“Epsomite” has been identified on Europa, a moon of Jupiter. Phil Plait:
[Astronomers] Brown and Hand, using the monster 10-meter Keck telescope, discovered the presence of magnesium sulfate—MgSO4, a mineral called epsomite—on Europa’s trailing hemisphere (but not the leading half). This has never been seen before, even by probes sent to look at the moon.
This also contributes to the case that Europa has a large ocean lurking under its icy surface, which could be hospitable for life.
Europa — one of the coolest moons in the solar system. Get your Epsom salts here! Step right up!
Epsomite is the mineral form of Epsom salts, which naturally occur mainly in encrustations and effloresences (coatings on porous rock). But the rare crystalline form is fibrous and looks like fur! And there’s also a rare acicular form — spikey! In my imagination, all the epsomite on Europa is fibrous and acicular.
Encrusted epsomite (mineral magnesium sulfate), its most common form.
More exotic fibrous epsomite.
Acicular (spikey) epsomite, very teensy. This view is under a millimetre wide.