Sauconite

(repeating unit)Na_0.3Zn₃(SiAl)₄O₁₀(OH)₂·4H₂OIMA symbolSau^[1]Strunz classification9.EC.45Crystal systemMonoclinicCrystal classPrismatic (2/m)
(same H-M symbol)Space groupC2/mIdentificationColorReddish brown, brown, brownish yellow, mottledCrystal habitClayey; as small micaceous plates in laminated to compact massesCleavagePerfect on {001}Mohs scale hardness1–2LusterdullDiaphaneityTranslucentSpecific gravity2.45Optical propertiesBiaxial (−)Refractive indexn_α = 1.550 – 1.580 n_β = 1.590 – 1.620 n_γ = 1.590 – 1.620Birefringenceδ = 0.040Dispersionr > v strongReferences^[2][3][4]

Sauconite is a complex phyllosilicate mineral of the smectite clay group, formula Na_0.3Zn₃(SiAl)₄O₁₀(OH)₂·4H₂O. It forms soft earthy bluish white to red-brown monoclinic crystals typically massive to micaceous in habit. It has a Mohs hardness of 1 to 2 and a specific gravity of 2.45. Optically it is biaxial positive with refractive index values of n_α = 1.550 – 1.580, n_β = 1.590 – 1.620 and n_γ = 1.590 – 1.620.^[2][4] It is found in vugs and seams in the oxidized zones of zinc and copper deposits. It occurs in association with hemimorphite, smithsonite, chrysocolla, coronadite and various iron oxides.

It was named for the Saucon Valley in the Lehigh Valley region of eastern Pennsylvania, where it was originally discovered in 1875.^[3]

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