Magnetite
Magnetite also known as lodestone or loadstone, is a magnetic mineral form of iron (II, III) oxide, one of several iron oxides. Greyish black or iron in colour, with a metallic appearance and a hardness of 5.5 to 6.The magnetic properties led to lodestones being used as an early form of magnetic compass.
In geology, magnesia is a natural form of magnesium oxide, also called periclase. Stones from the Magnesia region in Ancient Greece, contained both magnesium oxide and hydrated magnesium carbonate as well as iron oxides (such as magnetite). Thus these stones, called Stones from Magnesia in antiquity, with their unusual magnetic properties were the reason the terms magnet and magnetism were coined.