Emerald is a variety of the mineral beryl, by trace amounts of chromium and sometimes vanadium. A fine emerald must possess not only a pure verdant green, but also a high degree of transparency to be considered a top gem. Gray is the normal saturation modifier or mask found in emerald; a grayish-green hue is a dull green. Unlike diamond, where the loupe standard, i.e. 10 X magnifications, is used to grade clarity, emerald is graded by eye. Thus, if an emerald has no visible inclusions to the eye (assuming normal visual acuity) it is considered flawless.