Corundum Crystals and Chemical Elements

What is a sapphire?

Sapphires and their close relatives, rubies, belong to the corundum mineral. In gemology,“Kind”It is a mineral with a clear chemical formula and a specific three-dimensional structure.

How are sapphires classified?

Corundum (a mineral) comes in many different varieties. Many of these varieties are not as rare or precious as sapphires.“Emery”It is a common corundum used as a commercial abrasive.

Different varieties of corundum differ in color, transparency, internal characteristics and optical phenomena. As a type of corundum, sapphire is available in a variety of colors, except red. In essence, rubies are red sapphires because they belong to the same type of corundum, just different varieties.

Chemical composition of sapphire

Sapphires and rubies are corundum, which is an aluminum oxide (Al2O3). Corundum has a regular crystal structure formed by repeating an arrangement pattern at the atomic level. Crystalline minerals are divided into seven different crystal systems, separated according to the symmetry of their repeating atomic units.

Corundum has a trigonal crystal structure and consists only of aluminum and oxygen. It needs a silicon-free environment to grow. Since silicon is a very common element in the earth's crust, natural corundum is relatively rare. In the purestEnvironmentIn, corundum is colorless and transparent, forming white sapphire. Only with the addition of trace elements can corundum acquire rainbow-like colors.

The blue color of blue sapphire comes from the mineral titanium in the crystal. The higher the concentration of titanium in sapphire, the higher the color saturation. Too much color saturation will create a dull or too dark effect in the blue sapphire, which is undesirable and reduces the price of the stone. Blue sapphire also requires trace amounts of iron.

Iron as a trace element in corundum produces green and yellow sapphires, and when mixed with titanium, blue sapphires are produced.

There are two distinct reasons why sapphires appear yellow. The most common cause is trace element iron. In general, an increase in iron concentration increases color saturation. Trace elements of titanium can cause undesirable green castings in yellow sapphires, and the most valuable stones are relatively titanium-free.

Yellow sapphires can also be colored naturally by low-level radiation from the Earth's interior or by laboratory-induced radiation. Lab-grown sapphires are harmless to humans and not radioactive, but their color is known to fade with heat and light. For this reason, most consumers avoid them.

In addition to irradiation, yellow sapphires are often subjected to intense heating and diffusion treatments. Heat treatment converts worthless blanks into marketable gemstones, greatly increasing the supply of attractive yellow sapphires on the market today. Unheated yellow sapphires with high saturation are still very rare.

Chromium

Most pink sapphires have traces of chromium. Very high chromium concentrations produce rubies, while lower concentrations produce pink sapphires. If the trace element titanium is also included in the crystal structure, the sapphire will have a more purplish-pink hue.PadparadschaAnd orange sapphires need to contain both iron and chromium.

The color of purple sapphire comes from the presence of trace amounts of vanadium minerals. The element is named after vanadium, an ancient Nordic name for the Scandinavian goddess Freya. Vanadium occurs naturally in about65In mineral and fossil fuel deposits, it is the first content in the earth's crust.20Rich elements. The purple color in sapphire is formed by a small amount of vanadium; a larger amount will result in a color change of sapphire.

In addition to its many beautiful colors, corundum has some very interesting properties.