opal is a hydrated amorphous form of silica. because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classify as minerals.
sapphire is a precious gemstone, a type of the mineral corundum, include of aluminum oxide with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium.
garnets are a category of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. all species of garnets possess similar physical properties and crystal forms, but differ in chemical composition.