Zoisite is the mineral that makes up tanzanite. It is gentler than sapphire, with a Mohs scale hardness of 6-6.5, and its coloration is more purple.
Instead, tanzanite specimens are primarily displayed as collectibles. The hue and saturation vary depending on the viewing angle.
The most valuable tanzanite stones are those that are naturally dark blue and have not been heated to enhance their hue.
The most sought-after blue gemstone is sapphire, the blue variety of the mineral corundum.
While blue is the most prominent color of sapphire, other colors exist and are commonly referred to as "fancy sapphires."
The saturation and intensity of a sapphire's color largely determine its value. The greater the gemstone's blue hue, the greater its value.
The only distinction between the two is the presence of impurities in the mineral, which modifies its color and chemical composition.
Natural rubies are significantly more valuable than synthetic rubies, and when polished, some exhibit a star-like light refraction.
The greater the value of a ruby, the greater its size, clarity, and hue.