Sanderite
Chemical formula: MgS<sup>6+</sup>O<sub>4</sub>·2H<sub>2</sub>O
Sanderite is a historical name for magnesium sulfate dihydrate, now recognized as a partially dehydrated form of epsomite.
Description
## Characteristics Sanderite is not a recognized mineral species but a historical name for magnesium sulfate dihydrate (MgSO₄·2H₂O). In nature, it occurs as a dehydration product of epsomite (MgSO₄·7H₂O). It typically forms white, fine-grained or powdery coatings and crusts, as well as fibrous efflorescences on rock surfaces or on old museum specimens of epsomite. ## Physical Properties Due to its nature as an intermediate product, its properties are difficult to precisely determine. It is a very soft and brittle substance. The luster is most often earthy or dull. It is significantly less dense than most rock-forming minerals. ## Colors and Varieties Sanderite is usually white, less commonly colorless. It does not form colored or commercial varieties. ## History and Name The name was given in 1913 by Friedrich Martin Berwerth in honor of Bruno Sander, professor of mineralogy at the University of Innsbruck. The mineral was disqualified by the International Mineralogical Association (IMA) in 1981 when its identity with “leonhardite” was established, which in turn was also later disqualified as an intermediate form of epsomite.
Diagnostic features
## Identification The key characteristic is its mode of occurrence – white, powdery or fibrous efflorescences on or near epsomite. It is water-soluble and has a bitter-salty taste (tasting minerals is discouraged). Definitive identification requires X-ray diffraction (XRD) analysis to determine the degree of hydration. ## Distinguishing from Similar Minerals It can be confused with other white, soluble sulfates such as epsomite, hexahydrite, goslarite, or melanterite. Distinguishing it “by eye” is practically impossible and relies mainly on the geological context (as a dehydration product of epsomite). ## Crystal Forms It does not form well-developed crystals. It occurs as microcrystalline aggregates, coatings, and crusts.
Geological environment
## Genesis It is a secondary mineral, formed exclusively by the partial dehydration of epsomite under low humidity conditions. It forms as efflorescences on mine walls, in caves, and on the surface of epsomite specimens stored in dry museum or collector conditions. ## Mineral Associations It occurs almost exclusively in association with epsomite, from which it forms. It may co-occur with other magnesium sulfates with varying degrees of hydration, such as hexahydrite. ## Localities The type locality, from which it was originally described, is Grotto di Vetriolo in Trento, Italy. Its occurrence is potentially possible wherever epsomite undergoes dehydration.
Rarity
Rare
Collector aspects
## Quality Criteria It is not a mineral sought after by collectors as a distinct species. Specimens documenting the process of epsomite transforming into its less hydrated forms may have collector value, serving more as a mineralogical curiosity.
Care and storage
## Cleaning Cleaning is not recommended. The mineral is water-soluble and very brittle. Any attempt at wet cleaning will destroy the specimen. ## What to Avoid Contact with water and high humidity, which will cause rehydration to epsomite, must be strictly avoided. Too dry air can lead to further dehydration. It is susceptible to mechanical damage. ## Storage “Sanderite” specimens require storage under stable conditions. The best solution is a tightly sealed container (e.g., a “membrane box” type) or a display case away from sources of moisture and temperature fluctuations.