Ruby is the birthstone for July, the gem for the 40th wedding anniversary.
Rubies can have the highest per-carat price of any coloured stone, even higher than diamonds in the larger sizes. Rubies of over one carat are very rare.
Colour is the most significant factor affecting a ruby’s value. Ruby has a pure, vibrant red to slightly purplish red colour. As the colour becomes too orangy or more purplish, the ruby reduces in value. Fine ruby glows with intense red in sunlight due to red fluorescence, which intensifies its red colour. The highest-quality rubies have vivid colour saturation. If the colour is too dark it reduces the stone’s brightness. Too light and the stone is considered pink sapphire. Rubies have pleochroism, (where different colours can be observed when viewed from different angles) red/purplish to orangy/red in rubies.
Inclusion-free rubies are practically nonexistent. Inclusions that reduce transparency or brightness reduce a ruby’s value significantly. These can be small crystals, zones of colour variation called zoning or banding, or resemble fingerprints.
A ruby’s rough crystal shape dictates its cut. Ruby rough is very expensive, so cutters try to conserve as much weight as possible. The most common shape is a flat tabular hexagonal shape though some longer shapes also occur. Rubies are mainly cut into ovals and cushions, with brilliant-cut crowns, and step-cut pavilions. Round, emerald-cut, square, triangular, pear and marquise rubies are also available. But these shapes are rare in larger sizes and higher qualities. Less transparent rubies are often cut as cabochons or beads. Rubies that have the optical phenomenon of asterism (the star effect caused by the intersection of needle-like inclusions) are always cut as cabochons.