Tarapacáite is the mineral form of potassium chromate with the chemical formula K2CrO4. It forms bright yellow crystals and was discovered in 1878. It is named for the former Tarapacá Province, Peru; nowadays belonging to Chile. The boundaries between Peru, Bolivia and Chile were vague in the Atacama Desert before the War of the Pacific (1879–1883). Its type locality is Oficina Maria Elena, Maria Elena, Tocopilla Province, Antofagasta Region, Chile. It is unlikely to occur anywhere except in highly arid conditions as it is easily soluble in water.[1][2][3]

Tarapacáite
General
CategorySulfate minerals
Formula
(repeating unit)
K2(CrO4)
Strunz classification7.FA.05
Dana classification35.2.1.1.1 Anhydrous chromates
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPnam (no. 62)
Identification
ColorBright yellow, yellow-orange
Crystal habitThick tabular
CleavageDistinct/good
On {001} and {010}, distinct
DiaphaneityTransparent
Specific gravity2.735
SolubilitySoluble in water
Other characteristicsHealth risks: contains the carcinogenic and mutagenic chromate ion
References[1]

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