Corundum stone: types and properties. Video
In the world of minerals, corundum is known for its variety of colors. Due to its beauty and extraordinary hardness, this stone has long won popularity among people. Today, two of its varieties are at the top of the list of gemstones, along with diamond and emerald.
Corundum stone: types and properties
Corundums: technical and jewelry
Many stones, similar in properties, but different in appearance and application, are united by one name – corundum. In its pure form, it is almost never found in nature, but its compounds with other elements are widespread. Abrasive substances are made from ordinary corundum, which is unsightly in appearance. However, a small number of corundums have a clarity, clarity and color that qualifies them as gemstones.
Jewelry corundum has a wide range of colors. Pure corundum consists of aluminum oxide and is colorless. Reacting with a small amount of dye metals (chromium, iron, titanium, vanadium, cobalt, nickel), it acquires a variety of colorful colors: red, blue, pink, cyan, green, yellow, violet, purple, orange, brown, white , GREY-black.
Corundums of red shades are called rubies by jewelers, and stones of all other colors are called sapphires. These names have been entrenched since ancient times, when it was not possible to recognize the kinship of the stones. Sapphires and rubies are among the most valuable and expensive gemstones.
Ruby means red, and this color gives corundum its chrome. For a ruby, color and transparency are of great importance. As a natural stone, it may have minor imperfections, however, rubies that do not have dark or light spots are more appreciated. High quality stones should have a distinct color in any light. The most expensive rubies have a rich, uniform color from red to purple (the color of “pigeon blood”). Large rubies are less common than large diamonds. Rubies are often heat treated to improve color and clarity. The main producers of rubies are Myanmar, Thailand, Cambodia, Vietnam, Sri Lanka, Kenya, Tanzania and Madagascar.
In addition to being used in jewelry, rubies are also used in laser technologies, lenses, high-quality watch movements.
“Sapphire” means “blue stone”, and it is with this color that sapphire is associated with many people. The blue color of corundum is given by iron and titanium. The most valuable sapphires are blue and cornflower blue stones. If the word “sapphire” is used independently, it refers specifically to the blue stone. To designate sapphires of other colors, qualifications are used: green sapphire, yellow sapphire. In addition to color, a quality stone should have a uniform color.
There are special names for other types of sapphire:
- leucosapphires
- fancy sapphires
- subordinate
Leucosapphires are colorless transparent stones, also called white sapphires. They are created by heat-treating dull sapphires. Currently, leucosapphires are used as cheaper substitutes for diamonds.
Fantasy sapphires are colored stones in all shades except blue. The most valuable are the more transparent sapphires of bright colors. For pastel colored stones, it is especially important that they have as few visible inclusions as possible. Cutting is also very important for light tones: thanks to the uniform reflection of light over the entire surface, the stone looks lively and shiny. However, for sapphires of darker saturated colors, this is not so important, as the color itself creates a great effect. Opaque dark sapphires are considered the least valuable. To achieve the best color and clarity, sapphires, like rubies, are often heat treated.
A rare and unusual small sapphire weighing 1–2 carats can be unique, so it can be difficult to find a matching stone for it. Low-grade 1000-carat sapphire is of little value as a jewel
Padparadsha is the rarest of the fancy sapphires. It has a pinkish orange color (lotus color). Its cost is equivalent to blue sapphires.
The best sapphires are mined in Kashmir. They are also produced in Madagascar, Cambodia, Thailand, USA, China, Sri Lanka, Australia and Myanmar.
Some corundums contain small inclusions of the mineral rutile. If the concentration of its fibers is dense enough and they have a certain orientation, the light reflected from them can focus on the surface of the stone, forming white lines in the form of six rays of a star. The resulting optical effect is called asterism. Corundums with this effect are quite rare. Depending on the type of stone, they are called “star ruby” or “star sapphire”. At the same time, they are given a shape with a convex smooth surface without edges.
The industrial demand for abrasives is met by the production of synthetic corundum from bauxite. Synthetic corundum is of high quality and cost effective. Artificial rubies and sapphires are also produced. Through manufacturing processes, large, flawless monocrystals can be produced that are cut to create attractive gemstones. The color of these stones can be adjusted by adding small amounts of chromium, titanium, or another substance.
Special optical effects, such as asterism, can be imparted to stones by adding titanium or another material that crystallizes in the form of needles (for example, rutile). In finished cut stones, these needles appear in the form of lines, giving them a “star” appearance. Artificial stones can be difficult to distinguish from natural stones, even for experts, so they must be marked as synthetic in order to be sold.
Read on for an article on bad breath.