Crystal is one of the narrow gemstones and is a very old gem. Its chemical composition is silica. This is a crystal that is transparent like water in quartzite minerals (although crystals are opaque, they can only be called quartz crystals). If it is purple, brown or black due to impurities, it is called amethyst, sapphire and smoky crystal; special varieties containing acicular or fibrous mineral inclusions inside.
Called "hair crystal". The crystal face is glassy, its shell-like fracture is grease-like; the hardness is 7. The specific gravity is 2.66, and it has a pressure-sensitive and optical property. Water crystals are widely used. They are mainly used as bracelets and necklace beads in jewelry. They also make small pendants and ornaments. Crystals are mainly produced in Brazil and Uruguay. The main producing areas in China are Yangjiaoling in Hainan Province and the East China Sea in Jiangsu Province. Natural crystals are clear and transparent, often containing gas-liquid inclusions of star-like, cloud-like or floc-like spreads, and often exhibit microcracks. Synthetic crystals have no cracks, but often have small bubbles. In addition, the amount of synthetic crystal can be felt by hand to be larger than that of natural crystal. Compared with glass, the crystal is white and bright and dazzling. The glass white is slightly blue, yellow and bright. The crystal hardness is 7, the glass is 5.5, the crystal can be used to cut the glass, the natural crystal often contains uneven cotton, etc. Phenomenon, and the glass is artificially baked, often uniform without cotton, and has tiny bubbles. The tongue crystal has a cool feeling, and the glass has a warm feeling.