Beige crystal aggregates of the very rare mineral esquireite (IMA 2014-066) from the third known locality worldwide, still not uploaded to Mindat: Gun Claim, MacMillan Pass, Yukon, Canada. Associated mineral is white sanbornite. — Photo: David Hospital · CC BY-SA 4.0
Esquireite
Esquireite is an IMA-recognized mineral species in the silicate class, with the chemical formula BaSi₆O₁₃·7H₂O.
It crystallizes in the monoclinic crystal system (space group C2).
Key properties: Mohs hardness 2; specific gravity 2.18; White streak; Vitreous to pearly luster; optically biaxial.
IMA symbol Esq, IMA status: approved, named in 2014.
Formed by low-temperature hydrothermal alteration of sanbornite, during contact metamorphism of Ba-rich sediments.
It is found associated with Cerchiaraite-(Al), kampfite, macdonaldite, pyrrhotite, quartz, titantaramellite, traskite, witherite, opal (Esquire #1 claim); fencooperite, gillespite.
The name refers to the Esquire #1 claim, where the first specimens were collected.