Gemologist explains on what sapphires are used for and how to spot a fake
Kazan Federal University has established a full technological chain for working with sapphires, from crystal synthesis and color modification to expert identification and specialist training.
Together with gemologist Anatoly Nikolaev, associate professor at the Department of Mineralogy and Lithology, we take a closer look at the differences between natural corundum – of which sapphire is a variety – and synthetic material, which is widely used not only on Earth but also in space.
“Artificial colorless sapphire grown under laboratory conditions is identical to natural sapphire in its chemical composition and basic physical properties, including hardness, density and refractive index,” the scientist explains. “They can be distinguished by their internal structure: natural stones almost always contain characteristic inclusions – tiny crystals, ‘silk’ formed by rutile needles, and growth zones that record how the crystal developed over hundreds or thousands of years in the Earth’s crust. Synthetic sapphires, by contrast, are often impeccably clean or display features specific to the growth method, such as curved growth lines or gas bubbles.”
Counterfeits are common in the gemstone market, especially when it comes to valuable stones such as sapphires.
“At home, one may identify a crude imitation, such as glass, by air bubbles inside the stone or by the fact that it warms up more slowly in the hand. However, only a specialist using dedicated equipment can make an accurate identification,” Nikolaev stresses.
To distinguish a natural stone from a synthetic one, KFU’s gemology lab uses a range of methods: optical microscopy, including immersion microscopy, to examine internal inclusions and growth zoning; optical absorption spectroscopy to analyze crystal-chemical features; and EDXRF and LA-ICP-MS spectrometry to determine the concentrations and types of trace elements.
“For a jeweler, the benchmark is a Kashmir sapphire with a rich cornflower-blue color. Its legendary velvety hue and exceptional rarity make such stones highly prized by collectors. For a scientist, however, the value of sapphire is determined not by its color but by the purity and structural perfection of the crystal. Perfectly clean, large synthetic sapphires are of greatest interest for optics, laser technology and microelectronics,” the gemologist says.
Like natural gemstones, artificially grown sapphires possess a unique combination of properties: high transparency across a broad wavelength range, chemical inertness, resistance to high temperatures – up to 1,900°C – and radiation, as well as exceptional hardness second only to diamond.
“Synthetic corundum is not merely an analogue of a gemstone; it is a strategic material for high-tech industries,” the researcher notes. “Its demand is explained by a rare combination of physical properties seldom found together in a single material. In optics and laser technology, sapphire is used as a substrate for lenses, prisms, light guides and components of solid-state lasers producing blue, green and white light, including microlasers. The crystal performs reliably under high loads and does not degrade under radiation. In microelectronics, sapphire substrates make it possible to grow epitaxial layers of silicon and gallium nitride, or GaN. This is crucial for manufacturing radiation-resistant microchips for nuclear power applications and space technology. In optoelectronics, corundum substrates are used to produce high-brightness light-emitting diodes, mobile-phone screens and laptop displays. In addition, artificial sapphire plates are used in body armor, scratch-resistant watch crystals and surgical scalpels.”
KFU has carried out a series of experiments involving pale-colored sapphires, resulting in an intensified original blue color as well as the production of yellow coloration, Nikolaev informs.
“Enhancement involves heat treatment or irradiation that changes the stone’s color, affecting either its entire volume or its surface layer,” the associate professor adds. “Such changes are generally stable over time. Enhanced stones are used mainly for jewelry, but crystal-treatment methods may also be applied to modify the properties of technical sapphires – for example, to control their transmission spectrum.”