Sauconite

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. 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 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.

Sauconite
Sauconite (reddish brown)
General
CategoryPhyllosilicate mineral
Formula
(repeating unit)		Na0.3Zn3(SiAl)4O10(OH)2·4H2O
IMA symbolSau[1]
Strunz classification9.EC.45
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Identification
ColorReddish brown, brown, brownish yellow, mottled
Crystal habitClayey; as small micaceous plates in laminated to compact masses
CleavagePerfect on {001}
Mohs scale hardness1 - 2
Lusterdull
DiaphaneityTranslucent
Specific gravity2.45
Optical propertiesBiaxial (-)
Refractive indexnα = 1.550 - 1.580 nβ = 1.590 - 1.620 nγ = 1.590 - 1.620
Birefringenceδ = 0.040
Dispersionr > v strong
References[2][3][4]

It was named for the Saucon Valley in Pennsylvania, where it was originally discovered in 1875.[3]

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Mindat
  3. Webmineral data
  4. Handbook of Mineralogy


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