THE MINERAL EPSOMITE: MORE INTERESTING THAT ONE MIGHT THINK

The chemical composition of epsomite is MgSO+7H2O (= hydrous magnesium sulfate). The familiar name of this mineral is “epsom salts,” which can be purchased in small bags at any grocery store or drugstore. This mineral is a medical aid. 

Epsomite occurs in near or near salt-lake environments, on walls of mines (as an efflorescence coating), or in association with stalactites and botryoidal masses in caves. It occurs either as crystals, granular crusts, and fibrous aggregates. This mineral is also present in seawater and is the second most common compound found in it, after sodium chloride.

Also, epsomite may exist in the soils found on the planet Mars. 

Well-formed (i.e., not crowded) crystals, grown under controlled conditions, are clear and have shapes diagnostic of the orthorhombic mineralogical system (e.g., diagnostic type of faceted ends on the ends of the crystals) (see Figure 1 shown below). Commercially available bags (e.g., sold in drugstores) of this mineral, however, contain material derived from fast, raw-mining techniques. These particular crystals are porcelain-like, white, and have been mechanically crushed.  If they show any symmetry at all, it is a simple prismatic (tabular) shape. The hardness of this mineral is 2 to 2.5 (see Figure 2 shown below).

The clear crystals shown below in Figure 3 were grown in situ, by me. I took a small amount (about a tea-spoon) of the commercially available material and dissolved it in a small amount (about 30 ml) of water for a few days. Eventually, the water evaporated, and the resulting crystals came out clear and with mineralogical symmetry. It is best not to put too much material into the water. Then let the solution sit, undisturbed, for a few days. The results (shown below) are astonishing!

Reference Cited:

Berry, L.G. and B. Mason. 1959. Mineralogy concepts, descriptions, determinations. Freeman and Company, San Francisco. 630 pp.

                                                 FIGURES

Figure 1. Sketch of an idealized acicular/rhombic prism crystal of epsomite (based on fig. 251, p. 98, of Berry and Mason (1959). 

Figure 2. Crystals (up to 3.5 mm long) from a drugstore bag of crushed epsomite. If you look carefully, you can see hints of the original faceted crystal shapes on a few of the crystals. It is interesting to note, that after putting this material into water, letting it dissolve, and eventually letting the water evaporate and allowing new crystals to form, the white, dull luster automatically disappears!

Figure 3. Ten “home-grown” crystals of epsomite. The biggest crystal is 27 mm long, 4 mm wide, and 2 mm thick. The shortest crystal is 11 mm long and 2 mm wide.