Meridianiite

Meridianiite
Meridianiite crystals displaying blocky, triclinic, crystal forms.
General
Category	Sulfate minerals
Formula (repeating unit)	Magnesium sulfate 11 hydrate MgSO4·11H2O
IMA symbol	Mdn[1]
Strunz classification	7.CB.90
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 6.7459 Å b = 6.8173 Å c = 17.299 Å; α = 88.137°, β = 89.481°, γ = 62.719° Z = 2
Identification
Formula mass	318.55 g/mol
Color	Colorless or white
Crystal habit	Needle-shaped to broad flat crystals
Tenacity	Brittle
Luster	Vitreous – dull
Streak	White
Diaphaneity	Transparent
Specific gravity	1.512
Melting point	At temperatures above 2 °C
Solubility	Highly soluble in water
References	[2][3]

Meridianiite is the mineral consisting of magnesium sulfate undecahydrate, MgSO
₄·11H
₂O. It is colorless transparent crystalline salt that precipitates from solutions saturated in Mg²⁺ and SO₄²⁻ ions at temperatures less than 2 °C.^[4] The synthetic compound was formerly known as Fritzsche's salt.^[4][5]

Meridianiite is a naturally occurring mineral species found on Earth in a variety of environments including sea ice, crusts and efflorescences in coal/metal mines, cave systems, oxidized zones of sulfide deposits, salt lakes/playas and Antarctic ice-cores.^[6][4] It is commonly associated with other evaporite minerals such as epsomite, mirabilite, halides, and other sodium-magnesium-sulfates. There is some evidence that it was once present on the surface of Mars, and may occur in several bodies of the Solar System.^[4] As of 2012, it was the only undecahydrate sulfate known.^[7]