Sapphire Overview

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.

Quality Factors

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.

After color, clarity is another important factor that has an impact on a gemstone’s price and rarity. There are three types of clarity grade for gemstones such as sapphires: Type 1 stones, Type 2 stones, and Type 3 stones. •Type 1 stones – These stones will generally be “eye-clean,” meaning that they have no inclusions visible to the naked eye. •Type 2 stones – These typically show some inclusions visible to the naked eye. However, they don’t detract from the overall beauty of the gemstone. •Type 3 stones – These gemstones will almost always have inclusions, and they will always be visible to the naked eye
DThe cut of a sapphire refers to how well the surface is proportioned and polished. If a shallow- or deep-cut sapphire is poorly cut, it will be prone to light leakage. The best cuts of sapphire will always show optimal brilliance. They will look like they have more “life” to them. Sapphires with these cuts are rarer, and they are more expensive than inferior cut sapphires.

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.

Identification

Color

Typically blue, but varies

Crystal habit

As crystals, massive and granular

Twinning

Both growth twins (in various orientations) and polysynthetic glide twinning on the rhombohedron

Cleavage

Poor

Fracture

Conchoidal, splintery

Mohs scale hardness

9.0

Luster

Vitreous

Streak

Colorless

Diaphaneity

Transparent to nearly opaque

Specific gravity

3.98~4.06

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