Gem-quality iolite can vary in color from sapphire blue to violet-like blue and from light-blue to yellowish-gray. Its strong pleochroic properties can often be used to help identify and distinguish iolite amongst other similar colored gemstones. Iolite can sometimes be mistaken for sapphire and tanzanite, but it is softer than sapphire, and harder than tanzanite. Other gems which may also cause confusion include spinel and garnet, but both spinel and garnet are singly refractive, which means they lack iolite's trichroism.Iolite is typically light to dark blue and violet, although it can also occur in various shades of yellow, gray, green or brown. The most desirable color is an intense violet blue that can rival that of tanzanite. Iolite is trichroic which means that three different colors can be seen in the same stone depending on the viewing angle. Some lower grade or poorly cut iolite can appear overly dark or 'inky', often appearing near-blackish.The mineral cordierite is typically opaque, while fine gem-quality iolite appears transparent to translucent in clarity. In many cases, the cutting quality of the gem can affect its clarity. Stones cut too deep may appear opaque. Most iolite exhibits some visible inclusions, especially in larger stones. Although they are rarely encountered, eye-clean specimens are not unheard of. When polished, iolite exhibits an oily to vitreous luster.