Meridianiite
Magnesium sulfate undecahydrate — a salt stable only below ~2 °C, named for Meridiani Planum on Mars where it may exist.
Intro adapted from Wikipedia (CC BY-SA).
Meridianiite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Mg(SO₄)·11H₂O.
Key properties: specific gravity 1.507.
IMA symbol Mdn, IMA status: approved, named in 2007.
Found in a pocket near the surface of a frozen pond that allowed evaporation, concentration of dissolved matter, and crystallization at temperatures well below the freezing point of water. In sea ice inclusions and Antarctic ice.
It is found associated with Ice.
The name is derived from the locality where the Mars Exploration Rover (MER) Opportunity observed crystal molds in sedimentary rock that may be caused by minerals that have since dehydrated or dissolv.