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.
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.
alexandrite is the highly regarded color changing variety of chrysoberyl. the color of alexandrite changes under different lighting conditions. if viewed in daylight, its color is greenish blue to dark yellow-green.