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Each of the three notable types of opal – precious, common, and fire [3] – display different optical effects; therefore, the intended meaning varies depending on context. The general definition of opalescence is a milky iridescence displayed by an opal, which describes the visual effect of precious opal very well, and opalescence is ...
Upload file; Search. Search. Appearance. Donate; ... There are over 300 types of minerals that have been used as gemstones. Such as: ... Tourmaline subgroup: Achroite ...
Elbaite is allochromatic, meaning trace amounts of impurities can tint crystals, and it can be strongly pleochroic. Every color of the rainbow may be represented by elbaite, some exhibiting multicolor zonation. Microscopic acicular inclusions in some elbaite crystals show the cat's eye effect in polished cabochons.
Today this tourmaline locality (type locality for dravite) at Dobrova (near Dravograd), is a part of the Republic of Slovenia. [9] Tschermak gave this tourmaline the name dravite, for the Drava river area, which is the district along the Drava River (in German: Drau, in Latin: Drave) in Austria and Slovenia.
In 1912, to standardize birthstones, the (American) National Association of Jewelers (now called Jewelers of America) met in Kansas and officially adopted a list. [1]: 317 The Jewelry Industry Council of America updated the list in 1952 [3]: 311 by adding Alexandrite for June, citrine for November and pink tourmaline for October.
Pleochroism of cordierite shown by rotating a polarizing filter on the lens of the camera Pleochroism of tourmaline shown by rotating a polarizing filter on the lens of the camera. Pleochroism is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. [1]
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Rubellite used to be the most expensive and prized gem in the tourmaline group but has since been eclipsed by the Paraiba tourmaline. [7] [8] The most valuable specimens are colored red and lack brown. [3] Those that are of ruby color are the most valuable. [9]