agate is a common stone formation, consisting of chalcedony and quartz as its main components, consisting of a wide variety of colors. agates are primarily formed within volcanic and metamorphic stones.
Alexandrite is known as "Emerald by day, ruby by night" because it has one of the most dramatic color changes among gemstones, such as green in sunlight and red in incandescent light. The very precious habit of alexandrite color change is caused by the presence of minor impurities in the element chromium. The most desirable Alexandrite colors are those that have a very clear color change.