Editing Ullmannite (section)

==Physical properties==
Ullmannite is steel-gray to tin white in color with a metallic luster, has a [[Mohs hardness]] of 5 to 5.5 and a [[specific gravity]] of 6.65. Initially thought to be of two species, tetrahedral and cubic, it was later confirmed that both samples conformed to the 23 point group of the [[cubic (crystal system)|isometric crystal class]] and typically exhibits cubic, octahedral, or pyritohedral forms although euhedral crystals are rare.<ref name="Miers-1891">{{cite journal
|last=Miers
|first=A.H.
|year=1891
|title=The Tetardohedrism of Ullmannite. 
|journal=Mineralogical Magazine
|volume=9
|issue=43
|pages=211–213
|doi=10.1180/minmag.1891.009.43.03|bibcode=1891MinM....9..211M
}}</ref>

Variance in its chemical composition has been shown to be responsible for loss of symmetry and variations in striation patterns.<ref name="Takeuchi-1957">{{cite journal
|last=Takeuchi
|first=Y.
|year=1957
|title=The Absolute Structure of Ullmannite, NiSbS.
|journal=Mineralogical Journal
|volume=2
|issue=2
|pages=90–102
|url=http://www.journalarchive.jst.go.jp/english/jnlabstract_en.php?cdjournal=minerj1953&cdvol=2&noissue=2&startpage=90
|doi=10.2465/minerj1953.2.90
|bibcode=1957MinJ....2...90T
|doi-access=free
}}{{Dead link|date=May 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Ullmannite crystals are usually less than 2&nbsp;mm, however larger have been identified in especially antimony rich environments.<ref name="Zhu-2010">{{cite journal
|last=Zhu
|first=Y.
|author2=An, F.
 |year=2010
|title=Native Antimony in the Baogutu gold deposit( West Junggar, NW China): Its occurrence and origin
|journal=Ore Geology Reviews
|volume=37
|issue=3–4
|pages=214–223
 |doi=10.1016/j.oregeorev.2010.03.005|bibcode=2010OGRv...37..214A
}}</ref>  Ullmannite commonly displays interpenetration twins as well as enantiomorphic twinning along [110].<ref name=HBM/>