Szomolnokite

Szomolnokite (Fe²⁺SO₄·H₂O) is a monoclinic iron sulfate mineral forming a complete solid solution with magnesium end-member kieserite (MgSO₄·H₂O).^[2] In 1877 szomolnokite's name was derived by Joseph Krenner from its type locality of oxidized sulfide ore containing iron in Szomolnok, Slovakia (Hungary at the time).^[2][3][4]

Szomolnokite
Halotrichite (Hal); szomolnokite (Szo) and voltaite (Vol)
General
Category	Sulfate mineral
Formula	Fe2+SO4 · H2O
IMA symbol	Szo[1]
Strunz classification	7.CB.05
Dana classification	29.6.2.2
Crystal system	Monoclinic
Crystal class	Prismatic (2/m)
Space group	C2/c (no. 15)
Identification
Color	Sulfur-yellow, yellow-brown, red-brown, blue, colorless
Crystal habit	Bipyramidal, distorted, tabular, parallel growths, globular, stalactites
Fracture	Conchoidal to sub-conchoidal, uneven
Tenacity	Brittle
Mohs scale hardness	2.5
Luster	Vitreous
Diaphaneity	Translucent
Specific gravity	3.03–3.07 (measured), 3.10 (calculated)
Optical properties	Biaxial (+), colorless (transmitted light)
2V angle	80° (measured), 86° (calculated)
References	[2][3][4][5]

As of mid-January 2020 the only continent on which szomolnokite has not been found and reported is Antarctica.^[2]

At room temperature szomolnokite is stable up to a pressure of 6.2 GPa, and then transforms into triclinic crystal structure.^[6]