𝐓𝐇𝐄 𝐏𝐑𝐄𝐂𝐈𝐎𝐔𝐒 𝐆𝐄𝐌𝐒𝐓𝐎𝐍𝐄 𝐑𝐔𝐁𝐘
The color of Ruby ranges from bright red to dark reddish-brown. The most preferred color is a deep blood red with a slightly bluish hue. Such Ruby is known as "Burmese Ruby" or "Pigeon's Blood Ruby". Ruby from Burma is famous for its exceptional coloring, and has traditionally produced the finest Rubies. However, Burmese Ruby rarely exceeds several carats; large flawless Burmese Rubies can be worth millions of dollars. Many Rubies on the market are from Thailand, and these Rubies have a less-desirable brownish hue, though they often can be heat treated to improve color. Heat-treating a Ruby can also increase its transparency by removing tiny internal flaws.

Inclusions of tiny, slender, parallel Rutile needles in Ruby cause a polished gem to exhibit asterism. A Ruby displaying asterism is known as a "Star Ruby", and if transparent can be very highly prized. Star Rubies exists in six ray stars, though twelve ray stars are also known. Rubies must be have good transparency to possess gem value. Opaque or semi-opaque Rubies have relatively little value, even if they display asterism.

The same Rutile inclusions that are responsible for asterism in certain Rubies can also decrease transparency and cause a hazy effect known as silk. Though Ruby can be one the most expensive gemstones, it also comes in more dull opaque forms that are fairly inexpensive, and are often polished into cabochons. A unique gemstone form composed of opaque red Ruby in contrasting green Zoisite is well known from Tanzania, and is used as a minor gemstone and can be carved into ornaments.

The color of Ruby is usually caused by minute inclusions of the metal chromium. These impurities are often responsible for causing a Ruby to fluorescent, which can be helpful in its identification. Ruby is also pleochroic, and will sometimes display a lighter and more intense color when viewed at different angles.

Ruby is a tough and durable gem, and the only natural gemstone harder than Ruby is Diamond. Despite this, Ruby is still subject to chipping and fracture if handled roughly, and care should be taken to ensure it is properly handled.

Ruby was first synthesized in 1902. The process of creating synthetic Ruby is known as the Verneuil process. Only experts can distinguish between natural and synthetic, lab-created Ruby.