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.
Hematite is one of the most abundant minerals found on the earth's surface and in shallow crust. Hematite is a type of iron oxide with the chemical composition Fe2O3. This rock is a common rock-forming mineral that is often found in sedimentary, metamorphic and igneous rocks.
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.
