The ‘gemstone of the rainbow’ certainly lives up to it’s name. Tourmaline has the most variation of colour of any gemstone with a staggering array of colours avaliable from one mine and often bicoloured or multicoloured stones.

Ranking a 7 to a 7.5 on the moh scale of hardness they are excellent wearing with and there wide variety of colours has made them a very popular gemstone for jewelery with many designers using them due to the inherent versatility of the gem. They are mined in many places across the world and what is interesting is that according to locality the colour of the Tourmaline will often often change. Yellow or ‘canary’ Tourmalines are prevalent in Malawi while in Paraiba in Brazil they are famed for their intense blue and blue-green stones.

The massive amount of variation within the trade leads to problems when trying to tie price to an invariant figure. As with all gemstones Tourmaline is priced due to rarity and while as a stone it is not hugely rare the individual variations can increase the price substanstially.

However, they are not just interesting in terms of apperance, in terms of physical science they are interesting gems also. They exhibit pyroelectricity which means that when heated and allowed to cool they will temperily emit electricity and create a voltage. Scientists are not completely sure how Tourmalines do this, because although they know the crystal structure is changed in heated the exact mechanics are not currently known.

Moonstone is a variety of feldspar which is the most common mineral in the earth’s core. It is technically a sodium potassium aluminium silicate and is characterised by it’s adularescence (it’s shine as light moves through it).

The shimmer of colour as light moves through it is due to the different layers of feldspar that make up it’s internal structure. These layers have different refractive indexs and therefore they slow light at different levels which creates refractioned light through one which is then refracted again through the other layers.

It is commonly mined in Australia and Sri Lanka but there have been numerous deposits of moonstone found the world over. Furthermore, it is not a new gemstone, there are records that show it was around during the age of the Romans, where they believed it was created by frozen moonlight. Although not a particuarly rare stone it is nonetheless a beautiful one and when cut into cabochon shapes they become very popular jewelery pieces.

With a rating of 6.5 on the moh scale they are hard enough to withstand some wear but they can easily be chipped or scratched so care must be taken when wearing one to not expose it to too many extrememe conditions.

Opal is a relative of quartz but is itself not a mineral, it is a mineraloid due to it’s lack of crystalisation. 97% of opal is mined in Australia, where it is the national gemstone. Prized for their ability to display every colour of the visible light spectrum.

The reason for opal’s incredible refraction ability is due to it’s structure. Silica spheres arranged in planes, or rows, that taper to a pyramid shape, the spacing and posistioning of the planes, in response to the angle of refraction determined by the appropriate angle of incidence, that causes the dispersion of light leading to incredible refraction. To give you an idea of how well light is refracted in opal, opal’s refractive index is 1.45 which means that in a vacuum light travels 1.45 times faster than it does in opal, (as a point of reference, water’s refractive index is 1.33).

Clarity is difficuilt to measure in opal due to the extreme commonality of ‘veins’ within opal which instead of being seen as a disadvantage are essential to the distinctive light performance that makes opal’s so sought after. Instead opal’s are ranked either translucent, semi-translucent or opaque. Opal’s are often treated, commonly with oils, and this is one of the main reasons that they cannot be placed in an ultrasonic cleaner. The other is the porous quality of opal (some opal’s can be 30% water), means that the cavatation process used in ultrasonic cleaning would shatter the opal.

In terms of cut, a cabachon cut is usually used, to avoid abrasion and enable the best range of light play through the opal. Although this can still be used in it is different to the usual apperance. But that could be perfect.