Gemstone Guide

A gemstone is a mineral or fossilized organic material that can be cut and polished for jewelry. To qualify as a gemstone, it must have rarity, beauty, and durability. Color, cut, clarity and carat weight are important criteria for gemstones, precious and semiprecious. Well-known examples are diamonds, rubies, sapphires and emeralds. Several organic materials like coral or pearls are also considered gemstones.

Gemstones, found in their rough state within the earth, are cut to enhance the naturally existing properties of the mineral or crystal. Many gemstones have natural inclusions or flaws. When examining gemstones, artisans determine the optimal cut to reflect the most light and enhance the tone and hue of the gemstone's color. Common shapes are round brilliant, marquise, oval, pear, heart, emerald and princess cuts. Cabochon (domed and without facets), and fancy cut (specially shaped) are unique options offered to consumers.

Gemstones can be found all over world. Minerals form beneath the earth's surface over millions of years under extreme pressure and/or heat. Only under certain circumstances will a mineral crystallize to form a quality fine enough to be deemed a gemstone.



Color is the most important factor in determining the beauty and value of a gemstone. There are four main factors involved in a gemstone's color: hue, saturation, tone, and distribution.


Hue is the term used for the actual color of the spectrum: red, orange, yellow, green, blue, indigo or violet. The more pure a gemstone's hue, the more valuable it is. Because gemstones are composed of many naturally occurring elements, they typically emit one dominant color and one or more underlying colors.


Tone represents how light or dark a stone appears depending on how much brown, black, gray or white is present.


Saturation is the intensity of brightness of the color. The more color saturated a gemstone is, the more valuable it becomes.


Distribution is how evenly the color spreads out across the body of the gemstone.


The cut of a gemstone is another important criteria for evaluating its beauty and worth. A good cut should be proportioned to display a gem's depth of color and liveliness while revealing the fewest imperfections. Colored gems are either cut with facets, many angled sides as found with diamonds, or cut as a cabochon, a smooth dome without facets.


Clarity is defined as the absence of inclusions (internal flaws) or external imperfections. Almost all gemstones contain some degree of blemishes. Flawlessness in colored gemstones is very uncommon and valuable.


A gemstone's weight is measured in carats, as with diamonds. As a rule, as a gem increases in weight, it will increase in value per carat. For gemstones, carat weight is not always an accurate measure to determine size. Most gemstones have varying densities (mass) that result in varying weight per carat. This means, for example, that a diamond and emerald of the same size will not have the same carat weight.


Almost all gemstones have been enhanced by various treatments to improve their appearance. Enhancements or treatments are an accepted part of the polishing and finishing process in the jewelry and gemstone industry. Standard accepted methods of enhancement are oiling and heating. Oiling is a process of soaking a stone in mineral oil, most commonly practiced on Emeralds. Tiny fissures or cracks on the gem's surface may appear whitish. When these imperfections are filled with oil, they become almost invisible. Heating is a permanent treatment where gemstones are subjected to high temperatures in order to enhance the color or clarity. In this practice, extreme temperatures further evolve the natural gemstone creation by lightening, darkening or even completely changing its hue and dissolving some tiny inclusions. Rubies have been heated to achieve the ideal rich "pigeon blood " red color since this gemstone was discovered many centuries ago. Natural sapphires, emeralds and rubies that have never been enhanced or treated are very rare and extremely expensive.


Hardness is a stone's ability to resist scratching, surface inclusions, abrasions or cracking. Austrian mineralogist, Friedrich Moh, devised the Moh's scale in 1812 to measure a mineral's hardness and its resistance to scratching. The scale goes from talc as number 1, being the softest, to diamonds as number 10, being the hardest substance known.



There are many different types of colored gemstones, some of which require specific care and cleaning procedures. However, there are some general care and cleaning rules that apply to all colored gemstone jewelry.

Many natural gemstones are treated or enhanced after they are extracted from the earth by one or more traditionally accepted jewelry industry practices. These treatments and enhancements can affect how you should clean and care for your colored gemstone jewelry.

After wearing, wipe your precious gemstone jewelry thoroughly with a clean, soft, slightly damp cloth. This will enhance the gemstone's luster and ensure that your jewelry is clean before storage. Store gemstone pieces individually in soft pouches.

Do not expose your precious gemstone pieces to salt water or harsh chemicals, such as chlorine or detergents. These chemicals may slowly erode the finish and polish of gemstones.

Hair spray, perfume and perspiration may cause jewelry to become dull. Apply all cosmetics, perfumes and colognes before putting on colored gemstone jewelry. Make sure to wipe your gemstones after wear to remove any chemicals, oils or perspiration.

Do not subject gemstone jewelry to sudden temperature changes.

If you have an active lifestyle, take extra precautions with some types of gemstone jewelry. Emeralds, for example, are brittle and should not be worn when doing household chores or any other activity where the stone could be hit or damaged.

Be extra careful with ultrasonic cleaners. Some gemstones are fragile and can be damaged by ultrasonic cleaners.

Gemstone care information provided in cooperation with Jewelers of America.