A few elements like carbon, sulphur, gold and noble gases, occur in free state while others are found in combined forms in the earth’s crust. Elements vary in abundance. Among metals, aluminium is the most abundant. In fact, it is the third most abundant element in earth’s crust (8.3% approx. by weight). It is a major component of many igneous minerals including mica and clays. Many gemstones are impure forms of Al₂O₃. For example, gems ‘ruby’ and ‘sapphire’ have Cr and Co respectively as impurity. Iron is the second most abundant metal in the earth’s crust. It forms a variety of compounds and their various uses make it a very important element. It is one of the essential elements in biological systems as well.

For obtaining a particular metal, first we look for minerals which are naturally occurring chemical substances in the earth’s crust and are obtained through mining. Out of many minerals in which a metal may be found, only a few are viable to be used as source of that metal. Such minerals are known as ores.

What is the formula of magnetite?

Fe₃O₄

The correct answer is option 4.\(Fe_3O_4\).

Magnetite is a type of iron oxide mineral with the chemical formula \(Fe_3O_4\). It is a naturally occurring magnetic mineral and one of the most common iron ores. The name "magnetite" is derived from its strong magnetic properties.

The chemical formula \(Fe_3O_4\) indicates that each unit of magnetite contains three iron \((Fe)\) atoms and four oxygen \((O)\) atoms. The ratio of iron to oxygen in magnetite is \(3:4\). This differs from other iron oxide minerals like hematite \((Fe_2O_3)\) and wüstite \((FeO)\), which have different ratios of iron and oxygen.

The crystal structure of magnetite consists of two types of iron ions: \(Fe^{2+}\) (ferrous iron) and \(Fe{3+}\) (ferric iron), arranged in a crystal lattice along with oxygen ions. This unique structure gives magnetite its characteristic magnetic properties, as the arrangement of iron ions allows it to become permanently magnetized.

Magnetite is commonly found in igneous and metamorphic rocks, as well as in hydrothermal veins and some sedimentary rocks. It often occurs as octahedral or dodecahedral crystals, but it can also form massive or granular aggregates. Magnetite is an important source of iron and is used in various industrial applications, including as a pigment, in magnetic recording media, and as a heavy aggregate in concrete. Additionally, it has significant uses in environmental remediation and water filtration due to its magnetic properties.