Sapphire

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. The only color that corundum cannot be is red (as red colored corundum is called ruby).

Formation & Geology

Like rubies, sapphires form in metamorphic and igneous environments. The blue color is typically caused by charge transfer between iron and titanium ions. Sapphires are found in alluvial deposits where they have been weathered from their source rocks, as well as in primary deposits like pegmatites and basalts. The Kashmir region is historically famous for the velvety blue sapphires found there.

Physical Characteristics

Sapphires are among the most durable naturally occurring elements in the world. With a Mohs hardness of 9, they are suitable for everyday wear in jewelry. Sapphires often exhibit 'color zoning', with light and dark bands of color. Some stones contain microscopic rutile needles that create a star effect, known as Star Sapphires.

Historical Significance

The name sapphire is derived via Latin 'sapphirus' from the Greek 'sappheiros', which meant blue stone (though likely referred to Lapis Lazuli at the time). Sapphires have long been associated with royalty and romance. The British Crown Jewels contain many large sapphires, and Prince Charles gave Lady Diana a sapphire engagement ring (now worn by Princess Catherine).

Colors & Varieties

While blue is the most famous color, sapphire occurs in every color of the rainbow except red (which is ruby). The rarest and most valuable variety is the "Padparadscha" sapphire, a delicate pink-orange stone named after the lotus blossom. "Color-change" sapphires shift from blue in daylight to purple in incandescent light. "Parti-colored" sapphires show two or more distinct colors in a single stone.