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  2. Charoite - Wikipedia

    en.wikipedia.org/wiki/Charoite

    Charoite (/ tʃæroÊŠ.aɪt / CHAR-ow-ait) is a rare silicate mineral with the chemical composition K (Ca,Na)2Si4O10(OH,F)•H2O, first described in 1978. It is named after the Chara River, despite its being 70 kilometres (43 mi) away from the discovery place. [ 6 ][ 3 ] When it was discovered, it was thought to be a fake, dyed purple to give it ...

  3. Agate - Wikipedia

    en.wikipedia.org/wiki/Agate

    Agate (/ ˈ æ É¡ ɪ t / AG-it) is a banded 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 ...

  4. Amethyst - Wikipedia

    en.wikipedia.org/wiki/Amethyst

    Amethyst is a purple variety of quartz (SiO. 2) and owes its violet color to irradiation, impurities of iron (Fe3+. ) and in some cases other transition metals, and the presence of other trace elements, which result in complex crystal lattice substitutions. [2][3][4] The irradiation causes the iron Fe3+.

  5. Gold coin - Wikipedia

    en.wikipedia.org/wiki/Gold_coin

    Gold coins for sale at the Dubai Gold Souk. A gold coin is a coin that is made mostly or entirely of gold. Most gold coins minted since 1800 are 90–92% gold (22‑ karat), while most of today's gold bullion coins are pure gold, such as the Britannia, Canadian Maple Leaf, and American Buffalo. Alloyed gold coins, like the American Gold Eagle ...

  6. Coinage metals - Wikipedia

    en.wikipedia.org/wiki/Coinage_metals

    The coinage metals comprise those metallic chemical elements and alloys which have been used to mint coins. Historically, most coinage metals are from the three nonradioactive members of group 11 of the periodic table: copper, silver and gold. Copper is usually augmented with tin or other metals to form bronze.

  7. Precious metal - Wikipedia

    en.wikipedia.org/wiki/Precious_metal

    The best known precious metals are the coinage metals, which are gold and silver. Although both have industrial uses, they are better known for their uses in art, jewelry, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely ...

  8. List of U.S. state minerals, rocks, stones and gemstones

    en.wikipedia.org/wiki/List_of_U.S._state...

    In 1965, California became the first state to name an official state rock. A 2010 effort led by State Senator Gloria J. Romero, a Democrat from Los Angeles, sought to remove serpentine from its perch as the state's official stone.

  9. Electrum - Wikipedia

    en.wikipedia.org/wiki/Electrum

    The name is mostly applied informally to compositions between 20–80% gold and 80–20% silver, but these are strictly called gold or silver depending on the dominant element. Analysis of the composition of electrum in ancient Greek coinage dating from about 600 BC shows that the gold content was about 55.5% in the coinage issued by Phocaea .

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