I was watching DSN this morning and saw they had natural color tanzanite. The shades of the stones offered ranged greatly from greenish/brown, green/blue, blue/green, some had a bit of purple. All deep purple/blue tanzanite has been treated , right? I thought I read that tanzanite comes out of the earth brown, but do some have bits of green, blue and or purple naturally? The stones were pretty light in color. Has anyone seen this in person?
tanzanite is the violettish blue variety of zoisite, which in its unheated state is that greenish-brownish. It is POSSIBLE for zoisite to be 'heat-treated' by mother nature, but that isn't what you usually run across. I also don't know of the tests to determine if humans or mother nature did the heating...I don't know that there is one to verify 'natural tanzanite' color...maybe in the big labs. Anyone know?
Originally posted by GemGoddess tanzanite is the violettish blue variety of zoisite, which in its unheated state is that greenish-brownish. It is POSSIBLE for zoisite to be 'heat-treated' by mother nature, but that isn't what you usually run across. I also don't know of the tests to determine if humans or mother nature did the heating...I don't know that there is one to verify 'natural tanzanite' color...maybe in the big labs. Anyone know?
I don't know about the test either...I doubt anyone's tried to develop one because there's little demand for it.
In its natural state zoisite can be pink (thulite), gray, yellow, brownish, brownish-yellow, colorless and green. Only certain types of zoisite can be heat treated to change color. I have a friend who cut some of the green and called it "Green Tanzanite," and I've seen "Pink Tanzanite" advertised. Both names seem misleading to me because the name "Tanzanite" was originally given to the purple to blue material by Henry Platt, vice president of Tiffany and Co. in honor of Tanzania, the only place it's produced to date. (I keep hearing rumors of tanzanite from Madagascar but can't pin them down).
In its natural state zoisite from Tanzania is grayish to root beer brown. I've heat-treated a fair amount of it and in my experience the darker the brown the more intense and deeper the blue or purple color. Because tanzanite is trichroic (3 different colors when viewed from different directions) crystals can yield either pure sapphire blue cut stones or the more common purplish to violet-blue. That's because the cutting direction for pure blue (considered the most valuable) is usually the direction of lowest yield. Most cutters opt for the higher-yielding purplish hues.
Tanzanite's color can be changed from brown to blue tones by natural sun heat or brushfires, etc. if exposed on the ground's surface. In 1969 a Masai warrior brought a 10,000-carat chunk of transparent purplish-blue tanzanite to a gem buyer in Nairobi. At that time it was a virtually unknown gemstone and the buyer turned it down thinking it was glass. The asking price was $50. Now the disgruntled buyer thinks it might have cut a gem larger than the 220-carat stone now on display at the Smithsonian.
"Tanzanite is trichroic with brown, blue, and purple colors in different directions, and sometimes one color can predominate over the other two.
We don't heat any of our tanzanite specimens, although the miners
themselves do sometimes heat tanzanite pieces if they think it will
increase the value by removing some or all of the brown color component.
It is safe to guess that tanzanite with no brown color component has
probably been heated."
Sunstone- DSN is a gemstone and jewelry shopping channel on satellite tv.