Editing Tourmaline (section)

=== Color ===
[[File:Three tourmalines flash III.jpg|thumb|Two dark-green rectangular tourmaline stones and one oval tourmaline stone]]
[[File:tourmaline.xtal.750pix.jpg|thumb|upright|Bi-chromatic tourmaline crystal, {{convert|0.8|in|cm|0}} long]]
[[File:Tourmaline Mineral Macro 2.JPG|thumb|Tourmaline mineral, approximately {{cvt|10|cm}} tall]]

Tourmaline has a variety of colors. Iron-rich tourmalines are usually black to bluish-black to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are almost any color: blue, green, red, yellow, pink, etc. Rarely, it is colorless. Bi-colored and multicolored crystals are common, reflecting variations of fluid chemistry during crystallization. Crystals may be green at one end and pink at the other, or green on the outside and pink inside; this type is called {{visanc|Watermelon tourmaline|text=[[watermelon]] tourmaline}} and is prized in jewelry.  An excellent example of watermelon tourmaline jewelry is a brooch piece (1969, gold, watermelon tourmaline, diamonds) by [[Andrew Grima]] (British, b. Italy, 1921–2007), in the collection of Kimberly Klosterman and on display at the [[Cincinnati Art Museum]].<ref>{{Cite web|date=2022-01-19|title=Simply Brilliant – An Exceptional Collection of Fine Jewelry with Outstanding Stones and Crystals {{!}} GeoRarities|url=https://georarities.com/2022/01/19/simply-brilliant-an-exceptional-collection-of-fine-jewelry-with-outstanding-stones-and-crystals/|access-date=2022-01-27|language=en-US}}</ref> Some forms of tourmaline are [[Dichroism|dichroic]]; they change color when viewed from different directions.<ref>{{Cite web|title=Tourmaline {{!}} mineral|url=https://www.britannica.com/science/tourmaline-mineral|access-date=2021-06-03|website=Encyclopedia Britannica|language=en}}</ref>

The pink color of tourmalines from many localities is the result of prolonged natural irradiation. During their growth, these tourmaline crystals incorporated [[Manganese|Mn<sup>2+</sup>]] and were initially very pale. Due to natural [[gamma ray]] exposure from [[radioactive decay]] of [[Potassium-40|<sup>40</sup>K]] in their [[granitic]] environment, gradual formation of Mn<sup>3+</sup> ions occurs, which is responsible for the deepening of the pink to red color.<ref name="Reinitz & Rossman 1988">Reinitz & Rossman, 1988.</ref>