The new mineral hectorfloresite, known to occur in only one locality in the nitrate fields of northern Chile, consists of tiny prismatic crystals, generally less than 1 mm long and 0.2 mm in diameter, in cavities in dense nitrate ore consisting of saline-cemented silt, sand, and small rock fragments. The cavities also contain euhedral crystals of halite, darapskite, and glauberite. Hectorfloresite is named for Hector Flores W. (1906-1984), a pioneer Chilean geologist.

Hectorfloresite is monoclinic and occurs as pseudohexagonal prismatic crystals consisting of multiple prismatic twins. The space group is P21/a, with a = 18.775(4) Å, b = 6.9356(7) Å, c = 14.239(2) Å, β = 108.91(2)°, and Z = 4[Na9(IO3)(SO4)4]. X-ray powder patterns of natural hectorfloresite show the following strong lines (dmeas, I/I0, hkl): 3.880(100)(411), 2.700(80)(604), 2.788(30)(222), 1.9420(20)(822), 4.69(15)(401), 6.17(10)(011), 1.6800(10)(632), 1.5607(10)(606), and 1.5533(10)(609). Crystal forms are a{100}, c{001), and q{212}. The new mineral has a hardness of about 2, lacks cleavage, and shows a conchoidal fracture. The measured specific gravity of synthetic hectorfloresite is 2.80(3) and the calculated density is 2.90 g/cm3. Hectorfloresite is biaxial negative with a = 1.493(2), β = 1.521(2), and γ = 1.523(2); 2VX = 26(2)°. The new mineral is one of two double salts in the system NaIO3-Na2SO4-H2O. Microprobe analyses of crystals of natural hectorfloresite show the average composition to be 34.5% Na2O, 23.2% I2O5, and 42.3% SO3. Chemical analyses of synthetic hectorfloresite show essentially the same composition. The formula based on these analyses is Na9(IO3)(SO4)4. This composition was confirmed by crystal-structure analysis of natural hectorfloresite.

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