Tanzanite is a versatile gemstone that comes in a variety of sizes and cutting styles. Although once considered only as an alternative to sapphire, it has quickly established itself as one of the premier gemstones in the world.
In tanzanite, the most-prized color is a pure blue, similar to fine sapphire, or an intense violet-blue all its own. Tanzanite with a bluish purple bodycolor is also popular, but less valuable. In any shade, pale colors are less prized than saturated ones.
Tanzanite is a pleochroic gem, which means it can show different colors when viewed in different crystal directions. This makes cutting a crucial element in determining the color the consumer sees when the stone is cut and set in jewelry.
In some exceptional tanzanites, the color is predominately an intense violetish blue with red flashes of pleochroic color coming from within the stone.
Untreated, tanzanite is typically brownish. Most blue tanzanites for sale today owe their color to heat treatment, which is what reveals its attractive pleochroic blues and violets. The blue crystals originally discovered by Masai tribesmen were an exception because they’d probably been exposed to a natural heat source within the earth at some point.
Much of the tanzanite sold for jewelry has inclusions that can be seen only under magnification, so any eye-visible inclusions cause a drop in value. Also, any inclusions that might pose durability problems, such as fractures, lower tanzanite value greatly.
Cutting plays an important role in tanzanite’s color display. Because of its pleochroism—the ability to show different colors when viewed in different crystal directions—cutting direction determines the gem’s overall face-up color.
But this decision must be balanced against the higher per-carat price that the finer blue or violetish blue color might bring. The cutter essentially makes a choice between a smaller top-color gem and a larger bluish purple one.
Tanzanite is available in a wide variety of sizes, shapes, and faceting designs. The finest and deepest colors are usually seen in sizes over 5 carats. Smaller stones are often less intense in color.