Silver ring with sapphire and 24k gold plating

Sterling silver, gold 24K,  Sapphire 
 Size: 17.2 / US 7 
 Weight: 9.61g 
 Element size: 18.5mm diameter, 8mm height 
 Stone: Sapphire 4mm 
 Ring thickness 3mm 
 
 Sapphire is a type of mineral - corundum. A sapphire is any jewelry-grade corundum crystal that is not red in color (red corundum is called rubies). The most common sapphire is blue. Sapphire-forming corundum is pure in color. The special color is given by various impurities, such as iron, chrome. 
 Iron and titanium are added to the sapphire in various shades of blue. If the crystal has an insufficient amount of such an impurity, it has a light, gray color and a lower value. 
 Yellow and green colors also give an iron admixture. Pink sapphires contain chromium. If there is more chromium, the stone is closer to red and is considered a ruby. 
 Purple, purple corundum has a mixture of vanadium. Such gems are traditionally less valuable. 
 White sapphires (leucosaphires) are most often slightly brownish or yellowish at first. The pure color is obtained by heating them. Pure colorless corundum is very rare. 
 There are also sapphires that change color in different lighting - blue in daylight and purple in artificial lighting.