LEPIDIOLITE

A silicate which may be pink, purple, white or colourless. It is a mica which appears in sheet like layers. Its name is derived from the the Greek word lepis, which refers to the flaky appearance of many specimens. It is also known as lithia mica.

Due to its softness (2.5-4 on the mohs scale) it cannot be used for jewellery or ornaments but is popular with mineral collectors due to its beautiful appearance. However, it is a major source of the mineral lithium and is also used in the manufacture of alloys and batteries.

It is one of the few minerals that contain the mineral rubidium. This enables it to be useful for scientists in determining the age of the surrounding rocks. By calculating the rate at which the isotope rubidium-87 decays into the isotope strontium-87 scientists can calculate the rocks approximate age. This method is known as rubidium-strontium dating and is very useful for geologists.

It forms in igneous rocks particularly granite and pegmatites. It may be found in association with spodumene and tourmaline and in veins that are rich in tin.

Lepidiolite can be found in Canada, Czech Republic, Italy, Japan and California and Colorado (US).

MAGNEITE

An oxide with a dull or metallic sheen which is shiny black in coulour. It is a member of the spinel group of minerals and is magnetic as its name suggests. There are several varieties of magnetite which differ slightly in composition and form the magnetite series e.g. franklinite, jacobsite and trevorite. They may contain impurities and may only be able to be differentiated by detailed scientific analysis.

It is moderately hard (5.5-6.5 on the mohs scale) and is an industrial source of iron along with limonite and siderite. Iron is extracted in a furnace by a method known as chemical reduction. Carbon monoxide and hydrogen are passed over the mineral and a chemical reaction takes place. Carbon dioxide is extracted and pure iron is left behind. Iron is very useful industrially as it is a good conductor of electricity. Iron compounds are often used to make paint pigments.

Magnetite can be found in many rock types. It sometimes occurs as an accessory mineral in igneous rocks as well as in the veins of metamorphic rocks.

The largest deposits are in Sweden. It can also be found in Austria, Italy, Ural Mountains Russia, South Africa and USA.