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Rock crystal (var.) Shocked quartz ... Some rocks are used as gems, including: Anthracite; ... Some minerals made into gemstones may display a chatoyancy or cat's eye ...
Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster. A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is ...
Differences in chemical composition and crystal structure distinguish the various species. Within a mineral species there may be variation in physical properties or minor amounts of impurities that are recognized by mineralogists or wider society as a mineral variety. Mineral variety names are listed after the valid minerals for each letter.
Gemstones are basically categorized based on their crystal structure, specific gravity, refractive index, and other optical properties, such as pleochroism. The physical property of "hardness" is defined by the irregular Mohs scale of mineral hardness. Gemologists study these factors while valuing or appraising cut and polished gemstones.
Agate (/ ˈ æ ɡ ɪ t / AG-it) is a variety of chalcedony, [1] which comes in a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks.The ornamental use of agate was common in ancient Greece, in assorted jewelry and in the seal stones of Greek warriors, [2] while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus ...
For example, the Greek word asbestos (meaning 'inextinguishable', or 'unquenchable'), for the unusual mineral known today containing fibrous structure. [5] The ancient historians Strabo (63 BC–19 AD) and Pliny the Elder (23–79 AD) both wrote of asbestos, its qualities, and its origins, with the Hellenistic belief that it was of a type of ...
Bahia Emerald [2]; Carolina Emperor, [3] [4] 310 carats uncut, 64.8 carats cut; discovered in the United States in 2009, resides in the North Carolina Museum of Natural Sciences, Raleigh, NC, US
Navaratna (nine gems) is a powerful jewel frequently worn by a Maharaja (Emperor). It is an amulet, which comprises diamond, pearl, ruby, sapphire, emerald, topaz, cat's eye, coral, and hyacinth (red zircon). Each of these stones is associated with a celestial deity, representing the totality of the Hindu universe when all nine gems are together.