Black metallic crystal aggregates of the extremely rare Hemlo mineral Tomichite from one of the only two known localities worldwide and associated to golden pyrite (Hemlo Gold Deposit, Hemlo, Thunder Bay District, Ontario, Canada). Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Tomichite
Tomichite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula V³⁺₄Ti⁴⁺₃As³⁺O₁₃(OH).
It crystallizes in the monoclinic crystal system (space group A2/m).
Key properties: Mohs hardness 6; specific gravity 4.16; Black streak.
IMA symbol Tom, IMA status: approved, named in 1978.
Found in a specimen from a hydrothermal gold deposit (Kalgoorlie, Western Australia); in a gold deposit at the contact of felsic metavolcanic and metasedimentary rocks (Hemlo deposit, Canada).
It is found associated with Vanadian muscovite, rutile, pyrite, calaverite, calcite, quartz (Kalgoorlie, Western Australia); quartz, microcline, barite, pyrite, molybdenite, stibnite.
The mineral was named to honor Stephan A. Tomich (1914–), consulting geologist, Perth, Western Australia, who presented the first specimen for examination.