World of Gemstones

Introduction

Do you know who received the world's first diamond engagement ring - and when? Or which gem Catherine the Great of Russia loved so much that she had an entire room made of it? Or which stone can be found in only one U.S. state?

Are you aware that diamonds were first worn for their powers rather than for their beauty? And that diamonds and sapphires come in almost every color? And that that there are gems more valuable than diamonds?

Have you heard of color-changing gems? Star gems? Cat's eye gems?

This handbook has been compiled to give you all this information - and much more. In it you will discover a fascinating world - the world of gemstones.

You've surely heard about the more famous gemstones like diamonds, sapphires and rubies, here you can learn about many, many more. Also, certain gemstone types of special interest (like green sapphires and pink diamonds) have been listed separately so they can get the special attention they deserve.

But no matter which stone we're talking about, each write up gives you some interesting and important facts. It might be the history of a gem or how it was discovered or the source of its name. You may learn fascinating facts about specific specimens of a stone or read about its relationship with famous, world monarchs. You may discover in what forms the stone can be found and also interesting physical properties it may display. You will gain necessary information like tips on caring for specific gems.

At the end of each write up, you will find a data chart with very specific information for each stone. The chart is divided into two parts. The first tells you about the gem's physical characteristics, like its color, hardness and where in the world it is located.

Here are terms you may want to understand before you look them up on individual gem charts:

Color - This simply tells you the various color hues of a gem.

Shape - Shape should not be confused with cut. Shape is simply the outline of the stone, what shape it has when you look at it face up. For example, it may have a round, oval, pear, triangle, rectangle or cushion shape. There are also fancier shapes like heart, marquise, baguette etc.

Cut - Cut is something much deeper than shape. It is the way in which the stone is faceted to make the stone appear as reflective and sparkling as possible. It refers to the way flat surfaces are cut into the stone.

Generally there is the cabochon cut and three basic faceted cuts. The cabochon is the oldest cut there is. The stone is polished to form a flat base and a smooth, round, domed surface. The three main faceted cuts are: brilliant, step or emerald, and mixed. In a brilliant cut, many, many facets are cut into the stone. In a step or emerald cut, the top of the stone is usually one large, flat and rectangular or square face and the edges are faceted. The mixed cut is a combination of the first two. This usually means that the top of the stone gets a brilliant cut, while the pavilion - the lower part of the stone - gets a step cut. And then there are also special or fancy cuts.

Hardness - Gem hardness is measured on Moh's scale. Viennese mineralogist, Friedrich Moh, developed a scale that classifies a mineral's hardness in comparison with other minerals. It ranges from 1 to 10, with 1 ranking softest (like talc) and 10 ranking hardest (like diamond).

Crystal System - Most gemstones are minerals, and most minerals grow in specific crystal forms. This means they display regular, geometric patterns of atoms, ions and molecules. This inner pattern affects the crystal's physical properties like its outer shape, hardness, cleavage, fracture, density and more. It is therefore helpful in identifying minerals.

These crystal forms are classified into seven different groups or systems: cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic and triclinic. There are also amorphous stones, stones with very weak or no crystal structure.

Refractive Index - When light hits the surface of a polished gem, some light is reflected but most of it is absorbed by the stone. And because the gem has a different density than the air, when the light rays reach the stone, they slow down and are bent - or refracted.

The refractive index measures the amount of refraction, how slanted the light rays become. Since the amount of refraction is the same in specific gemstone types, measuring the refractive index is one way of identifying a gem.

How do we get the refractive index number? Well, you can define refractive index as the relationship between the speed of light in air and the speed of light when it hits the stone. (When the light rays hit the stone, they move a little slower.) Divide these two numbers, and there you have it - the refractive index.

Birefringence - This technical-sounding word is related to refractive index. You see, when you look at a gem through a refractometer - the machine that measures refractive index - some gems show single refraction and some show double refraction. Single refraction means you can see one single shadow edge, while minerals that are doubly refractive show the light ray splitting into two so you can see two shadow edges.

You get the birefringence number by finding the difference between the refractive indexes of the two light rays. Gems that are singly refractive don't have birefringence. (They can't because since they show only one shadow edge, you cannot get two refractive index numbers for them.)

Pleochroism - A gem is pleochroic if it displays one color when you look at it from one direction and another color (sometimes even a few colors) when you look at it from a different direction. Minerals of the cubic crystal system and amorphous minerals show only one color, so they are not pleochroic. Tetragonal, hexagonal and trigonal show two colors (so you can say they are dichroic), and orthorhombic, monoclinic or triclinic can show three colors (which makes them known as trichroic).

Cleavage - Many gemstones can be easily split or cleaved along certain flat planes (because of their internal atomic structure). Depending on how easy it is to cleave a crystal, the stone will be considered to have perfect, good or imperfect cleavage. Some gems cannot be cleaved at all, so you would say they have no cleavage, only fracture.

Fracture - As opposed to cleavage, you get a stone's fracture by just breaking it anywhere. The broken edges that result can be described as conchoidal (where the edges look curved, rippling, shell-like), uneven, smooth, fibrous, splintery or grainy.

Density - You get a stone's density or specific gravity by dividing the weight of the gemstone by the weight of an equal amount of water.

Chemical Composition - This tells you what minerals the stone is made of.

Transparency - This tells you whether the stone appears transparent, translucent or opaque

Luster - Luster describes the kind of surface shine that a gem has, and this is determined by the way light is reflected from its surface. One thing luster depends on is how much it can be polished. The harder a stone is, the more it can be polished - and the more lustrous it can be.

Most gemstones have a glasslike or vitreous luster. Some, like diamonds, have an even more brilliant luster known as an adamantine luster. Gemstones can also have resinous, waxy, greasy, silky, pearly lusters. A stone that reflects very little light would be called earthy or dull.

Occurrence - This tells you where in the world the gem can be found.

The second part of the gemstone data chart tells you what month, zodiac sign, planet, anniversary year, chakra, day, hour and number the stone corresponds to.

If you're wondering what chakras are, according to ancient Eastern tradition, they are specific points (chakra is the Sanskrit word for wheel) of energy located throughout the body that correlate to certain nerve and endocrine centers. They are also associated with different colors and character traits.

It is believed that when the chakras are not aligned properly, the body develops all kinds of disorders like physical illness and mental stress. Gems of different colors are believed to have balancing, healing effects on corresponding chakras. For example, the fourth chakra is the heart chakra. It represents the heart, circulatory system, lungs, shoulder and upper back. Its parallel color is either green or pink, and it is said to help you love yourself and others. Therefore emeralds and green and pink tourmalines are some of the gemstones recommended for strengthening this chakra.