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What Attributes Make A Gemstone Desirable?
It's worthwhile to ask what qualities are desirable in a gemstone. There are six main characteristics which are classically regarded as being desirable in a gemstone. These are in order of importance:- But let's look into each of these six properties more closely.

Beauty - Optical Attraction
Firstly a gemstone should be optically attractive, it can achieve this in various ways. It could be a beautiful colour, or it could sparkle through reflecting, refracting, or dispersing light. Note that all the aspects of beauty relate to what happens to light when it hits the gemstone.
We could subdivide Beauty into:-

Colour
We believe that the most important single gem characteristic is colour.
Gems such as ruby, amethyst, sapphire and emerald have attractive colour as their main attraction, and are generally expected to be transparent, however it is not necessary for gemstone to be transparent. Coral, lapis lazuli, cornelian and opal can all be considered beautiful, but are usually opaque.
Colourless stones, naturally, are bound to be less attractive or beautiful, or are they? Although sapphire, spinel and quartz and other gemstones can occur in colourless varieties, they are usually quite uninteresting because they do not have the advantage of possessing the beauty of colour. Diamond likewise is often colourless, but perversely, it is considered by many to be the most desirable gemstone.
The main reason why diamond is suitable as a gemstone is its high refraction and dispersion - now we are getting technical!
Let's consider colours for a moment rather than coloured gemstones.
Some colours are known to be high-preference colours, others will have high attention value. Yellow appears to have the highest attention value. Perception tests have shown that people will see yellow objects more quickly than other colours, brown and green are lower attention colours.
Other colours are high preference colours, blue is probably the highest preference colour, with red, purple and green following.
Naturally whatever people regard as their favourite colour is likely to be high on their desirability list when it comes to gemstones. This last fact makes it even more odd that many people's top choice of gemstone is diamond!

Sparkle
Actually it's necessary to consider why some stones sparkle more than others:-

Let's take these four concepts in turn, although as you will see there is some interaction between them.

Reflection
All stones will reflect light from their surface. The amount of light reflected will depend on the surface reflectivity of the stone. Although the reflectivity is related to refractivity, factors such as the hardness of the stone affect its reflectivity, partly though the ability of hard stones to accept a high polish.
The reflectivity of a stone at its surface is often referred to as its lustre.
Transparent stones will also reflect light from their internal surfaces. How strongly they do so depend on their refractive index. The proportion of light reflected off an internal surface increases suddenly at a particular angle for any pair of materials. This angle is known as the angle of total internal reflection. This angle is very important when determining the optimum cutting angles of different gemstones. Ideally all the light entering the stone from any angle would escape via the top (front) of the stone. The higher the refractive index of the stone, the more light will be reflected internally from the back facets.

Refraction
All materials refract light (alter its angle). The amount by which light is refracted is an important feature of every gemstone. The measure of a material's refactivity is known as its refractive index or R.I.
Without going too deeply into physics, light travels at different speeds through different media. When light passes from one medium to another, its path is altered (bent) and it is said by by diffracted.

Dispersion
Dispersion is the difference between the amount of refraction of different colours of light. White light is actually composed of light of all different colours. A highly dispersive material will split light strongly into its component colours to give a "prism" effect showing a "rainbow" or spectrum.
Dispersion is often know as "fire".
Diamond owes most of its beauty to its high dispersion, whereas white sapphire, with low dispersion tends to look "dead" or glassy.

Facetting
The number of facets on a gemstone, and their careful placement will tend to give a stone more sparkle, and enhance its beauty and desirability.

Size
In general, the larger a gemstone, the more obvious its beauty, and therefore the greater its desirability. A microscopically small gemstone may be of interest to a gemmologist perhaps because of its rarity, but would be of little practical use in jewellery. Obviously it is also possible for a gemstone to be too large to be of practical use in jewellery, in which case it could be recut into a number of smaller stones.

Shape
To some, a heart shaped stone may be more desirable than a different shape, but this is usually a matter of personal preference.
Some stones naturally occur in certain typical shapes, or lend themselves to be cut in certain shapes. Emeralds for example lend themselves to being cut into oblong or octagonal shapes, so that an oblong shape with its corners cut to form an octagon is known as an emerald cut.

Durability
Regardless of how beautiful a stone may appear, for it to be suitable as a gemstone, it will need to be reasonably durable. Gemstones do vary considerably in their durability, some, such as diamond, are almost indestructible, others are considerably more delicate. Indeed, one paradox of gemstones is that something so small and delicate-looking can be so strong.
It is important to realise that durability is not the same as hardness. For example, try bouncing a glass bottle and a rubber ball on a concrete floor. Glass is harder than rubber, yet the glass bottle smashes, and the rubber ball bounces. The rubber ball is more durable.

Hardness
There are numerous different ways of considering hardness, but the main one for gems is their resistance to abrasion. Moh's hardness scale lists 10 well known minerals on a scale from 1 to 10. Each numbered mineral will scratch the mineral numbered below it.
Diamond is shown as 10 on Moh's scale, and is the hardest naturally occuring substance. Even though diamond is very tough, it can be shattered by a hard blow, especially at an unlucky angle.
Corundum, of which ruby and sapphire are composed, is the next on Moh's scale at 9. Rubies and sapphires are both hard and tough.
Topaz is listed at 8, so is very hard, but it is relatively easy to break topaz, especially along its cleavage planes. It is said to possess perfect cleavage, and expression which always stirs my imagination!
Quartz, which includes amethyst and citrine, is listed as 7, and is the softest translucent material which is recommended for general jewellery usage as a gemstone. This is because most dust contains tiny quartz crystals, and because its hardness is 7, will scratch softer materials.
Emerald has a hardness of about 7.5, chrysoberyl 8.5, garnet 7.25 to 7.5, zircon 7.5, all these are of sufficient hardness to be useful as facetted gems.
There are a few gemstones which are transparent, and therefore usually facetted, and because of their other desirable properties, are frequently used in jewellery, and can be worn with care. These include sphene 5 to 5.5, zoisite including tanzanite 6, demantoid garnet and some zircons at 6.5, and peridot at 6.5 to 7.
Gems which are opaque do not show surface scratches as badly as facetted transparent stones, and therefore do not need to be as hard. Most opaque stones are polished into cabochons, with smooth rounded surfaces, as opposed to flat facets. Such gemstones include amber 2 to 2.5, pearl 2.5 to 3.5, coral 3.5, opal 5.5 to 6, and turquoise at 6.
Transparent gems can also be cut as cabochons, although coloured gemstones make much better cabochons than do colourless stones.

Rarity
Many authors and jewellers state that rarity is necessary or desirable for a gemstone. We believe that a beautiful and attractive gemstone is just as beautiful and just as attractive whether it is common or rare. Supply and demand usually dictate that rare objects command high prices. In our opinion, amethysts are often underrated despite their beautiful colour, because they are relatively inexpensive.
Only the status value of gems is increased by their rarity, not their aesthetic value, although there are mineral collectors who appreciate the value of possessing rare and unusual specimens whether beautiful or not.
Not all common gemstones are cheap, and some rare gemstones are probably undervalued. Diamonds, for example must be about a million times more common than alexandrite.

Natural, Synthetic or Simulant?
Again, many jewellers and jewellery consumers, insist that being natural is a necessary attribute for a gemstone. We do not completely agree with this. Certainly, we understand that ownership of a rare, expensive natural gemstone gives it owner a degree of status and personal satisfaction, but we don not believe that this makes a beautiful and attractive synthetic or simulated gem any less beautiful.
Our view may be a minority view amongst members of the jewellery trade, but we believe that the prime purpose of jewellery is, or should be, adornment.
We believe that the elitist stance of many jewellery professional is because they perceive synthetics as a threat to their profits and livelihoods. It is difficult to sell an expensive diamond to a customer who realises that synthetic gem quality diamonds can be manufactured, so it is only natural for many jewellers to resist the threat posed by progress.
We look forward to the day when we can offer a gem quality synthetically produced 1 carat diamond for 100! We believe there will still be a demand for the natural product also.
There is a difference between natural, synthetic, and simulated. Not all synthetics are simulants, and not all simulants are synthetic. A gem simulant is a a stone which appears similar or identical to another, different stone, so that cubic zirconia and natural colourless sapphire can both be used to imitate or simulate diamond. A synthetically produced diamond is a real diamond, not a simulant for diamond. Synthetic sapphire can be used to simulate alexandrite (not very convincingly), but can never simulate sapphire because it is sapphire.
Gemstone simulants have been made for about 7000 years. The ancient Egyptians used to make a turquoise coloured ceramic called faience in imitation of turquoise.
Synthetic gemstones are relatively recent. Synthetic ruby has been produced since before 1905, spinel from 1908, sapphire from 1911, and diamond from about 1950.
Cultured pearls are a simulant produced by a natural process induced by human interference. A cultured pearl is one which has been produced by an oyster, or other bi-valve, by inserting a bead, usually mother-of-pearl, into the oyster. The oyster then proceeds to coat the bead with nacre, from which natural pearls are also formed.

Fashion
Fashion can play a part in determining whether a material is regarded as a gemstone. Moonrock is quite rare and although quite unattractive, yet it would be considered a fashionable and desirable gemstone, especially if some famous person were to be photographed wearing it, and little else, to the premier of a high budget Hollywood film at the Cannes Film Festival.
Ivory is currently out of fashion as a gemstone.
Yellow and brown tinted diamonds are considered to be inferior to colourless ones, and so, in most ignorant folk's opinion would intensely coloured natural fancy canary coloured ones.
We believe that coloured diamonds may become the next jewellery fashion trend. We have always liked liked them, but they are not well appreciated in our corner of England. We also belive that De Beers will never dare to promote them because it might lead to people realising the beauty of coloured stones, whereas most diamonds are almost colourless.

Special Properties
By special properties, we include the possible health or social effects which gemstones can possess, so we include the following categories of superstition, religion, social custom, and health.

Health
It has long been believed that wearing certain minerals and gemstones can create beneficial health effects, amethysts for example were regarded as protecting the wearer from becoming drunk. Currently, we notice that there are many claims that unfacetted crystals can produce vibrations which protect the wearer from radiation or other hazards. We remain somewhat cynical but tolerant, and open-minded, about these claims.

Superstition
Superstition plays a part, we hear many people who belive that emeralds or opals are unlucky, or that "pearls are for tears". We believe that most stories such as this are ill-founded. Of course if an individual believes that a certain stone is unlucky for them, then there is little point us trying to convince them otherwise. Also if an individual believes a particular stone brings them luck, then we would not seek to upset their viewpoint. It this increases their self-esteem or confidence, then it may actually improve their quality of life. We strongly believe this to be a good thing, if gemstones and jewellery can create such a beneficial effect, perhaps it should be available on the National Health. (Of course, we don't know what would happen to waiting lists!)

Religion
Bishops wear large stone set rings as a symbol of their office, usually red or purple stones. Similarly red stones set in a cross or crucifix may have a special religious significance.
Different religions will also have similar practices.

Social Customs
In some societies and cultures, the wearing of gemstones, perhaps shells or beads, as jewellery may convey messages about the social status of the wearer.

Summary
The following chart could be used as a visual summary of the relationship between different desirability factors of gemstones.

You may wish to visit some of our other pages:-

A to Z of Gemstones - not quite complete yet!

Birthstones by Month

Hourstones

Zodiac Stones


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