ROCK TRIVIA: RUBY, the birthstone of July
Ruby is red corundum, all the other color varieties of the corundum are called Sapphire. Corundum is the second hardest gem on the Mohs scale, only Diamonds are harder. Ruby is one of the most expensive gems, large rubies are rarer than diamonds.
Rubies range in color and can have a pink, orange, purple or a brownish red tint, depending on the chromium and iron content of the stone. The color of ruby is its most important quality factor. The most sought after color is a strong pure red to red with a hint of blue. This color is called "pigeon's blood". When the color of ruby is very light, it is called pink sapphire, but the line between pinkish-red ruby and pink sapphire varies by definition.
In the picture, a necklace by Van Cleef & Arpels, made in 1938 by Rene-Sim Lacaze for the Duchess of Windsor