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SEDAGEMS

TOURMALINE BIRTHSTONE FOR OCTOBER.

   This is a pair of well polished stones ready for setting.These stones were cut from the same piece of rough but there is a small difference in size.

NATURAL STONE UNTREATED

CABACHONED

MINED IN BRAZIL 

MOHS SCALE 7-7.5

WEIGHT 42.40   CTS APP

 SIZE   24X17X5 MM APP

Often, Nature conjures up tourmaline crystals from which gemstones with a particularly subtle multi-colouredness can be cut. You may well ask how that is possible. Tourmalines are mixed crystals of aluminium boron silicate with a complex and changing composition. It's a rather complex mineral group. Even minor changes in composition cause completely different colours. And that is how, on one and the same crystal, although it has grown quite naturally, completely different colours can occur, mostly in elongated columns one above the other, as if Nature had piled coloured rings one on top of the other. The crystals themselves can be as slim as a knitting-needle or as thick as a man's thigh. Some display coloration in which the shades vary only slightly, whilst others have starkly contrasting colours or zones of colour. Since tourmaline crystals have often grown in close proximity to one another, their cross-sections can also contain triangles which are closely joined together and gathered around a nucleus.

Stones with two or more different, well represented colours are particularly desirable. Depending on their shape and colour, these are known in the trade as bicoloured and multicoloured tourmalines respectively. Some of them also have rather interesting names: if, for example, the crystal is almost colourless and just black at both ends, it is referred to fondly as a 'Mohrenkopf', (a kind of cake popular in Germany). If it was red at one end it used to be called a 'Turk's head tourmaline'. Bicoloured tourmalines with a red centre which changes to green towards the edges are still referred to as 'watermelons'. If the colour zones of the crystal lie on top of one another, the Brazilians call it a 'papageios' or 'rainbow tourmaline'.

The main deposits of tourmalines are in Brazil and Africa. But Nature has also made Man a gift of this beautiful gemstone, always good for a surprise on account of its great diversity of colour, at other deposits, for example in Sri Lanka and Madagascar.

Pure individuality

Tourmalines are popular not only in jewellery but also as therapeutic stones. Thanks to their good energetic conductivity and their wealth of minerals, they are said to have an invigorating and fortifying effect. They are uncomplicated to work with and have excellent wearing qualities thanks to their good hardness. Beautiful multi-coloured tourmalines are particularly well suited to jewellery of an individual design, for each of these stones is different. More than that, indeed: practically each of the places where this gemstone is found - and it occurs all over the world - has its own colour variant. That does make life somewhat difficult for the cutter if he has to look for several stones of the same colour; in fact even two stones cut from the same raw crystal often differ in colour. But then that is the charm of the tourmaline, and especially that of the multi-coloured tourm

 Tourmaline is a crystal silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline gem stones come in a wide variety of colors.Tourmaline has a variety of colors. Usually, iron-rich tourmalines are black to bluish-black to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are almost any color: blue, green, red, yellow, pink etc. Rarely, it is colorless. Bi-colored and multicolored crystals are common, reflecting variations of fluid chemistry during crystallisation. Crystals may be green at one end and pink at the other, or green on the outside and pink inside: this type is called watermelon tourmaline. Some forms of tourmaline are dichroic, in that they change color when viewed from different directions.