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2. List of gemstones by species - Wikipedia

   en.wikipedia.org/wiki/List_of_gemstones_by_species

   Rock crystal (var.) Shocked quartz (var.) Smoky quartz (var.) Quartzite; R–Z ... Some minerals made into gemstones may display a chatoyancy or cat's eye effect, ...

3. List of minerals - Wikipedia

   en.wikipedia.org/wiki/List_of_minerals

   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.

4. Gemstone - Wikipedia

   en.wikipedia.org/wiki/Gemstone

   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 ...

5. Agate - Wikipedia

   en.wikipedia.org/wiki/Agate

   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 ...

6. Gemology - Wikipedia

   en.wikipedia.org/wiki/Gemology

   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.

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

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

   Leaders of states in the U.S. which have significant mineral deposits often create a state mineral, rock, stone or gemstone to promote interest in their natural resources, history, tourism, etc. Not every state has an official state mineral, rock, stone and/or gemstone, however.