Orange red sharp crystals of maxwellite, a very rare mineral only found in two localities worldwide in a white contrasting matrix. From: Squaw Creek Mine, Sierra County, New Mexico, United States of America. — Photo: David Hospital · CC BY-SA 4.0
Maxwellite
Maxwellite is an IMA-recognized mineral species in the arsenate class, with the chemical formula NaFe³⁺(AsO₄)F.
It crystallizes in the monoclinic crystal system (space group C2/c). It is a member of the Titanite structural group.
Key properties: Mohs hardness 5–5.5; specific gravity 3.9; Medium to pale red-orange streak; Vitreous luster; optically biaxial.
IMA symbol Max, IMA status: approved, named in 1987.
Rarely formed in miarolitic cavities in rhyolite adjacent to high-temperature veins in hydrothermal tin deposits.
It is found associated with Squawcreekite, cassiterite, hematite, quartz, tridymite, pseudobrookite, sanidine, chernovite-(Y), gasparite-(Ce), tilasite, heulandite, stilbite, calcite.
The mineral was named to honor Charles Henry Maxwell (1923–), geologist with the U.S. Geological Survey, who studied the Taylor Creek district.