Tourmaline can be quite an extraordinary stone in that tourmaline gem material can be of practically any colour from the colour spectrum and, more fascinatingly, a single stone can present up to seven different colours depending on the angle of observation and lighting conditions. It is also a isomorphous replacement stone, which is a technical term meaning that one element within its structure can be replaced by another; either wholly or partially. This results in tourmaline presenting a wide range of physical and optical attributes such as a wide range of refractive index readings or a wide range of specific gravity readings depending on which element was replaced by which other element and to which degree. This can make differentiating tourmaline from other natural gem material difficult as the readings from a particular tourmaline specimen can overlap with the known range of readings from other gemstones.
The most sought-after tourmaline, and thus most expensive, is a blue/green-coloured variety referred to as Paraiba. This has lead to a number of (unscrupulous?; or rather misinformed?) vendors claiming they are selling Paraiba tourmaline. The problem with such claims is that only tourmaline originating from Paraiba, Brazil, can legitimately claim the title to the name Paraiba. To complicate matters further, true Paraiba tourmaline was only successfully mined for about two years some time ago. While the same area in Brazil still produced tourmaline material, it is nowhere near the same quality as the early Paraiba specimens. This extreme rarity translates into extremely high prices. Therefore, anyone claiming to be selling Paraiba tourmaline at somewhat affordable prices is either unaware of true origins of the product he or she may be selling or, more worrisome, is knowingly making a false declaration as to the stone’s pedigree. In any event, as the adage goes: if it sounds too good to be true, it probably is. The it, of course, is the price-point. With the above in mind, much of tourmaline currently found on the market originates from Mozambique, Africa.
Do not let the above detract you from tourmaline; however. There are some beautiful specimens out there that have inherent value in their own right. As with Scotch, forget about brand names and price-points – instead go for taste. In French there is an expression that says: les goûts ne se discutent pas, which basically means that you are not obligated in any way to justify your personal preferences. Everybody likes what s/he like and everybody likes something different. There is no need to focus exclusively on … say, emeralds … when tourmaline can produce an equally stunning, if not also superior, brilliant green stone. If you like the look of a stone, it is worth considering. Do not get too caught up in emerald vs tourmaline vs spinnel, etc.
Tourmaline generally have very good wearability; meaning they are both hard and durable (aka tenacity).
Other Interesting Facts
Tourmalines can easily product static electricity. This means they can easily produce an electric charge if rubbed, heated, or submitted to pressure. They will, therefore, attract small dust particles in the air.
- Technical Details
- Colours: Every colour possible.
- Diaphaneity: Transparent.
- Luster: Vitreous (glass-like).
- Streaks: N/A
- Pleochroism: Pink tourmaline will present a distinct: colorless-pink and pinkish-red combination;
- Orange/brown tourmaline will present a strong yellowish-brown and dark greenish-brown combination;
- Yellow tourmaline a distinct pale yellow and dark yellow;
- Violet/purple tourmaline a strong light purple and purple;
- Blue tourmaline a strong light blue and dark blue; AND
- Green tourmaline a strong yellow-green and dark green colour combination
- This pleochroism is typically less noticeable in lighter coloured stones while more easily observed in darker coloured ones.
- Optical Phenomena: Cat's eye (chatoyancy) does occur but (exclusively? Or predominantly?) in green and pink varieties.
- Some tourmaline produce a colour-change effect; meaning a slight change of colour depending on the lighting conditions.
- Inclusions: Inclusions may or may not be visible to the naked eye. When they are present, they are typically fiber-like structures within the stone. If these fiber-like inclusions are aligned in a parallel fashion to one another, they are responsible for the cat's eye effect that some stones present.
- Optic character and sign: (U-) double refractive, uniaxial, negative
- Refractive Index: lower reading in the 1.614-1.616 range; and upper readings in the 1.652 to 1.666 range
- Birefringence: 0.014 to 0.040 range
- Conoscope image: n/a
- Specific Gravity: 3.85 to 3.35 range.
- Hardness (Mohs scale): n/a
- Tenacity: tenacious – will withstand most normal wear-and-tear
- Spectral Absorption: n/a
- Chelsea Filter Reaction: n/a
- Dichroscope Reaction: n/a
- Polariscope Reaction: n/a*