THE MINERAL KIESERITE

Chemistry: MgSO₄ - H₂O, Hydrated Magnesium Sulfate.
Class: Sulfates
Group: Kieserite
Uses: As a minor source of magnesium and as mineral specimens.
Specimens

Kieserite, which is named after D. G. Kieserr, forms in marine evaporite deposits where sea water has been concentrated and exposed to prolonged evaporation. Other marine evaporite minerals include calcite, dolomite, gypsum, anhydrite, halite, polyhalite, kainite, picromerite, carnallite and sylvite, among several others. Evaporite minerals are geologically important because they clearly are related to the environmental conditions that existed at the time of their deposition, namely coastal arid. They also can be easily recrystallized in laboratories in order to postulate their specific characteristics of formation. Specimens of kieserite must be stored in a closed container as they will absorb water from the air and convert to the mineral epsomite, MgSO₄ - 7H₂O. If later the mineral dehydrates, it will form the mineral hexahydrite, MgSO₄ - 6H₂O.

Kieserite lends its name to a group of sulfates called the Kieserite Group. These sulfates are all monoclinic, have medium sized cations and are mono-hydrated (one water molecule). The general formula of this group is ASO₄ - H₂O, where A can be either magnesium, iron, copper, manganese, nickel and/or zinc.
These are the members of the Kieserite Group:

Dwornikite (Hydrated Nickel Iron Sulfate)
Gunningite (Hydrated Zinc Manganese Sulfate)
Kieserite (Hydrated Magnesium Sulfate)
Poitevinite (Hydrated Copper Iron Zinc Sulfate)
Szmikite (Hydrated Manganese Sulfate)
Szomolnokite (Hydrated Iron Sulfate)

THE PHYSICAL CHARACTERISTICS OF KIESERITE:

Color is white, colorless, gray or yellowish.
Luster is vitreous.
Transparency: Crystals are translucent.
Crystal System is monoclinic; 2/m.
Crystal Habits include granular masses. Individual crystals are rare.
Cleavage is perfect in one direction.
Fracture is uneven.
Hardness is 3.5
Specific Gravity is approximately 2.6 (average for translucent minerals).
Streak is white.
Associated Minerals include halite, polyhalite, carnallite, sylvite and other more rare evaporite minerals.
Notable Occurrences include Strassfurt, Saxony, Germany; Poland; Sicily, Italy; Russia; Austria and Carlsbad, New Mexico and Western Texas, USA.
Best Field Indicators are associations, cleavage, habit and environment of formation.