Moldavite (also called Bouteille Stone or vltavin) is a natural glass that is thought to have formed in the heat of an asteroid impact. Moldavite is usually yellowish green, green, or greenish brown in color. It has been cut into faceted and cabochon gemstones. Unlike most gem materials that grow slowly over time in a quiet underground environment, moldavite formed in a burst of heat and energy produced by one of the most violent possible events - the impact of a large hypervelocity object with a planet. The rock in the impact area was instantly vaporized by the heat of the impact, then immediately condensed into a molten liquid, and then almost immediately solidified into an amorphous glass. The condensation and solidification were so fast that mineral crystals did not form, and gases were trapped in the glass.
Most gem-quality moldavite is faceted or cut en cabochon and sold as a collector's gem. Moldavite jewelry should be worn cautiously because it is brittle and has about the same hardness as most man-made glasses (5 to 5.5). Nice pieces of rough moldavite are also used in jewelry. Attractive droplet-shaped pieces are commonly wire-wrapped and made into pendants or earrings. Rough moldavite specimens with representative features are also purchased by meteorite and mineral collectors. The best specimens are often purchased by collectors for a much higher price than what they would have sold for if they were used in jewelry.