Mathesiusite

Mathesiusite is a sulfate mineral containing potassium, vanadium, and uranium and has the chemical formula: K₅(UO₂)₄(SO₄)₄(VO₅)·4(H₂O). It is a secondary mineral formed during post-mining processes.

Mathesiusite
Yellow microcrystals of the extremely rare uranium mineral mathesiusite (IMA 2013-046) from one of the only two known localities worldwide: North Mesa Mine group, Temple Mountain, Emery County, Utah, United States of America.
General
Category	Sulfate mineral
Formula	K5(UO2)4(SO4)4(VO5)·4(H2O)
IMA symbol	Mhe[1]
Strunz classification	7.DG.
Crystal system	Tetragonal
Crystal class	P4/n
Identification
Color	Yellowish green
Crystal habit	Needles <0.2 mm in length
Cleavage	Perfect {010}, good {001}
Fracture	Irregular/uneven
Tenacity	Brittle
Mohs scale hardness	2
Streak	Greenish white
Specific gravity	4.02 (calculated)
Optical properties	Uniaxial (−)
Refractive index	nω = 1.634() nε = 1.597(3)
Birefringence	δ = 0.037
Other characteristics	Radioactive
References	[2][3]

It was discovered in the Jáchymov mining district, Czech Republic and named in 2013 after Johannes Mathesius (1504–1565), who studied minerals from the area (known then as Joachimsthal, Bohemia).^[4]