Search results
Results from the WOW.Com Content Network
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.
There are over 300 types of minerals that have been used as gemstones. Such as: A–B ... Opal. Fire opal; Moss opal; Painite; ... Tourmaline subgroup: Achroite (var ...
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.
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]
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 ...
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.
The "chelsea" filter was originally devised by Anderson and Payne in 1934 of the Gem testing Laboratory of the London Chamber of Commerce & Industry.The filter was devised with the collaboration of gemmology students of the Chelsea College of Science and Technology where Basil Anderson was an instructor for the Gemmological Association of Great Britain.
Unpolished sunstone. The optical effect is due to reflections from inclusions of red copper, hematite, or goethite, in the form of minute scales, which are hexagonal, rhombic, or irregular in shape, and are disposed parallel to the principal cleavage-plane.