Fraipontite

(Zn,Al)₃(Si,Al)₂O₅(OH)₄IMA symbolFpt^[1]Strunz classification9.ED.15Crystal systemMonoclinicCrystal classDomatic (m)
(same H-M symbol)Space groupCmUnit cella = 5.34, b = 9.21
c = 14.12 [Å]; β = 93.2°; Z = 2IdentificationColorBlueish, yellow white light greenCrystal habitFibrous to porcelaneous massiveMohs scale hardness3.5 – 4LusterSilkyStreakWhite to pale greenDiaphaneityOpaque to translucentSpecific gravity3.08 – 3.10Optical propertiesBiaxial (-)Refractive indexn_α = 1.620 n_β = 1.624 n_γ = 1.624Birefringenceδ = 0.0042V angleMeasured: 15° to 20°References^[2]^[3]^[4]

Fraipontite is a zinc aluminium silicate mineral with a formula of (Zn,Al)₃(Si,Al)₂O₅(OH)₄.^[2]^[3]

It is a member of the kaolinite-serpentine mineral group and occurs as an oxidation product of zinc deposits. It occurs with smithsonite, gebhardite, willemite, cerussite and sauconite.^[2]

It was first described in 1927 for an occurrence in Vieille Montagne, Verviers, Liège Province, Belgium.^[3] It was named for Julien Jean Joseph Fraipont (1857–1910), and Charles de Fraipont, geologists of Liege, Belgium.^[4] In addition to the type locality in Belgium, it has been reported from Tsumeb, Namibia; Laurium, Greece; Swaledale, North Yorkshire, England; the Silver Bill mine, Cochise County, Arizona, the Blanchard Mine, Socorro County, New Mexico and the Mohawk mine, San Bernardino County, California in the US; and from the Ojuela mine, Mapimi, Durango, Mexico.^[2]

A synonym of the fraipontite is the zinalsite, which was reported in 1956 for an occurrence in Kazakhstan.^[5]^[6]

References

^ 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.
^ ^a ^b ^c ^d Handbook of Mineralogy
^ ^a ^b ^c Mindat.org
^ ^a ^b Webmineral data for fraipontite
^ Zinalsite on Webmineral
^ Zinalsite on Mindat