A Ruby is a red variety of the gemstone corundum, the color caused mainly by chromium. Rubies are the birthstone for people born in the month of July. They are mined in Africa, Asia and Australia. They are most often found in Burma, Sri Lanka and Thailand, though they have also been found in Montana and South Carolina; rubies are exceptionally rare, though artificial ones can be produced. "Ruby" lasers operate with a corundum lasing medium.
Rubies are valued according to several characteristics including size, colour, clarity and cut. All natural rubies have imperfections in them. On the other hand, artificial rubies have no imperfections. The fewer the number and the less obvious the imperfections, the more valuable the ruby is - unless there are no imperfections (i.e. a "perfect" ruby) - then it is suspected of being artificially made and is therefore no longer a priceless gem.
Ruby characters are sometimes used in the typography of ideographic languages, especially Japanese. They are small characters placed above or to the side of an ideogram (kanji in the case of Japanese) that the reader may not recognize, providing its phonetic equivalent. Ruby annotations are used frequently in instructional books and books for children. Ruby characters are also known as furigana outside of publishing circles.