Editing Spinel (section)

==Properties==
[[File:Spinelgem.JPG|thumb|left|Cut spinel]]
Spinel crystallizes in the isometric system; common crystal forms are [[octahedron|octahedra]], usually [[Crystal twinning|twinned]]. It has no true [[Cleavage (crystal)|cleavage]], but shows an octahedral [[Parting (crystal)|parting]] and a [[conchoidal fracture]].<ref>{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=362–363}}</ref> Its [[Mohs scale of mineral hardness|hardness]] is 8, its [[specific gravity]] is 3.5–4.1, and it is transparent to opaque with a vitreous to dull [[Lustre (mineralogy)|luster]]. It may be colorless, but is usually various shades of red, [[lavender (color)|lavender]], blue, green, brown, black, or yellow.<ref name="klein-hurlbut">{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st}}</ref> Chromium(III) causes the red color in spinel from Burma.<ref>{{Cite web |title=Minerals Colored by Metal Ions |url=http://minerals.gps.caltech.edu/color_causes/Metal_Ion/index.html |access-date=2023-03-01 |website=minerals.gps.caltech.edu}}</ref> Some spinels are among the most famous gemstones; among them are the [[Black Prince's Ruby]] and the "[[Timur ruby]]" in the British [[Crown Jewels of the United Kingdom|Crown Jewels]],<ref name="Butler1989">{{cite book|author=Sir Thomas Butler|title=The Crown Jewels and Coronation Ceremony|url=https://books.google.com/books?id=brbvmKAQ5PEC|year=1989|publisher=Pitkin|isbn=978-0-85372-467-4|page=6}}</ref> and the "Côte de Bretagne", formerly from the French Crown jewels.<ref>{{cite journal |last1=Pardieu |first1=V. |last2=Farkhodova |first2=T. |title=Spinel from Tajikistan |journal=InColor |date=Summer 2019 |pages=30–33 |url=https://www.researchgate.net/publication/339439345 |accessdate=28 April 2021}}</ref> The [[Samarian Spinel]] is the largest known spinel in the world, weighing {{convert|500|carat|g}}.<ref>{{cite journal |title=Samarian spinel |journal=Dictionary of Gems and Gemology |date=2005 |pages=657–737 |doi=10.1007/3-540-27269-0_19}}</ref>

The transparent red spinels were called spinel-rubies<ref>{{cite journal |last1=Lytvynov |first1=L.A. |year=2011 |title=On the words used as names for ruby and sapphire |journal=Functional Materials |volume=18 |number=2 |page=275 |url=http://dspace.nbuv.gov.ua/bitstream/handle/123456789/135445/21-Lytvynov.pdf?sequence=1 |accessdate=29 April 2021}}</ref> or balas rubies.<ref>{{cite journal |last1=Hughes |first1=R.W. |year=1994 |title=The rubies and spinels of Afghanistan: A brief history |journal=Journal of Gemmology |volume=24 |number=4 |pages=256–267 |doi=10.15506/JoG.1994.24.4.256 |url=https://gem-a.com/images/Documents/JoG/Archive/1956-97/JoG1994_24_4.pdf#page=26 |accessdate=29 April 2021}}</ref> In the past, before the arrival of modern science, spinels and rubies were equally known as rubies. After the 18th century, the word ruby was only used for the red gem variety of the mineral [[corundum]], and the word spinel came to be used.{{sfn|Pardieu|Farkhodova|2019}} "Balas" is derived from Balascia, the ancient name for [[Badakhshan]], a region in central [[Asia]] situated in the upper valley of the [[Panj River]], one of the principal tributaries of the [[Oxus River]]. However, "Balascia" itself may be derived from [[Sanskrit]] ''bālasūryaka'', which translates as "crimson-coloured morning sun".<ref>{{cite book |last1=Biswas |first1=A.K. |editor1-last=Ramachandra Rao |editor1-first=P. |editor2-last=Goswami |editor2-first=N.G. |title=Metallurgy in India : a retrospective |date=2001 |publisher=India International Publisher |location=New Delhi |asin=B002A9M6QU |pages=1–22 |chapter=Minerals and their Exploitation in Ancient and Pre-modern India}}</ref> Mines in the [[Gorno Badakhshan]] region of [[Tajikistan]] constituted for centuries the main source for red and pink spinels.{{sfn|Pardieu|Farkhodova|2019}}