July birthstone: ruby

How to read it

Ruby has been the July birthstone since 1912. Rubies and sapphires are the same mineral, corundum: red corundum is ruby, and every other colour is sapphire. GIA says ruby takes its colour from traces of chromium, the more chromium the stronger the red, and that the trade calls the finest colour, a deep red with a hint of purple, “pigeon’s blood”. Ruby is the traditional gem for the 15th and 40th wedding anniversaries.

Also searched as: birthstone for July, ruby birthstone.

Why ruby is July's stone

Before 1912, ruby was often given to December. The list adopted that year moved ruby to July and turquoise to December, a change George Kunz recorded in 1913 and disagreed with. In the eight older lists Kunz compared, onyx was July’s stone in five.

Where rubies are mined

GIA names the Mogok area of Myanmar, which has produced rubies for more than five centuries; Vietnam since the late 20th century, in the Luc Yen region and the Quy Chau district; and the Montepuez mines of Mozambique. For many years in the late 1900s the deposits along the border between Thailand and Cambodia were the main source.

Ruby or red spinel

GIA says red spinel was mistaken for ruby for centuries, and was not clearly told apart from it until the 18th century, by their chemical differences. The Black Prince’s “ruby” in Britain’s Imperial State Crown is a spinel. Spinel is now one of the August birthstones.

Treatments

GIA says rubies are often heat treated to remove purplish colour, and that the trade generally accepts this. In lower-quality stones, fractures and cavities that reach the surface may be filled with glass. GIA notes that the Federal Trade Commission requires treatments that affect a gemstone’s perceived value to be disclosed.