Tourmaline occurs in many colours and also in combinations of two or three different colours. The colours can be at different ends of the mineral or together in the heart of it.  A gemstone with a pink centre and green border is known as watermelon tourmaline.

An electrical charge can be induced in some crystals and this effect has found many uses in pressure measuring equipment and other scientific applications.  This mineral was used in the production of pressure sensitive gauges for submarine instrumentation and other war-time equipment.  The pressure gauges that measured the power of the first atomic bomb blasts, were made with slices of tourmaline.

In crystal healing, tourmaline is used to enhance understanding, increase self-confidence, amplify psychic energy and as an aid for concentration and communication.  It is also believed to neutralize negative energies, dispel fear and grief and aid relaxation of both the mind and body.

Found in Africa, the Ural Mountains of Russia and other European locations, some of the most exciting finds have been in North and South America.  Some of the most beautiful specimens were discovered early in the 19th century in the United States and in 1972, a mine in Maine established itself as one of the largest ever found.  For a brief period it became a world source for superior quality red and green coloured tourmaline.  The first pink stone was found in the 1860's in San Diego.  Today the largest mines are in the Minas Gerais state of Brazil but it can also be found in Kenya, Madagascar, Nigeria, Mozambique, Myanmar, Russia, Namibia, Afghanistan, Pakistan and Sri Lanka.

Graded 7 to 7½ on Mohs scale of mineral hardness, tourmaline along with opal are the birthstones for the month of October.

Further Reading:
Tourmaline by Wikipedia
Gemology Online - tourmaline