.


Colored gemstones - our recommendation *



Colored gemstone - semi-precious stone - gem stone: similarities and differences

Until a few years ago, minerals were divided into precious and semi-precious stones.

In the meantime, the term semi-precious stones has been replaced by gemstones in order to avoid the negative and value-reducing image of the term semi-precious stone.

Gemstones stand out in comparison to real gemstones by a lower hardness out.

All known minerals in the world are sorted according to ten degrees of hardness, the Mohs hardness. Mohs hardness 1 minerals are very soft. With increasing numbering, the minerals get harder and harder. The diamond with a Mohs hardness of 10 is considered the hardest mineral on earth.

According to the Mohs hardness, minerals of hardness 1 and 2 are considered soft minerals.
The representatives of the Mohs hardness 3 to 5 are classified as medium-hard minerals.
Minerals with a Mohs hardness of 6 or more are referred to as hard minerals and minerals with a Mohs hardness of 7 are very hard minerals that carry the predicate gemstone hardness.

Furthermore, gemstones are characterized by a lower purity. "Impurities" in the form of inclusions "of other minerals, gas bubbles or other faults and cracks in the crystal reduce the value of these minerals. Nonetheless, gemstones can also have "disruptive" inclusions, which are reflected in the price.


Quality criteria of colored gemstones

Evaluating colored gemstones is a challenge.
Unlike diamonds, there is no uniform, officially recognized principle, according to which the quality of colored gemstones can be assessed objectively and internationally.

It looks different with diamonds. The 4C was created in the 20th century especially for the hardest mineral on earth. Criteria that were selected by the Gemological Institute of America (GIA) ** in order to be able to create a detailed expertise based on objective, consistent standards that apply across national borders.
Specifically, the 4C are based on the following criteria

  • C.olour / Color - color of diamonds
  • C.ut - cut of the diamond
  • C.larity - purity of the diamond
  • C.arat - carat / weight of the diamond

All four criteria were broken down precisely and given special names or coded. Even the smallest inclusion in the stone is recorded, every finest shade of color deviating from the extremely fine white of the diamonds is documented and specified in the expert report on the diamond (further information on this: 4C - quality criteria for evaluating diamonds).

There is no such key for colored gemstones. Nevertheless, colored minerals are evaluated according to a comparable principle and the same criteria are used to assess the quality.


Quality feature: the color of colored gemstones

The color is the most important property of colored gemstones.

The natural color of minerals is unique. Even if you can determine the main color and subtle nuances, the exact color is difficult to categorize.

This is easier with minerals that have been subsequently subjected to a color treatment. The artificially created colors are more or less uniform and standardized.

For this reason, when it comes to the color of colored gemstones, importance is attached to the hue and its intensity placed.
Is the color saturated and strong or pale and pastel? When evaluating the color quality of colored gemstones, there is also the question of whether the color evenly is distributed in the stone.

Every now and then, minerals have an uneven color distribution, and sometimes they are faint and deeply tinted at the same time. This flaw can be corrected and compensated for by careful, expert heating, known as burning.

This notice must be given when selling; this often happens in the form of e.g. "Amethyst burnt".


Quality feature: The cut of colored gemstones

Nowadays gemstones are used as both ground by hand as well as by laser and both man and machine can help ensure that the cut is perfect and flawless or shows faults.

Therefore, when assessing the quality of the cut, a closer look is taken to see whether the Proportion harmonious are to each other, the facets are not "cut" or superimposed by other facets and around which Sand it yourself in general acts. For example, a cabochon cut is much more complex than a facet cut (e.g. brilliant cut, Asscher cut or the emerald cut).


Quality mark: The purity of colored gemstones

Regarding the purity of colored gemstones, the GIA has introduced an international system called three types of gem purity differs.

When evaluating possible inclusions, in addition to the Number of impurities or inclusions also theirs size considered and the Influence on the overall impression the purity of the stone.

In some cases, an ingenious cut and the position of the gemstone in a setting can make a mistake virtually invisible. The inclusion of a rutile needle is less noticeable when it is covered by a prong than when the blemish is present in the center of the mineral. Just like multi-faceted cuts with large table facets in the center of a stone present inclusions more than cuts that rely on many, smaller facets.

According to the GIA are Type 1 gemstones those stones with the highest puritywhere neither impurities nor inclusions are visible.
Type 2 gemstones point noticeable inclusions and impurities on that at Type 3 gemstones at the most clearly perceptible are.

However, compromises have to be made with the GIA system, because not all inclusions have a negative effect on the value of a gemstone. In the case of some minerals, impurities or inclusions are desired, as these produce attractive effects, such as asterism - the star effect that is particularly common with sapphires and rubies (star sapphire, star ruby).


Quality feature: the weight of colored gemstones

The following does not always apply to gemstones: the more weight a stone weighs, the more it is worth. A cut colored gemstone is often higher in price than an unworked, unpolished rough stone.

Even when editing Often more than half of the starting weight of a mineral is lost, the skillful cut makes up for this loss. The share of the cut in the price formation of a gemstone is up to 60%.


Quality feature: the hardness of colored gemstones

Sometimes the hardness of the stones is evaluated in addition to the criteria already mentioned, because the boundary between colored gemstones and gemstones is becoming increasingly blurred.
Minerals with a hardness less than 7 are increasingly classified as colored gemstones because of their colors or their beauty. It is also possible that for minerals with a Mohs hardness between 6.5 and 7, the higher Mohs hardness is given in favor of the gemstone definition.


Mineral Mohs hardness 6.5 Mineral Mohs hardness over 7
Kunzite Almandine (garnet)
Peridot Morganite
Tanzanite Painite
Calcite Bixbit
Rhodochrosite Spinel
Roselith Rock crystal
Azurite amethyst
malachite Tiger eye
opal Zircon
Lapis lazuli Tourmaline
Hematitetopaz
agate emerald
Sodalite ruby
Orthoclase sapphire
Prehnite Aquamarine

Table: List of colored gemstones and semi-precious stones and their Mohs hardness (list is not exhaustive).


A-AA-AAA system

In the gemstone and jewelry market, stones are repeatedly offered that are called AAA tanzanite, AAA emerald, AAA opal, AAA morganite, AAA tsavorite, AAA kunzite or AAA amethyst.

This formulation is a system that tries to standardize the quality of colored gemstones. There are no general parameters. Rather, I orient the dealers to the Color as well as purity and give a subjective opinion to the stone. Another gemstone appraiser would possibly classify the rated colored gemstone differently.

Despite international use, the A-AA-AAA system is not recognized everywhere. The reason: The Standards are not defined.

A ranking of quality is hidden behind the letters.

A colored gemstones are of high quality, the quality of AA colored gemstones is even higher and AAA or triple A colored gemstones are colored gemstones of the highest quality.

The difference between A-AA-AAA colored gemstones becomes clear when the stones are placed next to each other and compared with each other.
For example, the green of an A-emerald is washed out and light. The stone appears cloudy and the play of colors is missing. AAA emeralds, on the other hand, are crystal clear, radiant and bright deep green - like from a picture book.

The majority (50 to 75%) of the colored gemstones offered in the trade correspond to the A-grade. 20 to 30% of all colored gemstones have AA status and only ten percent of all colored gemstones receive the AAA rating.


Also interesting:
⇒ Zirconia - imitation gemstones, artificial crystals and gemstones
⇒ Fancy diamonds - colored diamonds
⇒ The most expensive gemstones in the world


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Last updated: April 22, 2020

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