Yellow crystal aggregates of the very rare mineral Al-vanadate mineral steigerite associated to dark red metahewettite from the famous Cactus Rat mine in Utah (Cactus Rat Mine, The Poison Strip, Grand County, Utah, United States of America). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Steigerite
Steigerite is an IMA-recognized mineral species in the vanadate class, with the chemical formula Al(VO₄)·3H₂O.
Key properties: Mohs hardness 2.5–3; specific gravity 2.52–2.58; Waxy in compact aggregates luster; optically biaxial.
IMA symbol Sgr, grandfathered status — known before the IMA’s founding, named in 1935.
Found in U–V deposits impregnating sandstone (Gypsum Valley, Colorado, USA); a weathering product in vanadium-rich schists (Kara-Tau Mountains, Kazakhstan).
It is found associated with Fervanite, corvusite, gypsum (Gypsum Valley, Colorado, USA); navajoite, tyuyamunite, rauvite, hewettite (Monument No. 2 mine, Arizona, USA); vanalite.
The mineral was named to honor Dr. George Steiger (1869–1944), Chief Chemist, U.S. Geological Survey, Washington, D.C., USA.