Tiny particles building huge ore deposits – Particle-based crystallisation in banded iron formation-hosted iron ore deposits (Hamersley Province, Australia)

Mineralogy of Vera Rubin Ridge From the Mars Science Laboratory CheMin Instrument

“…Gray hematite (also called specular or microplaty hematite; Lane et al, 2002) is typically coarser‐grained than red hematite, where hematite with grain sizes %3C ~5 μm appear red to the human eye and coarser hematite grains > ~5 μm appear black or gray (e.g., Catling & Moore, 2003; Morris et al, 2020). Large particles made up of aggregates of ~10–200 nm hematite crystallites can appear gray or black (Egglseder et al, 2019; Madden et al, 2010). Gray hematite has been found to form by many different mechanisms (Catling & Moore, 2003), including crystallization from ferrihydrite in aqueous hydrothermal environments at ~100–200°C, precipitation in acid‐sulfate hydrothermal solutions from the breakdown of jarosite (Golden et al, 2008), vapor phase condensation in fumaroles, and high‐temperature oxidation of basalts (e.g., Minitti et al, 2005).…”

“…Gray hematite has been found to form by many different mechanisms (Catling & Moore, 2003), including crystallization from ferrihydrite in aqueous hydrothermal environments at ~100–200°C, precipitation in acid‐sulfate hydrothermal solutions from the breakdown of jarosite (Golden et al, 2008), vapor phase condensation in fumaroles, and high‐temperature oxidation of basalts (e.g., Minitti et al, 2005). Gray hematite has been identified in banded iron formations, in which it may form from a variety of mechanisms, including transformation from ferrihydrite at low‐grade metamorphic temperatures (e.g., Sun et al, 2015) and dissolution of hematite‐bearing quartz layers by warm, saline solutions, resulting in the aggregation of hematite nanoparticles into millimeter‐scale hematite bands (Egglseder et al, 2019). The dehydration of large (>1 μm) goethite crystallites, generally at temperatures >80°C, can produce large hematite crystallites that maintain the acicular goethite morphology (Weibel & Grobety, 1999).…”

Particle-based hematite crystallization is invariant to initial particle morphology

“…The combined experimental observations and theoretical predictions highlight aspects of the OA mechanism that strong face specificity along one crystallographic direction can render the OA to be independent of particle morphology. The findings thus provide insights for understanding the formation of certain unique crystallization patterns observed in natural systems, in this case particularly 1D structures such as those observed in the growth of microplaty hematite crystallites that comprise nano- or microsized particles in hematite ores located at Hamersley Province, Australia ( 11 ). They also provide a basis for understanding the formation of oriented biominerals (e.g., modern and fossil nacre from molluscans) ( 73 ) and nanowires/chains/rods/needles [e.g., PbSe ( 74 ), CdSe ( 75 ), ZnO ( 35 , 52 ), and hematite 1D materials ( 34 )] with particle-based morphologies.…”

“…As one of the most important physicochemical processes, crystallization plays key roles in geochemical and biological processes and in materials synthesis ( 1 – 11 ). With the development of in situ characterization and its expansion into more complex systems, numerous nonclassical crystallization phenomena, i.e., crystallization processes that do not involve monomer-by-monomer addition, were observed ( 3 , 5 , 6 , 12 – 23 ).…”

“…Among various particle-based crystallization phenomena, oriented attachment (OA) of crystalline particles has attracted particular attention ( 14 , 24 – 33 ). To date, OA has been observed in a wide range of synthetic systems and natural environments ( 3 , 5 , 6 , 11 , 12 , 14 , 15 , 20 , 24 , 25 ). Moreover, OA has shown enormous potential in synthesizing single crystals with well-defined size and a wide variety of crystal morphologies including chains ( 34 ), nanorods ( 35 , 36 ), nanosheets ( 37 ), nanocubes ( 38 ), nanowires ( 24 , 39 ), nanobranches ( 40 ), and so on.…”