Wiktionary
geigerite
n. (context mineral English) A triclinic-pinacoidal mineral containing arsenic, hydrogen, manganese, and oxygen.
Wikipedia
Geigerite
Geigerite is a mineral, a complex hydrous manganese arsenate with formula: Mn(AsOOH)(AsO)·10HO. It forms triclinic pinacoidal, vitreous, colorless to red to brown crystals. It has a Mohs hardness of 3 and a specific gravity of 3.05.
It was discovered in Grischun, Switzerland in 1989. It was named in honor of Thomas Geiger (1886–1976), Wiesendangen, Switzerland, who studied the Falotta manganese ores.