Epsomite is a highly soluble hydrated magnesium sulfate mineral that typically forms as delicate, needle-like crystals or white crusts. It is most commonly found as efflorescence in caves, mine tunnels, or near volcanic vents where water evaporates quickly. Due to its extreme solubility, specimens must be stored in airtight containers to prevent dehydration and crumbling.
Is this epsomite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch epsomite with a known reference. Epsomite sits at Mohs 2-2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Epsomite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Epsomite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, pink, yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, fibrous, botryoidal, or as efflorescent crusts.
Often confused with
Epsomite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside epsomite
Minerals reported to co-occur with epsomite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgSO₄·7H₂O
- Mohs hardness
- 2-2.5
- Density
- 1.67 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, Fibrous, Botryoidal, Or as Efflorescent Crusts
- Cleavage
- Perfect in One Direction
- Rarity
- Common
- Uses
- Collector, Industrial, Bath Salts
- Host rock
- Evaporite Deposits, Volcanic Fumaroles, And Mine Walls
- Typical price
- $5-30 for small mineral specimens
Where rockhounds find epsomite
2 mapped spotsClassic worldwide localities
- Epsom, Surrey, England
- Mount St. Helens, USA
- Kalgoorlie, Australia
- Chile
- Germany
Field-hunting tip
Look in evaporite deposits, volcanic fumaroles, and mine walls country — that is the host setting where epsomite typically forms. If you start seeing gypsum, halite, mirabilite in float, you are in the right ground. Field specimens usually show a acicular, fibrous, botryoidal, or as efflorescent crusts habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Mexico, Utah — start trip planning there.
Common questions
How do you identify epsomite?+
Where is epsomite found?+
Can I find epsomite in the United States?+
How much is epsomite worth?+
What rocks look like epsomite?+
What minerals are found with epsomite?+
What kind of rock does epsomite form in?+
What is epsomite used for?+
Find epsomite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
