A shimmery stone with unusual properties, kyanite can become the sparkle in a necklace or the spark plug in an engine. This aluminum silicate is a polymorph with andalusite and sillimanite, meaning it shares the same chemistry, but has a different crystal structure. Kyanite is commonly a deep blue, similar to sapphire, and is named from the Greek word kyanos for "dark blue." It is sometimes called "sappare." The color is not always uniform; it can be blotchy or streaky. The crystals are transparent to translucent, and are found in long blades or columns. Kyanite forms during regional metamorphism under elevated temperatures and pressures, in rocks such as gneiss and schist. While most minerals have just one hardness, kyanite has a range of 4.5-6.5; the hardness varies depending on which way the stone is scratched (because kyanite's crystals are so long and thin). Kyanite is seldom faceted due to difficulties in cutting, and remains an unusual collector's gem.
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