You’re examining a women’s 14k white gold ring with a beautiful pear-shape, 6.64 ct. stone that’s a slightly grayish, slightly greenish, medium-dark blue not unlike the color of aquamarine. You have only a loupe.

You see rounded facet junctions and make your initial guess: The stone is glass.

You check for inclusions: There aren’t any; the stone is definitely glass.

You look carefully at the culet through a bezel facet. You see two culets, revealing that the stone is doubly refractive. The stone isn’t glass.

You consider the color: It suggests aquamarine or perhaps maxixe, halbanite, or spinel. You remember that spinel is singly refractive—you’d see only one culet through the bezel. The stone isn’t spinel.

You remember that aqua, maxixe, and halbanite are all too hard for facet junctions to become rounded. The stone isn’t aqua, maxixe, or halbanite.

You consider zoisite. The color, while not typical of tanzanite (heated zoisite), is sometimes seen in nonvarietal zoisite.

You buy the ring. You send it to a lab for identification with a refractometer.

You get the results. The stone is . . . ?

Send your best guess to Gary Roskin, senior editor, and win a free gemstone image from the JCK Research and Stock Art Store. The first jeweler to correctly identify the stone will win. E-mail: groskin@reedbusiness.com.