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CUTTING TOURMALINE

Tourmaline is a gem that has grown in popularity over the years because of its wide range of colors. The most popular colors are black, pink, green, blue, but they are commonly found with 2 or more colors in the same crystal. These are called bicolor or tricolor tourmaline and are marvelous for gemstone specimens and cut stones alike.

The common crystallized black tourmaline, called Schorl, is attractive and sought after even though it doesn’t have any clarity. The reason schorl tourmaline is opaque is the impurity of tourmaline’s crystal structure. Don’t get scared off by its chemical structure (Ca,Na,K,[vacancy]) (Li,Mg,Fe+2,Fe+3,Mn+2,Al,Cr+3,V+3)3(Mg,Al,Fe+3,V+3,Cr+3)6 ((Si,Al,B)6O18) (BO3)3(OH,O)3 (OH,F,O) -  most of this just means it can have a variety of different forms which will take on different colors.  Tourmaline grows in a prismatic, six-sided crystal. Unlike beryl’s flat termination and quartz which has six-sided point,   tourmaline usually terminates in a trigonal crystal point. All three have similar hardness 7-7.5 on the Mohs scale, so this three faced termination and tourmaline’s typical vertical striations are its key identifying features. Thanks to its relatively high hardness, luster and clarity combined with bright colors, tourmaline is definitely a gem you should add to your collection.

Cutting  tourmaline  can be very tricky, although extremely rewarding with enough foresight. The biggest mistake amateur facet cutters make starts with them buying tourmaline with what we call a “closed c-axis”.  If you look down the top of a tourmaline crystal you will either see a strong, juicy looking color (open c-axis)or an almost black opacity (closed c-axis). Attempting to cut a closed c-axis requires a tourmaline cut, which is very elongated and generally the stone will appear dark, almost black, unless backlit. On the contrary, faceting an open c-axis crystal will result in a stunning, intense combination of all colors present in the crystal. If presented a flawless piece of open c-axis faceting rough, one should consider how to maximize color and size, while also reaching its ideal angle, or “critical angle”, to produce the best gem.

An extremely unique variety of tourmaline is Watermelon Tourmaline, where  the core of a crystal is one color and is surrounded fully by another color (the name coming from green surrounding pink). These watermelon crystals are sliced very thin and polished on both the top and bottom using a flat lap to create “watermelon tourmaline slices”.

Tourmalines have not always been regarded as such a popular gem. The rarest variety is a Caribbean blue, copper-bearing tourmaline called Paraiba. It was first discovered in Paraiba, Brazil and immediately sparked international attention. Various smart investors jumped on this material when it was very cheap ($500 per carat). Today, tourmaline from this location goes for up to $10,000 per carat. Similar color tourmaline from Nigeria and Mozambique  are often called Paraiba but lack the intensity of color, even though they do contain copper.