This is a faceted rondelle shape shades of blue Iolite beads strand. 13" strand about 130 beads, about 3mm sizes, sizes vary slightly; Genuine and natural; micro faceted machine cut glittering clean transparent clarity; quality suitable for fine jewelry making; use 0.012" wire or cord and 28 gauge wire; Iolite should not be cleaned in ultrasonic or steam cleaners. It is safe to clean iolite with warm soapy water, but avoid abrupt changes in temperature. Iolite is typically light to dark blue or violet-blue, but it may also occur in light shades of yellow, green, gray, or brown. Iolite is strongly trichroic, meaning that it shows three colors when viewed from different angles. Violet-blue iolite is considered ideal color. A cube-shaped piece of iolite can appear blue from one angle, clear from another, and surprisingly golden from another. Iolite is the gem-quality blue or blue-violet variety of cordierite. While iolite enjoyed popularity in jewelry in 18th-century Europe, this naturally beautiful gemstone is relatively new to the jewelry market and is regaining popularity with the public. Because of its hardness and pleochroism, iolite is one of the most difficult stones to cut. It must be cut in a certain direction to take advantage of the best color, which can be tough when the shape of the rough doesn't lend itself to cutting in that same direction. Iolite is sometimes referred to as "the Viking stone" because, according to Norse legend, Vikings used thin slices of iolite as polarizing filters, allowing them to look directly at the sun and use its exact location in the sky to navigate the open seas. If this is true, it would help explain how the Vikings supposedly managed to travel such great distances across massive expanses of ocean without modern navigational aides.