Sauconite is a complex phyllosilicate mineral of the smectite clay group, formula Na0.3Zn3(SiAl)4O10(OH)2·4H2O.

It forms soft earthy bluish white to red-brown monoclinic crystals typically massive to micaceous in habit.

Optically it is biaxial positive with refractive index values of nα = 1.550 – 1.580, nβ = 1.590 – 1.620 and nγ = 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.