Mendozite is a
sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
mineral, one of the
alum
An alum () is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula , where is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the ...
series, with formula NaAl(SO
4)
2·11H
2O. It is a hydrated form of
sodium aluminium sulfate (soda alum).
It was discovered in western
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
in 1868, probably near
San Juan San Juan, Spanish for Saint John, may refer to:
Places Argentina
* San Juan Province, Argentina
* San Juan, Argentina, the capital of that province
* San Juan, Salta, a village in Iruya, Salta Province
* San Juan (Buenos Aires Underground), ...
. The exact location has been lost, but was described as "San Juan, near
Mendoza", and it is the latter city that give the mineral its name.
It occurs in
evaporites
An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...
, presumably from the
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
of
sulfide mineral
The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the ...
s in the presence of
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay parti ...
s.
It is very soluble in water, and so can only be found in dry regions: however, in can still
effloresce (lose
water of crystallisation) in extremely arid climates,
altering to
tamarugite (the hexahydrate).
References
Bibliography
*
Palache, P.; Berman H.; Frondel, C. (1960). "''Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)"'' John Wiley and Sons, Inc., New York, pp. 469-471.
Sodium minerals
Aluminium minerals
Sulfate minerals
Monoclinic minerals
Minerals in space group 15
{{sulfate-mineral-stub