Mineral focus: rutile

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Rutile is a metallic-grey to earthy-red, brown, violet or black mineral, largely composed of titanium dioxide (TiO2). It is the most naturally occurring form of this particle and has among the highest refractive indices of any known mineral. It also has a hardness rating of 5.5 to 6.5. Apart from titanium dioxide, rutile is usually made up of about 10% iron, and large amounts of niobium and tantalum. The word ‘rutile’ comes from the Latin word ‘rutilus’, meaning ‘ruddy’, and refers to the deep red colour seen when viewed under transmitted light.

The mineral is usually associated with igneous environments where plutonic igneous rocks are present, since it is formed in very high temperature and pressure conditions. It is also found in extrusive igneous rocks that originate from a deep source, such as kimberlites and lamproites, and also in altered igneous rocks, including certain gneisses and schists.

Rutile is widely used as a welding electrode for the production of titanium metal, but is also used in paints, plastics, paper, foods and in other products as a pigment that require a brilliant white. Rutile is mined only in certain areas of the world. One of the most mined locations is in Sierra Leone, West Africa, which provides 30% of the world’s annual supply. It is estimated that there are 19 years of supply left at this location.

A further use of rutile is its ability to absorb nano-sized particles of UV light. Therefore, it is widely used in sunscreens to protect against UV induced skin damage.

Synthetic rutile was first produced in 1948 and is sold today under various names. It can be produced in various colours, with its purest form being transparent. This colourless type has a high refractive index, giving it a similar appearance to diamonds and is more widely known as ‘titania’. In spite of this similar appearance, it is rarely used in jewellery, since it is very weak and can scratch easily.

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