Ruby gets its red color from chromium in impurities in its makeup while sapphire gets its blue color from iron and titanium. Ruby must be predominantly red in order to be classified as ruby. If a “ruby” contains too much orange, it is considered an orange sapphire. If a ruby contains too much purple it is considered a purple sapphire. Both orange sapphire and purple sapphire are less valuable than a true ruby which is something to consider when you buy a ruby. The most valuable rubies are a pure red or slightly purplish red with a medium to slightly dark tone. If a “ruby” is too light in color it is actually considered a pink sapphire. The finest and most valuable rubies actually fluoresce red due to the chromium they contain. This means they actually glow red making for a very vibrant red ruby. These rubies are typically found in marble deposits which are very low in iron. Rubies found in basalt deposits typically contain iron as well as chromium which will inhibit the fluorescence of a ruby. Although rubies with iron that do not fluoresce may not be as valuable as those that do, they can still be extremely valuable.