WHAT IS GEMOLOGY?

Gemology is the science of identifying gemstones. This refers to the study of the fiscal, chemical and optical properties of the different mineral species that are currently traded in the jewelry industry and by others like collectors and investors. Once the physical, chemical and optical properties of the different mineral species are understood, gemologists utilize different types of equipment and techniques to test these properties for accurate discrimination and classification of the gemstone. A careful analysis by a professional gemologist will be able to determine the species of gem or mineral, if it is natural or treated and differentiate it from other simulants and synthetic counterparts. Deep gemological analysis by a reputable gem laboratory can give us deeper insight into the gem’s origin, quality and type of treatment if applied.

Gemologists evaluate many different factors and characteristics of each specimen to accurately discriminate and classify them. The most important factors are listed and explained concisely below.

• Chemical composition
  Kinds and relative quantities of atoms that make up a material. Quartz's chemical formula is SiO2, which means one atom of silicon and two of oxygen.

• Crystal structure
  Regular, repeating internal arrangement of atoms in a material. Crystals are categorized into 7 crystal systems depending on their different crystal structure. Each crystal system has its own characteristic crystal habit. The crystal habit is the shape in which every crystal system grows. Often, just by looking at the crystal’s shape and growth patterns a trained gemologist can identify the corresponding specimen.

• Hardness
  How well a gemstone resists scratches and abrasion. Different crystals have different degrees of hardness. These are classified using the Moss scale, which separates each crystal on a scale from 1 to 10 depending on their hardness. Diamond being 10 and talc 1. The harder the gemstone, the more durable. Harder stones can also take a better polish/luster and higher durability.

• Luster
  The appearance of a material's surface in reflected light. A gem with top luster would be a well-polished diamond. A gem with almost no luster would be opaque like lapis lazuli.

• Stability
  How well a gemstone resists the effects of light, heat, and chemicals. Some gems like Kunzite will fade in color when exposed to sunlight for prolonged periods of time. Other gem materials like Diamonds or Corondum will change color when heated.

• Toughness
  How well a gemstone resists breaking, chipping, and cracking. Calcite for example has cleavage plains which make it very easy to break if dropped or struck at the right angle. Jade, as opposed to kunzite, is one of the toughest materials in the mineral world. it is very hard to break or shatter even if struck with power.

• Transparency
  The degree to which a material allows light to pass through it. There are different degrees of transparency. The classification goes from transparent to semi-transparent, translucent, semi-translucent and opaque. High-quality jadeite is very translucent.

• Hue
  The first impression of an object's basic color.

• Fluorescence
  Emission of visible light by a material when it's stimulated by ultraviolet radiation. For some gemstones like ruby, fluorescence is a desired trait. The fluorescence produces a glowing silky appearance in daylight. In other gems like diamonds, fluorescence is considered a negative trait. Even though fluorescence does not cause the diamond to look bad in natural daylight it does give it a certain haziness when exposed to bright sunlight.

• Pleochroism
  When a gem shows different body colors when viewed from different directions. This is the case with gems like Tanzanite and Tourmaline. Here the cutter has to find the optimum orientation for the gem’s table to express the most desired color for the gem.

• Refractive index
  Degree in which the light slows down and changes direction while passing through a gemstone. RI is the ratio of the speed of light in air to its speed in the gem. The higher the density, the higher the refractive index. Most gemstones have a different and characteristic refractive index. This makes this factor one of the most useful and accurate when separating gemstones.

• Inclusion
  A characteristic enclosed within a gemstone or reaching its surface from the interior. Different gemstone species have different types of inclusions. Even within the same species of a gem, there can be differences in the type of inclusion which can be very useful to the gemologist when trying to identify natural versus synthetic and geographical origin of the gem. Inclusions can be small cracks or internal fissures, small crystals of other mineral species, liquid/gas inclusions and many more.

• Specific gravity (SG)
  The ratio of the weight of a material to the weight of an equal volume of water. SG gives us a density ratio that varies between gemstone species and can help us with identifying specimens. It is especially useful when evaluating rough material in the field and other tests that are difficult to apply.

• Origin
  Many species of gemstones, like emerald, ruby and tourmaline, vary in chemical composition according to their geographical origin. Trace elements like iron in ruby, vanadium in emerald and copper in tourmaline are present in different degrees and can help us with classification and origin determination.

• Single refractive versus double refractive
  Singly refractive gems possess the same physical or optical properties in all crystal directions. This means that it doesn't matter from which angle the light enters the gem; it will always continue in the same direction. Also, when you look at the stone, it will always look the same color. In double refractive gems, when the light enters, it will be divided into two rays with different directions with different refractive indices. This will also cause color variation when looked at from different angles (pleochroism).

• Absorption spectrum
  A pattern of dark vertical lines or bands shown by certain colored gems when viewed through a spectroscope. A spectroscope is a small device that separates the light that enters it into its different corresponding wavelengths of different colors. Each gem absorbs and transmits different portions of the white light spectrum so different gems transmit a different and unique absorption spectrum which can be utilized to identify gems.

• Direct observation under magnification
  Direct observation under a 10x loupe is the most powerful and useful instrument for a gemologist. Especially when you have to discriminate natural from synthetic stones. Natural and Synthetic stones are chemically identical so most of the tests will show no difference. Here comes into play, the skill and ability of the gemologist to be able to observe and discriminate directly the differences between a natural gem and its synthetic counterparts.