The mineral magnetite is iron oxide (Fe3O4), which is found in all three igneous, metamorphic and sedimentary rocks. This stone is often extracted from iron ore. Magnetite is also a mineral with the highest amount of iron (72.4%).
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.