Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al2O3) with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. It is typically blue, but natural “fancy” sapphires also occur in yellow, purple, orange, and green colors; “parti sapphires” show two or more colors. Red corundum stones also occur, but are called rubies not sapphires. Pink-colored corundum may be classified either as ruby or sapphire depending on locale. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Sapphire is one of the two gem-varieties of corundum, the other being ruby (defined as corundum in a shade of red). Although blue is the best-known sapphire color, they occur in other colors, including gray and black, and they can be colorless. A pinkish orange variety of sapphire is called padparadscha.
Occurrence and Mining
Sapphires are mined from alluvial deposits or from primary underground workings. Commercial mining locations for sapphire and ruby include (but are not limited to) the following countries: Afghanistan, Australia, Myanmar/Burma, Cambodia, China, Colombia, India, Kenya, Laos, Madagascar, Malawi, Nepal, Nigeria, Pakistan, Sri Lanka, Tajikistan, Tanzania, Thailand, United States, and Vietnam. Sapphires from different geographic locations may have different appearances or chemical-impurity concentrations, and tend to contain different types of microscopic inclusions. Because of this, sapphires can be divided into three broad categories: classic metamorphic, non-classic metamorphic or magmatic, and classic magmatic. Sapphires from certain locations, or of certain categories, may be more commercially appealing than others, particularly classic metamorphic sapphires from Kashmir, Burma, or Sri Lanka that have not been subjected to heat-treatment.
The most important characteristic to consider when determining a sapphire’s price is always its color grade. The best color for a natural blue sapphire is an intense, velvety, deep royal blue. This color of sapphire would be considered AAA quality, the rarest and most valuable. The second best color is a medium rich blue, or AA quality. Any blue sapphires that have a slight gray undertone fit into the A category. Finally, sapphires that have a very dark and opaque blue color are considered B quality grade. The 3 keys to color grading are identifying hue, tone and saturation. Color is graded on these factors face up on a white surface. The hue should be royal blue, the tone should be deep blue and the saturation should be even throughout the gem.
In terms of weight, sapphires are weighed the same way that diamonds are. The higher the carat, the more expensive the sapphire will be. Larger sapphires automatically have a higher carat weight, so they will always cost more.
Typically blue, but varies
As crystals, massive and granular
Both growth twins (in various orientations) and polysynthetic glide twinning on the rhombohedron
Mohs scale hardness
Transparent to nearly opaque