Information For precious and semi precious gemstones
Stone : Tourmaline
Moh's Hardness : 7 - 7.5
Origin Locations : Minas Gerais, Brazil; Nigeria, Tanzania, Mozambique, Zambia, Namibia, Africa; Madagascar; California, Maine, USA; Elba; Burma; Afghanistan; Pakistan; Mount Painter (Flinders Ranges), Kangaroo Island, Australia
Treatments : None, Heating, Irradiation
Clarity : Eye Clean to Included
Color : Various
Verdelite = Green in all shades
Schorl = Black (often used for mourning jewelry)
Rubellite = Pink to red
Indicolite = Blue in all shades
Paraiba = Caribbean blue, copper bearing tourmaline... very rare!
Dravite = Yellow to Brown
Achroite = Clear to colorless
Cleavage : Indistinct
Chemical Composition : Various
Refractive Index (RI) : 1.614 - 1.666
Density : 2.82 - 3.32
Birthstones : Tourmaline is the birthstone for October.
Tourmaline is the stone for the 8th anniversary
Comments : Tourmaline is a gem that comes in almost every colour imaginable and often in breathtaking combinations. It is thought that the Dutch, importing it from Sri Lanka to Europe in the early 1700's gave it the Sinhalese name, Turamali, meaning "stone with mixed colors". Gems with two or three colors are much sort after, such as blue/greens, mint greens/clear, pink/greens and gold/red. For example, a certain mixture of colours is called watermelon tourmaline where, cut in a cross section, the outer rind appears green whilst the inside is pink. Pinks (intense hot pink and light bubblegum pink), reds and blues are the most desired colors. Some tourmaline gems are treated in order to improve their colour.
In the last 20 years tourmaline has gained great popularity among gem collectors and the gem buying public because of its beauty, availablity and myriad colors. It cuts a stunning gem and suits almost all design styles. Fine examples of tourmaline can be obtained in relatively large sizes though 2 - 10 carats is a popular size range. Tourmaline often has inclusions and eye clean gems are the most desirable. Tourmaline forms as beautiful long crystals and are a great favorite among mineral specimen collectors. This stone can also be found in alluvial deposits as water worn nodules.
A curious property of tourmaline is that when heated and cooled, or by applied pressure, it will become electrically charged (pyro and piezo electricty). The charged stone can attract pieces of paper and dust. It was also used to pull ash out of meerschaum pipes by the Dutch who understood this property of tourmaline. They called tourmaline "aschentrekker" (ash puller).
One thing that can affect the colour and arguably the "quality" and price of a tourmaline gem is if it has what's called a closed "C" axis. What does this mean? Well, given a tourmaline crystal in its original shape, if you look down the crystal (as if you were looking down a metal pipe) and it appears black or very very dark, this tourmaline is said to be "closed", like pulling a curtain across a window. If you can clearly see down the crystal even though the colour may change slightly, eg. a pink tourmaline might look peachy down the "C" axis, it is said to be "open". When a tourmaline with a closed "C" axis is cut, the resulting gem will in all likelihood appear darkish, especially around the ends if it is a rectangluar design. All things being equal, an "open" gem should demand a higher price then a "closed" gem. You can see an example of an open "C" axis tourmaline in the rough here.