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.
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.
turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminum. turquoise has a lower-than-ideal hardness and durability for use in certain types of jewelry.