Hanksite

Hanksite
Hanksite crystal from Searles Lake
General
Category Sulfate minerals
Formula
(repeating unit)		 Na22K(SO4)9(CO3)2Cl
Strunz classification 7.BD.30
Crystal system Hexagonal
Crystal class Dipyramidal (6/m)
H–M symbol: (6/m)
Space group P63/m
Unit cell a = 10.465(21) Å
c = 21.191(43) Å; Z = 2
Identification
Color Colorless to pale yellow, may be grayish green due to clay inclusions
Crystal habit Occurs as short prismatic to tabular hexagonal crystals
Cleavage Good on {0001}
Fracture Uneven
Tenacity Brittle
Mohs scale hardness 3–3.5
Luster Vitreous to dull
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.562
Optical properties Uniaxial (−)
Refractive index nω = 1.481, nε = 1.461
Birefringence δ = 0.020
Ultraviolet fluorescence Pale yellow under LW UV
Solubility Readily soluble in water
References [1][2][3]

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.

Occurrence

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.

Physical characteristics

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

References

  1. 1 2 Handbook of Mineralogy.
  2. 1 2 Mindat.org.
  3. 1 2 Webmineral data.
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