Is This Really Good Turquoise? Who Knows?

With its palette of sky, water, earth and trees, turquoise has been traded and worked and worn throughout history and across cultures.

But what makes a good turquoise stone? The answer is not always clear.

In diamonds, the Four Cs (color, clarity, cut and carat weight) are an accepted industry standard for determining quality. In the world of faceted gemstones such as sapphires, rubies or emeralds, aspects of color — hue, tone, saturation — take center stage.

When it comes to turquoise, though, opinions tend to be all over the map — much like the mineral-rich opaque stone itself, which can be monochromatic or variegated, clear as a cloudless summer sky or laced with a spiderweb pattern of host rock, or matrix. Preferences have varied by region and change over time.

Then there is the source of the stone. Passionate collectors often seek turquoise from specific mines, many of which are no longer in production.

The scarcity of high-quality natural turquoise has been driving up prices — a rare stone from a classic mine may cost 25 to 30 times what it did 25 years ago, experts say — but there is no widely accepted standard to determine what makes one stone better than another.