Coloured Gemstone Guide

Welcome to the  Coloured Gemstone Travel Guide

As with diamonds, coloured gemstone quality and value are assessed according to
the "Four Cs": colour, carat weight, clarity, and cut.
When purchasing, always remember the 4 C's and you will fare right.

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Colour is the number one factor in the value of any gemstone. coloured gemstone would not have colour without the presence of impurities in its crystal structure. As a result, virtually every gemstone that shows a nice colour may have inclusions. Examples are emerald, pink tourmaline, and ruby.

The most important consideration when shopping for a coloured stone will be...colour. When shopping for coloured gemstones it will be important that you view the stone from all directions. The more valuable gemstones will have colours that are uniform in all directions with no dark or light bands of colour, nor any zones of darker or lighter colour. This uniformity of colour should be very important with your shopping. A gemstone that shows marked areas of darker or lighter colours should be priced lower than gemstones with even colour saturation.

Always remember that colour is the most important consideration when coloured gemstone shopping. Don't turn down a gemstone showing nice colour simply because of a minor cutting error or some inclusions that you can see. colour is the most important factor and should out weigh all other grading factors as long as the beauty of the stone is not affected.

When shopping for a coloured gemstone you should be aware of the level of acceptable clarity that the particular gemstone will offer. Some stones, for instance emerald and pink tourmaline, will almost all have some type of inclusions. While others, such as amethyst and green tourmaline, should generally be free of inclusions. As you read the individual sections on the gemstones you will learn the acceptable levels of clarity per stone.

A common misperception in judging gems is people assume that the darker the colour, the better the stone. That isn't true: colour can be too dark, as with some sapphires that look more black than blue. If a gem's colour is too dark, it is subdued and lifeless. A much better rule of thumb is the brighter and more rich and vivid the colour the better. In general, within each gemstone variety, a clear, medium-tone, very intense and saturated basic colour is the most preferred. Muted colours or colours between hues, which some might find very attractive, are usually less expensive. Look at the colour in different kinds of light, since the light spectrum can affect colour grealty. 

Carat Weight

All gemstones are sold by their weight. This is measured in carats. But exactly why is it called a carat? Actually the word Carat is derived from carob, the bean that is often used as a chocolate substitute. Carob trees grow in the Mediterranean region, and in ancient times a diamond of one carat, or carob, was equal in weight to a single bean, or seed, of the carob tree. In the Far East, rice was used--- four grains equaled one carob bean. Eventually the carat was standardized at 200 milligrams (1/5 of a gram), and the grain was standardized at 50 milligrams. Sometimes you will hear a diamond dealer refer to a one-carat diamond as a four grainer.

Any gemstone that you are considering for purchase should be marked with its carat weight. Simply buying gemstones by the millimeter size is popular in some stores but it does not give you an accurate representation of the size of the stone you are buying. Whenever you purchase a gemstone make sure that you receive, in writing, the proper carat weight of the stone.

The term "points" means a decimal fraction of a carat. One carat equals 100 points, so a 75-point gemstone would weigh 3/4 of one carat. Please see details about size to carat and gram weight here.


Gemstone clarity will affect value at different levels in different gemstones. In diamonds, even the smallest inclusion can result in a significantly lower price than a stone without the inclusion. In coloured gemstones, however, the matter of a small inclusion is generally not regarded as important in most stones. In fact, some gemstones will be viewed with a great deal of suspicion without the presence of at least some inclusions. Examples are emerald, ruby, peridot, sapphire, and garnet.

An inclusion is any object within a stone that is not part of the original crystal structure of the gemstone. These can be other crystals that were caught in the gemstone as it grew, gas and/or air bubbles, or even bits of non-crystallized material. The important thing to remember here is that gemstones have colour directly as the result of impurities in their crystal structure. And since most of these impurities show themselves as inclusions in coloured stones, you should always remember that virtually all coloured gemstones will naturally have inclusions.

In summary, Clarity is the term used to describe how clean a gemstone is using a monochromatic colour corrected 10X magnification. The Gemological Institute of America (GIA) has set forth standards for clarity grading of coloured Gemstones and Diamond. 


This term is used to describe how well a gemstone is cut. A well cut gemstone, both diamond and coloured stone, should be cut in such a manner to present the stone's best colour and brilliance to its wearer. Often, since gemstones are sold by weight, many cutters will cut a stone is such a manner to keep the most weight instead of the most beauty. This will show itself in uneven facets, bulging sides, or colours that do not appear to show the best when viewed through the table of the stone. You can even see right through some stones because they have been cut in such a manner that leaves a window in the stone.

A good cut is determined by the stones light-reflecting properties and its light dispersion. This is the fire, brilliance, and personality the diamond projects to the wearer that has kept it so popular at the jewelry stores.

Proportion is the single most important factor, because it determines the flow of light more than other quality factors. Proportions that are too deep or too shallow both allow light to leak out the bottom and lessen the amount of light reflecting back to your eye.

Good and bad cutting examples

Good and bad cutting examples
Proper cutting is what gives a gemstone its beauty and brilliance. Many people are confused about what a well cut gemstone looks like. There are no big mysteries about judging good cutting, it is very simple. When viewing a gemstone, looking at the table, a well cut gemstone will be very bright across the entire surface. This brightness is light being bounced around inside the gemstone, reflecting back to your eye.

You cannot see right through a well cut gemstone because almost all light is being reflected back towards your eyes. Poorly cut gemstones maybe too shallow or too deep causing what is called a "window". Windows are some thing that you are meant to look through and these are better left as windshields in you car or as windows in your home.
If you can see through a gemstone looking from the table down towards the culet, the point on the bottom, it has a window. If you can see through a gemstone it means that light is passing through it, along with colour and brilliance. Windows weaken the intensity of colour and severely affect brilliance.

Gemstones with windows are not desirable, they lack beauty and brilliance. You want gemstones that have "mirrors" that reflect back to you all of the beauty and brilliance that is yours to enjoy. As a general guide:
if the stone appears lively and exhibits an appealing colour when viewed through the table, no matter how the proportion appears (thick or thin), it is usually correct and acceptable proportioning for that particular stone.

Hardness, Refractive Index and Density

All gemstones have their own hardness, refractive properties and density. Gems that are harder have better wearing qualitites.

To measure hardness, the jewelry industry uses the Mohs Scale. This gem-trade standard, conceived by Friedrich Mohs in the early 1800s, measures the ability of a gem or mineral to resist abrasion damage. Diamond is placed as the hardest substance at 10, while talc is considered the softest at 1. Rubies and sapphires rate at 9, topaz and spinel at 8 and quartz material (such as amethyst and citrine) at 7.

Most of the objects you and your jewelry come in contact with are either quartz-based or near quartz's hardness. If your gems are harder than Mohs 7, they will not be scratched; if they are softer, they could get damaged. And, believe it or not, the precious metals your gems are set in (platinum, gold and silver) fall below Mohs 4.5.

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