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Hanksite crystal from Searles Lake
CategorySulfate minerals
(repeating unit)
Strunz classification7.BD.30
Crystal systemHexagonal
Crystal classDipyramidal (6/m)
H–M symbol: (6/m)
Space groupP63/m
Unit cella = 10.465(21) Å
c = 21.191(43) Å; Z = 2
ColorColorless to pale yellow, may be grayish green due to clay inclusions
Crystal habitOccurs as short prismatic to tabular hexagonal crystals
CleavageGood on {0001}
Mohs scale hardness3–3.5
LusterVitreous to dull
DiaphaneityTransparent to translucent
Specific gravity2.562
Optical propertiesUniaxial (−)
Refractive indexnω = 1.481, nε = 1.461
Birefringenceδ = 0.020
Ultraviolet fluorescencePale yellow under LW UV
SolubilityReadily soluble in water

Hanksite is a sulfate mineral, distinguished as one of only a handful that contain both carbonate and sulfate ion groups. It has the chemical formula Na22K(SO4)9(CO3)2Cl.


It was first described in 1888 for an occurrence in Searles Lake, California and named for American geologist Henry Garber Hanks.[2][3] Hanksite is normally found in crystal form as evaporite deposits. Hanksite crystals are large but not complex in structure, it is often found in Searles Lake, Soda Lake, Mono Lake, and in Death Valley. It is associated with halite, borax, trona and aphthitalite in the Searles Lake area,[1] it is also associated with borax mining in the Soda Lake area.[citation needed]

Physical characteristics[edit]

Hanksite can be colorless, white, gray, green or yellow and is transparent or translucent; the mineral's hardness is approximately 3 to 3.5. The specific gravity is approximately 2.5 (slightly below average). It is salty to the taste and sometimes glows pale yellow in ultraviolet light. Typical growth habits are hexagonal prisms or tabular with pyramidal terminations; the streak of Hanksite is white. It can contain inclusions of clay that the crystal formed around while developing.

Similar minerals[edit]