The Gemstone Guide

Buying Guide

Introduction

Gemstones are the jewellery designer’s way to add colour and allure to a jewellery creation. Historically, gemstones have been used for thousands of years since their colours, hardness, shine and rarity made them appealing to their owners. Oftentimes gemstones, across cultures, are attributed with special powers. This thought is found in the concept of Navratna, where each of the nine stones represents a planet. The Navaratnas are the sacred nine gemstones as per Vedic texts and Indian Astrology that have a profound impact on human life. These Navratnas are linked to the nine planets and are also referred to as the Navagrahasj. In the Western world each zodiac sign is linked with a “Birthstone”. Traditionally there are three Precious Gemstones, namely Emerald, Ruby and Sapphire. However there are hundreds of other gemstones, previously known as “semi-precious” that are now called "Fine Gemstones”; acknowledging the fact that some rare fine gemstones, such as aquamarine or tourmalines can command a much higher per carat price than an average precious stone. Tanishq offers a wide selection of precious and fine gemstones that are sourced by our expert gemologists for our unique jewellery design creations.

Gemstone Anatomy

A coloured gemstone is the naturally occurring crystalline form of a mineral. Depending on the gemstones’ crystalline structure, it can be transparent, translucent or opaque. To bring out the best of the gemstone’s colour, there are a multitude of different cut types:

Ranging from the best-known faceted cut type, to the buff-top cabochon to special mixed cuts, where to top of the stone is a cabochon and the bottom is faceted; there are many variations to these most prevalent cut types. There are also gemstone beads in many shapes and styles available, as well as flat cut gemstone slices, as well full three-dimensional objects.

The function of the cut is to display the gem’s inherent beauty to the greatest extent possible. Since this involves aesthetic preferences on which there is little consensus, such as shape and faceting styles, the cut is the most subjective of the quality attribute analysis

 

Cut

A good faceted cut enhances and reflects light evenly. The faceted cut is designed to create maximum brilliance and scintillation in the most symmetrically pleasing way. Faceted gems feature two parts, crown and pavilion. The crown’s job is to catch light and create scintillation, while the pavilion is responsible for both brilliance and scintillation. If a gem is cut too shallow, light will pass straight through the gem, rather than returning the light to the eye as brilliance. This is termed a “window”. In well-cut gems, most light returns as brilliance. Brilliant areas are those showing bright reflections. Extinction is used to describe dark areas where little or no light returns to the eye. The proportions of the cut are often dictated by the shape of the rough stone material. Many times gemstones are cut to optimize the yield rather than keeping the beauty of the individual stone in mind. There are no fixed rules for cutting coloured gemstones, and often the cutter makes a decision based on the location or size of an inclusions in the gemstone. The objective is to minimize undesirable effects and maximize colour and brilliance.

Clarity

In natural gemstones, clarity describes the amount of clarity characteristic that are present in a stone. These clarity characteristics are divided into two types, inclusions; which are found inside of the gemstone and blemishes, which are present on the outside. Flawless coloured gemstones are more rare than flawless diamonds. Nevertheless, even though clarity is important in coloured stones, it does have the same effect on value compared with colourless diamonds. A valuable emerald will feature many inclusions, because the natural process of emerald formation is fierce, resulting in abundant natural flaws in even the most valuable emeralds. Also, lighter coloured stones need to be cleaner, because their flaws can be detected more easily. Darker coloured stones can hide their defects, because of their depth of colour. The location, the type, the size and number of inclusions or blemishes are important when evaluating the clarity of coloured stones. Inclusions may also be used to identify the origin of a stone.

For the evaluation of clarity, coloured gemstone are divided into three classification categories; reflecting differences in the geological conditions under which they are formed and how those conditions affect the physical appearance of the gemstone. For the purpose of grading GIA distinguishes the following three clarity categories: Type I, Type II and Type III.

Type I – Gemstones form under geological conditions in which inclusions are not very noticeable and such gemstone are often "eye-clean."

Type II – Gemstones form under geological conditions that are more severe, resulting in the presence of inclusions that are typically more noticeable. Sapphires fall into the Type II gemstone category.

Type III – Gemstones form under the most violent geological conditions, resulting in gemstones that typically show inclusions, visible to the unaided eye, and are rarely "eye-clean."

Polish

Gemstones are polished to give a shiny finish to the facets, or to the surface area of cabochons, beads, and carved gemstone objects. The finer a gemstone surface is polished, the better it will allow light to refract through the stone and reflect off the surface. A gemstone’s polish is largely contributing to its sparkle.

Emeralds are among the most precious of natural gemstones, along with rubies, and sapphires. Emerald is a sub-type of the mineral family beryl. Trace elements of chromium and occasionally vanadium are responsible for the green colour. Depending on the concentration of these trace elements, emeralds can appear light green to a very deep, dark green. Of all green gemstones emeralds are the best known and most popular, followed by Jade which holds a special value in China and Korea. Very light shades of green beryl are simply called Green Beryl, if they bear a yellow or orange hue they are called Heliodor. Pink or salmon colour beryls are known as Morganites. The most rare type of beryl is the red variety called Bixbite; it is among the top ten more rare gem varieties in the world. Another famous representative of the beryl family is the aquamarine, where iron is the trace element that is responsible for providing the gemstone with its blue colour.

Color

Considered to be the most defining characteristic of a coloured gemstone, the colour is the most prominent value attribute. The colour of an emerald is the most important factor as far as pricing emeralds is concerned. The value attributes of the colour are broken down into three components: hue, saturation and tone. An ideal emerald will have a good balance of all three colour components. The most prized emeralds are very transparent, feature even colour distribution and display no eye visible colour zoning.

Clarity

Emeralds frequently feature numerous inclusions and surface breaking fissures. The clarity of emeralds is graded by eye, and not with 10 x magnification as common in the clarity grading of diamonds. Therefore, if an emerald has no visible inclusions or blemishes that are visible to the eye, it is graded as flawless. Emeralds without surface breaking fissures are immensely rare. If the feasures of an emerald are filled with colourless oil, the clarity of the emerald and connected to it, the transparency are improved. While treatments of colourless oil represent an industry standard, treatents with green oil are considered deceptive since the oiling is not only improving the clarity, but influences the colour as well. Emerald treatments with oil are considered enhancements and need to be disclosed to the customer. The most expensive emeralds are eye-clean stones of an intense primary green hue with no more than 15% of any secondary hue.

Colour

Blue sapphire is valued as a primary colour gemstone. The purity of the primary hue, determines the valuable of the gemstone. Trace elements of titanium and iron give blue sapphires their colour; with increasing concentration of titanium and iron the colour saturation is improved. Violet, green and purple are the most common secondary hues in blue sapphires. Violet and purple hues can add to the overall beauty of the colour. Green however is considered to be the dismay of a blue sapphire. While almost all blue sapphires have a greenish component when viewed at a certain angle, it is the talent of the gemstone cutter that ensures that the green is not part of the face up position in a sapphire. Sometimes gray is included in the overall colour of blue sapphires, giving the sapphire a cold and steely appearance, compared to the regular warm hue of a sapphire.

Clarity

Eye-clean blue sapphires are rare, particularly in larger sizes. Therefore, blue sapphires with a small amount of internal inclusions are still very valuable, provided the inclusions do not diminish the brilliance, blurr the colour, or impact the gemstone’s transparency. Blue sapphires in carat weights larger than 1ct are normally not cut to calibrated sizes or into standard shapes, but each gemstone is evaluated and cut such that the colour and final carat weight is optimized. When cutting blue sapphires, the cut can affect the colour in amazing ways. Sapphires have a dichroic nature, which menas that their colour appears different depending on the angle from which the sapphire is seen. In one direction many blue sapphires appear blue to violet-blue, whereas inspected from another direction the appearance is somewhat greenish blue-ish. If the gemstone cutter is selecting the orientation of the stone such that the violet-blue colour is seen through the sapphires crown, the gemstone will look more appealing and is more valuable.

Star Effect

Some rare and prized blue sapphires display a star effect. The phenomenon is called Asterism and describes gemstones exhibiting a luminous star-like shape when cut in cabochon shape. A typical asteria is the star-sapphire, mostly a bluish-grey corundum, milky and opalescent, displaying a star of six rays. This effect s caused by so called silk inclusions. The inclusions must be long, and are thin and needle-like. The star effect is caused when the light is concentrate into 3 rays that intersect at right angles to the direction of the needles. therefore we get a six-rayed star. Small needles of rutile are oriented inside the minerals in the direction of the crystal growth system. There is relationship between the gem's growth and the number of rays produced by the reflected light. Not all silk inclusions cause a star effect though, but they are considered acceptable, as long as they are not so abundant that they adversely affect the brilliance or colour. May gemstones connoisseurs appreciate the presence of intact rutile silk, as it is an indicator for an untreated sapphire. Most sapphires are heat treated to increase the depths of colour and transparency. In the process of heating the gemstone the rutile silk is removed. The most important characteristic of sapphires is its excellent hardness. Moh's scale shows the hardness grade 9. The hardness of sapphire placed with ruby just after the diamond. Sapphires are easy to care and handle because of their great durability. Heat treatment is an industry wide accepted treatment for blue sapphires and approximately 90% of the sapphires in the market are thought to be heat treated. Naturallu an untreated blue sapphire is much more rare and valuable than a treated one.

Yellow sapphires are the most sought after colour gemstone, right after blue sapphires. Because of their brilliance rivals that of fancy yellow diamonds, yellow sapphires are very popular as engagement ring gemstones. The colour of yellow sapphires can range from an intense yellow, to yellow-greenish hues right to faint yellow hues. While the bright yellow varieties rule the engagement ring market, there is also a demand, mostly from Asian countries, for deep orange-yellow colours that are increasingly popular there.

The colour of yellow sapphires is cause by the trace element iron. The higher the concentration of the trace elements, the more intense is the colour saturation. However, some yellow sapphires also feature the trace element titanium, which lends the yellow colour an undesirable greenish tint. Therefore titanium-free yellow sapphires are higher valued than those containing titanium traces. Some yellow sapphires are coloured by natural irradiation, but nowadays lab-created low-level irradition is used to improve the appearance of colour in yellow sapphires. Artificially irradiated sapphires are known to fade over time, particularly when exposed to light and heat. Fully untreated yellow sapphires with a deep colour saturation are very rare. Yellow sapphires are less included than pink and blue sapphires, the high clarity attrbute combined with a deep colour saturation are the driving value factors for yellow sapphires. Due to the fact that yellow sapphire rough is less costly than blue or pink rough, gemstone cutters have given the optimization of brilliance a higher priority. The thought of conserving as much weight of the original rough as possible is of lesser importance resulting in a good availability of well-cut yellow sapphires in the market. Yellow sapphires are also oftentimes cut in fancy shapes, such as the radiant cut, as this cut is enhancing the colour of the gemstone

Rubies, just like sapphires are part of the corundum family. It is the presence of the trace element chromium that gives a ruby its colour. Red varieties of the corundum class are called ruby, whereas pink varieties (also coloured by the trace element chromium) are known as pink sapphires. Genrally spaking, it is the saturation of the colour that creates the divising line between what is called a ruby and what is considered a pink sapphire.

Colour

Colour is the primary attribute to consider when evaluating a ruby, followed by the clarity, or the degree of transparency. Objective colour graduation has been challenging to accomplish for rubies. Outdated trade terms such as “pigeon’s blood,” “saffron,” and “China Rose” have been utilized to define the colour of a ruby. These terms are not interantionnaly accepted and carry a high degree of subjective evaluation. Only recently an objective system for evaluating rubies was developed and implemented.

The colour boundaries of pink and red are often vague. When evaluating red rubies, the most desirable colour is a vivid, medium-dark red to a slightly purplish red and a strong saturation. Rubies from Myanmar have a faint purple secondary colour, whereas Thai rubies display a garnet red colour, which is caused by their dark tone. Rubies which feature fluorescence can benefit from the attribute by a more intense and deeper colour. Rubies with rutile needle inclusions benefit from the reflection of light .

Clarity

Like sapphires, rubies are not examined under 10 power magnification when determining the clarity. If no inclusions or blemishes can be detected when viewing the gemstone with the unaided eye, they are considered “eye-clean”.

Rubies are found in many places around the world, namely Sri Lanka (Ceylon). Vietnam, Thailand, Afghanistan, Africa, Cambodia, India, Kashmir, Laos, Nepal, Pakistan, Tajikistan and the United States. However Myanmar, formerly known as Burma, has been the primary source of the highest quality rubies for centuries. The famous Burmese ruby features the ideal combination of colour intensity, silk, and strong fluorescence.