Mineral Information and Data:

MgSO4 • 7H2O [CNMNC approved formula]

Named for the occurrence at Epsom, England. The mineral was previously known, but was named epsonite only in 1806.

IMA status : Valid species (Pre-IMA 1806) Grandfathered
(8th edition) :  
  (29) Hydrated Acid and Sulfates
  (29.06) where A XO4 · x(H2O)
  (29.06.11) Epsomite Group
(10th edition) :
  (07) Sulfates (selenates, tellurates, chromates, molybdates, wolframates)
  (07.C) Sulfates (selenates, etc.) without Additional Anions, with H2O
  (07.CB) With only medium-sized cations
Crystal system: Orthorhombic System
Point group (H-M): 222 — disphenoidal
Space group: P212121
Unit cell: a = 11.876(2)Å, b = 12.002(2)Å, c =6.859(1)Å, Z=4
Crystal Habit: Rare as crystals, prismatic along {110}, to 8cm; typically as fibrous crusts, woolly efflorescences, botryoidal to reniform masses, stalactitic.
Twinning: Rare on {110}
Color: Colorless to white, pale pink, pale green; colorless in transmitted light
Diaphaneity: Transparent to translucent
Luster: Vitreous, silky in fibrous aggregates
Hardness (Mohs): 2 - 2.5
Measured Density: 1.677(2) g/cm3
Cleavage: {010}, perfect; {101}, distinct
Fracture: Conchoidal
Polymorphism and Series: Forms two series, with goslarite and with morenosite.
Geologic Setting: As efflorescences on the walls of mines, caves, and outcrops of sulfide-bearing magnesian rocks; a product of evaporation at mineral springs and saline lakes; a hydration product of kieserite and langbeinite; rarely a fumarolic sublimate.
Mineral Association: Melanterite, gypsum, halotrichite, pickeringite, alunogen, rozenite (efflorescences); mirabilite (lacustrine evaporites)
Other Properties: H2O Soluble.
Comments: Dehydrates readily in dry air; with a bitter taste.


Origin: Schöller mine, Libusin, Kladno, Czech Republic
Sample size: 2 x 4 cm
Photo: Diederik Visser