Editing Topaz (section)

==Characteristics==
[[File:Topaz-k-182a.jpg|thumb|upright=0.75|Blue topaz crystal]]
Topaz in its natural state is colorless, often with a greyish cast. It also occurs as a golden brown to yellow color which makes it sometimes confused with [[citrine quartz|citrine]], a less valuable gemstone.<ref name="HurrellJohnson2016">{{cite book |first1=Karen |last1=Hurrell |first2=Mary L. |last2=Johnson |title=Gemstones: A Complete Color Reference for Precious and Semiprecious Stones of the World |url=https://books.google.com/books?id=KLSTDgAAQBAJ&pg=PA169 |date=15 December 2016 |publisher=Book Sales |isbn=978-0-7858-3498-4 |page=169}}</ref> The [[specific gravity]] of all shades of topaz, however, means that it is considerably heavier than citrine (about 25% per volume) and this difference in weight can be used to distinguish two stones of equal volume. Also, if the volume of a given stone can be determined, its weight if it were topaz can be established and then checked with a sensitive scale. Likewise, glass stones are also much lighter than equally sized topaz.

A variety of impurities and treatments may make topaz wine red, pale gray, reddish-orange, pale green, or pink (rare), and opaque to translucent/transparent. The pink and red varieties come from chromium replacing aluminium in its crystalline structure.<ref>{{Cite journal |last=Gübelin |first=Edward |last2=Graziani |first2=Giorgio |last3=Kazmi |first3=A. H. |date=1986-10-01 |title=Pink Topaz from Pakistan |url=http://www.gia.edu/gems-gemology/fall-1986-pink-topaz-g%EF%BF%BDbelin |journal=Gems & Gemology |volume=22 |issue=3 |pages=140–151 |doi=10.5741/GEMS.22.3.140 |issn=0016-626X|url-access=subscription }}</ref>
[[File:Topaz with irradiated fragment - Smithsonian Museum of Natural History - 2012-05-17.jpg|thumb|Large topaz gemstone and small irradiated topaz fragment on display at the Smithsonian Museum of Natural History.]]
Imperial topaz is yellow, pink (rare, if natural), or pink-orange. Brazilian imperial topaz can often have a bright yellow to deep golden brown hue, sometimes even violet. Many brown or pale topazes are treated to make them bright yellow, gold, pink, or violet colored. Some imperial topaz stones can fade from exposure to sunlight for an extended period of time.<ref>{{cite web |url=http://www.nhm.org/research/minsci/impgem.htm |title=Imperial topaz |archive-url=https://web.archive.org/web/20090513005018/http://www.nhm.org/research/minsci/impgem.htm |archive-date=2009-05-13 |df=dmy-all |publisher=[[Natural History Museum of Los Angeles County]] |website=nhm.org}}</ref><ref name="Emporia">{{cite web |url=http://academic.emporia.edu/abersusa/go340/topaz.htm |title=Gemstones & Gemology – Topaz |publisher=[[Emporia State University]] |website=academic.emporia.edu}}</ref> Naturally occurring blue topaz is quite rare. Typically, colorless, gray, or pale yellow and blue material is heat treated and [[Gemstone irradiation|irradiated]] to produce a more desired darker blue.<ref name="Emporia" /> Mystic topaz is a colorless topaz that has been artificially coated via a [[vapor deposition]] process giving it a rainbow effect on its surface.<ref>{{cite web |url=http://www.farlang.com/art/mystic-topaz |title=Mystic topaz, consumer information |website=Farlang.com |date=2008-10-30 |access-date=2011-10-29 |df=dmy-all}}</ref>[[File:Topaz-k312b.jpg|thumb|upright=0.75|left|Sherry-colored topaz from Utah, USA]]

Although very hard, topaz must be treated with greater care than some other minerals of similar hardness (such as [[corundum]]) because of a weakness of atomic bonding of the stone's molecules along one or another axial plane (whereas diamonds, for example, are composed of carbon atoms bonded to each other with equal strength along all of its planes). This gives topaz a tendency to break along such a cleavage plane if struck with sufficient force.<ref name="Newman2015">{{cite book |first=Renee |last=Newman |title=Gem & Jewelry Pocket Guide: A traveler's guide to buying diamonds, colored gems, pearls, gold and platinum jewelry |url=https://books.google.com/books?id=wK5UDQAAQBAJ&pg=PT104 |date=7 January 2015 |publisher=BookBaby |isbn=978-0-929975-49-8 |page=104}}</ref>

Topaz has a relatively low [[index of refraction]] for a gemstone, and so stones with large facets or tables do not sparkle as readily as stones cut from minerals with higher refractive indices, though quality colorless topaz sparkles and shows more "life" than similarly cut quartz. When given a typical "brilliant" cut, topaz may either show a sparkling table facet surrounded by dead-looking crown facets or a ring of sparkling crown facets with a dull well-like table.<ref name="Dake,2013">{{cite book |author=Dake, H. |title=The Art of Gem Cutting – including cabochons, faceting, Sspheres, tumbling, and special techniques |url=https://books.google.com/books?id=ybB8CgAAQBAJ&pg=PT105 |date=16 April 2013 |publisher=Read Books Limited |isbn=978-1-4474-8480-6 |page=105}}</ref>  It also takes an exceptionally fine polish, and can sometimes be distinguished from citrine by its slippery feel alone (quartz cannot be polished to this level of smoothness).<ref name=ref1>{{cite book|title=Gem Testing|author=B. Anderson|date=2011|publisher=Read Books}}</ref>

Another method of distinguishing topaz from quartz is by placing the unset stone in a solution of [[bromoform]] or [[methylene iodide]].  Quartz will invariably float in these solutions, whereas topaz will sink.<ref name=ref1/>