| Melanterite | |
| Category: | Sulfate mineral |
| Formula: | FeSO4·7H2O |
| Imasymbol: | Mln[1] |
| Strunz: | 7.CB.35 |
| Dana: | 29.06.10.01 |
| System: | Monoclinic |
| Class: | Prismatic (2/m) (same H-M symbol) |
| Symmetry: | P21/c |
| Unit Cell: | a = 14.077 Å, b = 6.509 Å, c = 11.054 Å; β = 105.6°; Z = 4 |
| Color: | Green, pale green, greenish blue, bluish green, colorless |
| Habit: | Encrustations and capillary efflorescences; rarely as equant pseudo-octahedral, prismatic or tabular crystals |
| Cleavage: | Perfect, Distinct |
| Fracture: | Conchoidal |
| Mohs: | 2 |
| Luster: | Vitreous |
| Streak: | White |
| Diaphaneity: | Subtransparent to translucent |
| Gravity: | 1.89 – 1.9 |
| Opticalprop: | Biaxial (+) |
| Refractive: | nα = 1.470 – 1.471 nβ = 1.477 – 1.480 nγ = 1.486 |
| References: | [2] [3] [4] [5] |
Melanterite is a mineral form of hydrous iron(II) sulfate: FeSO4·7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by loss of water. It is a secondary sulfate mineral which forms from the oxidation of primary sulfide minerals such as pyrite and marcasite in the near-surface environment. It often occurs as a post mine encrustation on old underground mine surfaces. It also occurs in coal and lignite seams exposed to humid air[3] and as a rare sublimate phase around volcanic fumaroles.[5] Associated minerals include pisanite, chalcanthite, epsomite, pickeringite, halotrichite and other sulfate minerals.[5]
It was first described in 1850.[5]