Nontronite

Nontronite
Nontronite
	Nontronite from Slovakia
General
Category	Phyllosilicates ; Smectite group
Formula; (repeating unit)	(CaO0.5,Na)0.3Fe3+2(Si,Al)4O10(OH)2·nH2O
IMA symbol	Non
Strunz classification	9.EC.40
Crystal system	Monoclinic
Space group	C2/m (no. 12)
Identification
Color	Yellow, olive-green, green, orange, brown
Crystal habit	Earthy masses
Cleavage	Perfect basal
Fracture	uneven
Mohs scale hardness	1.5 to 2
Luster	Earthy to dull
Streak	Colorless
Specific gravity	2.3
Optical properties	Biaxial (−)
Refractive index	nα = 1.530–1.580; nβ = 1.555–1.612; nγ = 1.560–1.615
Birefringence	δ = 0.030–0.035
References

Nontronite is the iron(III) rich member of the smectite group of clay minerals. Nontronites typically have a chemical composition consisting of more than ~30% Fe₂O₃ and less than ~12% Al₂O₃ (ignited basis). Nontronite has very few economic deposits like montmorillonite.^[6]^[7] Like montmorillonite, nontronite can have variable amounts of adsorbed water associated with the interlayer surfaces and the exchange cations.

A typical structural formula for nontronite is Ca_.5(Si₇Al_.8Fe_.2)(Fe_3.5Al_.4Mg_.1)O₂₀(OH)₄.^[8] The dioctahedral sheet of nontronite is composed mainly of trivalent iron (Fe³⁺) cations, although some substitution by trivalent aluminium (Al³⁺) and divalent magnesium (Mg²⁺) does occur. The tetrahedral sheet is composed mainly of silicon (Si⁴⁺), but can have substantial (about 1 in 8) substitution of either Fe³⁺ or Al³⁺, or combinations of these two cations. Thus, nontronite typically is characterised by having most (usually greater than 60%) of the layer charge located in the tetrahedral sheet. The layer charge is typically balanced by divalent calcium (Ca²⁺) or magnesium (Mg²⁺).

Nontronite forms from the weathering of biotite and basalts, precipitation of iron and silicon rich hydrothermal fluids and in deep sea hydrothermal vents.^[9]^[10] Some evidence suggests that microorganisms may play an important role in their formation.^[11] Microorganisms are also involved in reduction of structural iron in nontronite when soils undergo anoxia, and the reduced form of the clay appears to be highly reactive towards certain pollutants, perhaps contributing to the destruction of these compounds in the environment.^[12]^[13]

The only known commercially viable and operational nontronite mine is located in Canterbury, New Zealand. The mine is operated by Palmer Resources and the finished products are used internationally in industrial applications (pulp & paper, surface coating) and in cosmetics marketed as New Zealand Glacial Clay.^[14]

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.
^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Nontronite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 28 July 2022.
^ Barthelmy, David (2014). "Nontronite Mineral Data". Webmineral.com. Retrieved 28 July 2022.
^ Nontronite, Mindat.org, retrieved 28 July 2022
^ Dainyak, Lidia G.; Zviagina, Bella B.; Rusakov, Viacheslav S.; Drits, Victor A. (2006). "Interpretation of the nontronite-dehydroxylate Mossbauer spectrum using EFG calculations". European Journal of Mineralogy. 18 (6): 753–764. Bibcode:2006EJMin..18..753D. doi:10.1127/0935-1221/2006/0018-0753.
^ Eggleton, R. A. (1977), Clay minerals, vol. 12, pp. 181–194
^ Keeling; et al. (2000). "Geology and Characterization of Two Hydrothermal Nontronites from Weathered Metamorphic Rocks at the Uley Graphite Mine, South Australia". Clays and Clay Minerals. 48 (5): 537–548. Bibcode:2000CCM....48..537K. doi:10.1346/CCMN.2000.0480506. S2CID 129598259.
^ Gates; et al. (2002). "Mountainville nontronite". Clays and Clay Minerals. 50: 223–239. doi:10.1346/000986002760832829. S2CID 95954306.
^ Bischoff (1972), Clays and Clay Minerals, vol. 20, pp. 217–223
^ Eggleton, R. A. (1975). "Nontronite topotaxial after hedenbergite". American Mineralogist. 60: 1063–1068.
^ Kohler; et al. (1994), Clays and Clay Minerals, vol. 42, pp. 680–701
^ Tor, J., C. Xu, J. M. Stucki, M. Wander, G. K. Sims (2000). "Trifluralin degradation under micro-biologically induced nitrate and Fe(III) reducing conditions". Env. Sci. Tech. 34: 3148–3152.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Xu, J., J. W. Stucki, J. Wu, J. Kostka, and G. K. Sims (2001). "Fate of atrazine and alachlor in redox-treated ferruginous smectite". Env. Tox. & Chem. 20: 2717–2724.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ "New Zealand Glacial Clay Fact Sheet". Palmer Resources Limited.