Sapphire Gemstone Information

Sapphire


Sapphire
is a precious gemstone that occurs as a transparent, blue variety of the mineral corundum. It is commonly accepted that anytime a corundum is red it is considered a ruby, and by any other color, a sapphire.

 

The true sapphire is deep blue. The term sapphire can be applied to other varieties of corundum: colorless is called white sapphire; yellow is called yellow or golden sapphire, or Oriental topaz; and pale pink stones are called pink sapphires. In retrospect, a gemstone commonly referred to as a “flaming pink topaz” could also be considered a sapphire; though this is not generally the case.

 

The Sapphire is a result of Aluminum Oxide and the colors are caused by small amounts of impurities in the aluminum oxide (Al2O3) of which the mineral is composed. Star sapphires display a multi-rayed star in the stone's interior. In 1969, the Star Linde Sapphire hit the Market which was the first known synthetic of the star sapphire. It can be related that since the Star Linde came into existence, most Star Sapphires in circulation are of the Star Linde Variety. The gems occur in various parts of Asia, Australia, and the United States.

 

On the Moh’s Scale of Hardness (scale of mineral hardness graded from 1-10) the sapphire is considered to be second in hardness to that of a Diamond (Moh’s Hardness Scale: 10) with a hardness of 9. Some relate that as a corundum, in our case the sapphire, can cut or scratch another sapphire, the corundum is therefore properly considered ½ degree harder than 9. This may have merit, but for the purpose of the Moh’s Hardness Scale, which is an accepted industry standard and has been for many years, it does not grade in ½ degree increments.

 

The hardness is commonly associated with the strong and short oxygen-aluminum bonds contained within the mineral; bonds which pull both the oxygen and aluminum close together at the sub-atomic levels making the crystal not only quite hard, but also quite dense for a mineral element made of two light elements (aluminum and oxygen). In scale of hardness, the Diamond at a hardness scale of 10 is 140 times harder than that of a corundum.

It is very similar to that of a
Tanzanite, Blue Spinel and Blue Tourmaline when faceted. In the natural state, it looks similar to Ruby. However the similar minerals noted herewith, except for the ruby, both differ in hardness and are too soft to be mistaken for a sapphire. Buyers should be aware of the less commonly known sapphire from Brazil that is made from clear quartz.

 

It can be used as an abrasive and emery is made from them. It is also being used as a refractory type of material in very high temperature kilns. It has also been used as a surface treatment on special tiles in the commercial retail arenas that guard against slippage on wet floors.

 

Sapphire crystals are commonly used in infra-red optical scanners, watch crystals (citizen is a common brand of watch that uses them), very high durability windows as well as other uses such as wafers in semi-conductors, the most common type being the GaN Nanorods used primarily in the nanotechnology fields. GaN is a very hard material that is most commonly used in bright led’s (light-emitting superconductor diodes that are commonly used as indicator lights on many electronic devices (such as TV’s, Radio’s, Calculators, and even Watches, among others).

 

Common corundum, which includes all dull, opaque varieties, is usually light blue to gray, brown, or black. It occurs in feldspar bearing igneous rocks as an accessory mineral, in re-crystallized limestone, in placer sands, and in aluminum-rich metamorphic types of rocks.

 

Famous sapphires include the 563 carat "Star of India' and the 330 carat "Star of Asia." Sapphires can come in a variety of colors and can be treated and enhanced in various ways. They are also primary stones when it comes to synthetic versions.

 

Sapphire is the birthstone for September and due to its overall hardness it can be used, and is an excellent choice for items used everyday.

 

According to the American Gem Trade Association (AGTA® - the recognized foremost authority in colored gemstones in the United States), Sapphires can have treatments such as irradiation, diffusion, and heat. Special care should be given to each form of enhancement to avoid problems. Some types are more stable than others.

 

Under normal care conditions, for stone that is not treated or enhanced, refer to our general care guide above.

 

Other Useful Properties of Sapphire

 

Mineral Name

Sapphire

Mineral Family

Corundum

Specific Gravity

3.9-4

Refractive Index

1.762-1.778

Moh’s Scale of Hardness

9

Composition of Minerals

Aluminum Oxide

Crystal System

Hexagonal

Optical Properties

Abbe (v) Number

72.2

 

Optical Properties and Refractive Index
Including the Abbe (v) number reference

For this definition, and for sake of reference, to provide the reader with a greater understanding, we will refer to the Sapphire, of the Corundum family of minerals.

 

1.    Named after Ernest Abbe (1840-1905) a German Physicist. In both physics and optics, the Abbe Number or more commonly known as the V-Number or even constringence of a transparent material is the overall measure of a materials dispersion in relation to the refractive index.

 

The refractive index, or as it is sometimes called, the index of refraction is a measure of how much the speed of light (or other such wavelengths, such as sound and otherwise), is reduced inside the actual medium that it pertains to; or in our case to that of a corundum.

 

It should be noted that common glass has a refractive index of 1.5 which means that in glass, light travels at 0.67 times the speed of light in a vacuum (1/1.5). We can also refer to it as N=C/Vp (c divisible by Vp) whereas N is the median (such as our corundum) 3is the wave and Vp would of course be the phase velocity 2 in the actual corundum itself. For sake of reference, we can also refer to Vp as Pv (the phase velocity (or the rate at which the actual wave is moving in a given median which in our case would be how fast light is traveling through the corundum measured as seen below under sub-note 3 below, in direct relationship to the speed of light)).

 

Although Phase Velocity (and Velocity Phase) is most commonly used in reference when speaking about light and its relationship with that of a vacuum, historically it can be seen that other reference mediums have been commonly used as well to measure certain relationship to matter; one example being that of air within a standardized pressure or temperature.

 

2.    It should be noted in our example given above, Phase Velocity is defined as the rate at which the upper crests (ridges) of the waveform propagates  Or in simpler terms, that rate at which the wave length is moving through the actual medium itself. Again, in or example, the medium being referred to is that of the corundum. (for our example, you may see the upper wave crest the same as would you say this W, whereas the top 3 horizontal tips of the W, would be the upper crest. Or a better example may be that of a tilde ~ which resembles a wave. The upper area of the tilde, where as it forms into the n-shape, would be the upper crest of the waveform).

 

3.    C in this case is commonly used in Speed of Light equations. In such case one should be aware that in physics, the speed of all electromagnetic radiation in a vacuum travels at the same rate at around 3x10 8 (eighth power) per second, and is therefore seen as our C.  Therefore, in our example, if Vp (or PV ) is the phase velocity (or velocity phase) of radiation of a specific frequency in that of a specific material, in our case the mineral corundum, then the overall refraction index can be seen as n=c/v (the speed of light divisible by the velocity). or adversely, v=c/n.  In terms of our example, we can now safely say that using the equation, v=c/n, that Velocity V is directly proportional to the optical waveform measured in relationship of how fast it is traveling in terms of the speed of light C, through the corundum n. Following standard protocol given the outlined variables in relationship to the speed of light, outlined under this example, one can safely use it to measure all type of index factors when it comes to refractive and optical properties of gemstones.