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Gemstones

Gemstone types

What distinguishes an emerald from a ruby?

Gemstones can be found in many different types and are very common in the jewelry industry. There are five essential features describing the quality of a gemstone: color, carat, hardness, clarity and cut. Of those, hardness is the primary factor in the evaluation of gemstones

Color

The color of a gemstone is its most characteristic feature and is considered by gemologists to be the most important in estimating the gemstone’s value. For evaluation, color deviance, tone depth and saturation are studied first. It is worth mentioning that if all lengths of a light wave pass through and/or are reflected, the object is colorless. If all the lengths of a light wave are absorbed instead, the object is black.

Color deviance

The most valuable gemstones can change their primary color slightly. For example, sapphires which can be rose to purple-rose or rubies with a color range from orange-red to purple-red are often more valuable.

Depth

The tone of a gemstone describes the color depth. The scale is from colorless to black. The scale which is most often used describes the color as light, medium light, medium, medium dark and dark. The most desired gemstones are usually between medium light and medium dark.

Saturation

A saturated gemstone is free from brown and gray shades. The fewer shades a gemstone has, the more it is worth.

Carat

The carat of a gemstone is not necessarily a measure of its value. Different types of gemstones have different densities which means that two stones with the same size can have different weights. For example, a one carat ruby is smaller than a one carat diamond.

Hardness

A stone’s hardness is determined in Mohs. Mohs provides reference to practical usage, when a stone is supposed to be worn. Number 1 is the softest and number 10 is the hardest grade. This table describes hardness in Mohs for common gemstones.

Gemstone

Hardness (Mohs)

Turquoise

5-6

Opal

5½-6½

Moonstone

6-6½

Jade

6½-7

Peridot

6½-7

Amethyst

Citrine

Tourmaline

7-7½

Aquamarine

7½-8

Emerald

7½-8

Topaz

Ruby

Sapphire

Diamond

Clarity

Almost all gemstones have inclusions. Gemstones which are completely clear are very unusual and valuable. There are, however, many gemstones with only some trace of other minerals which makes them more valuable. Therefore there is no simple way of estimating the value of a gemstone based on its clarity.

Cut

Unlike diamonds, there is no scale or range to grade a gemstone’s cut. Instead, the grading includes how well the cut was done in relation to the stone’s color and inclusions. A good cut shows good symmetry and proportion in relation to color and inclusions. Unusual gemstones are sometimes cut to make the size bigger rather than to maximize the gemstone’s brilliance.

Treat

Almost all gemstones have been treated and improved. Gemstones which have not been improved but still have fine quality are extremely rare and valuable. Unpolished gemstones usually do not look so impressive. Almost all gemstones in the jewelry industry have been treated by temperature. Temperature completes and finishes what nature began. The jewelry industry accepts this kind of treatment as a natural part of the gemstone’s improvement process.

Tips on how to care for your gemstones

To clean a piece of jewelry with gemstones, use a solution of water and mild washing liquid. Let the jewelry lay in the water bath for about 20 minutes, scrub it afterwards carefully with a soft (really soft) toothbrush. Ultrasound bath is not usually recommended for cleaning gemstones. Rubies and sapphires can survive the ultrasound bath but other gemstones are too sensitive. Opals and emerald can never be cleaned with ultrasound.

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