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.
emerald is a gemstone and a type of the mineral beryl colored green by trace amounts of chromium and sometimes vanadium. emerald in antiquity were mined in Egypt at locations on Mount Smaragdus since 1500 BCE.
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.
