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Liesegang rings (geology)
Liesegang rings (geology)
Liesegang rings (geology)
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Typical Liesegang ring structures within cross-section

Liesegang rings (/ˈliːzəɡɑːŋ/) (also called Liesegangen rings or Liesegang bands) are colored bands of cement observed in sedimentary rocks that typically cut across bedding.[1][2] These secondary (diagenetic) sedimentary structures exhibit bands of (authigenic) minerals that are arranged in a regular repeating pattern.[3] Liesegang rings are distinguishable from other sedimentary structures by their concentric or ring-like appearance. The precise mechanism from which Liesegang rings form is not entirely known and is still under research,[4] but there is a precipitation process that is thought to be the catalyst for Liesegang ring formation, referred to as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle.[5] Though Liesegang rings are considered a frequent occurrence in sedimentary rocks,[6] rings composed of iron oxide can also occur in permeable igneous and metamorphic rocks that have been chemically weathered.[7]

Liesegang Rings in Volcano-sedimentary Rock from the Gobi Desert of Mongolia. Polished sample 15x9 cm.

History

[edit]

In 1896, a German Chemist named Raphael E. Liesegang first described Liesegang banding in his observations from the results of an experiment, and Wilhelm Ostwald provided the earliest explanation for the phenomenon.[8][9][10][11] The purpose of Liesegang's experiment was to observe precipitate formation resulting from the chemical reaction produced when a drop of silver nitrate solution was placed onto the surface of potassium dichromate gel. The resultant precipitate of silver dichromate formed a concentric pattern of rings. Liesegang and successive other workers observed the behavior of precipitates forming rings in sedimentary rocks, hence these features became known as Liesegang rings.[3]

Note that what's almost universally referred to as “Liesegang banding”, representing precipitation lines of iron-rich minerals (e.g., hematite, limonite, goethite, etc.) at and along groundwater chemical interfaces. But, according to Neil Wells of Kent State University, the original concept of Liesegang banding [8] does not match up with what is seen in the rock record. [12]

Mechanism for development

[edit]
Anvil rock in the Shawnee National Forest, Illinois
"Liesegang banding" in sandstone northwest of Nellie, Ohio
“Liesegang banding” developed in a quartzose sandstone AKA “Scenic Sandstone”.

The process by which Liesegang rings develop is not completely understood.[4] Liesegang rings may form from the chemical segregation of iron oxides and other minerals during weathering.[2] One popular mechanism suggested by geochemists is that Liesegang rings develop when there is a lack of convection (advection) and has to do with the inter-diffusion of reacting species such as oxygen and ferrous iron that precipitate in separate discrete bands which become spaced apart in a geometric pattern.[10] A process of precipitation known as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle is known by the geologic community as a probable mechanism for Liesegang ring formation in sedimentary rocks.[5] In this process the "...diffusion of reactants leads to supersaturation and nucleation; this precipitation results in localized band formation and depletion of reactants in adjacent zones."[5] As Ostwald suggests, there is a localized formation of crystal seeds that occurs when the right level of supersaturation is reached, and once the crystal seeds form, the growth of the crystals is believed to lower the supersaturation level of fluids in pore spaces surrounding the crystals, thus mineralization that occurs after the initial crystal growth in the surrounding areas develops in bands or rings.[10] One classic example based on the Ostwald-Liesegang hypothesis is observed in water and rock interactions where iron hydroxide precipitates in sandstone through pore space.[10]

Liesegang rings in rhyolite (Kofa Mountains, SW Arizona)

Occurrence in the environment

[edit]

Liesegang ring patterns are considered to be secondary (diagenetic) sedimentary structures, though they are also found in permeable igneous and metamorphic rocks that have been chemically weathered.[7] Chemical weathering of rocks that leads to the formation of Liesegang rings typically involves the diffusion of oxygen in subterranean water into pore space containing soluble ferrous iron.[7] Liesegang rings usually cut across layers of stratification and occur in many types of rock, some of which more commonly include sandstone and chert.[3] Though there is a high occurrence of Liesegang rings in sedimentary rocks,[6] relatively few scientists have studied their mineralogy and texture in enough detail to write more about them.[13] Liesegang rings are referred to as examples of geochemical self-organization, meaning that their distribution in the rock does not seem to be directly related to features that were established prior to Liesegang ring formation.[14] For instance, in certain types of sedimentary rocks such as carbonate siltstones (calcisiltites), Liesegang ring patterns can be misinterpreted for faults; the rings may appear to be "offset," however the laminae in the rock exhibit an unbroken pattern, therefore the observed offset is attributed to pseudofaulting.[7] Pseudofaults are the result of Liesegang rings developing within areas of the rock that are adjacent to each other but at varying stratigraphic levels.[7] Liesegang rings can have the appearance of fine lamination and can be mistaken for laminae when parallel or subparallel to the bedding plane, and are more easily differentiated from laminae when the rings are observed cutting across beds or lamination.[2]

References

[edit]
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Liesegang rings (geology)

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Liesegang rings are periodic structures characterized by concentric bands or rings of minerals, formed through reaction- processes in geological media such as porous rocks or sediments. These patterns arise from the diffusion of reactive , leading to rhythmic and of insoluble compounds, often iron oxides like or silica, resulting in visually striking, spaced banding that transcends original sedimentary layering. In geological contexts, they typically develop during or hydrothermal alteration, where gradients in ion concentration drive cycles, producing bands that follow spacing laws such as logarithmic increases in width and separation. The formation mechanism, often explained by the Ostwald supersaturation-nucleation theory combined with diffusion models like the Prager-Silberberg framework, involves an initial wavefront of reacting that depletes the medium, followed by periodic re-supersaturation as fresh reactants diffuse in. In sedimentary rocks, oxygenated percolates through fractures or pores, mobilizing and redepositing metals like iron from host minerals, creating concentric rings around sites such as or fractures. Geometric heterogeneity in the rock matrix, including pore size variations or initial reactant distributions, influences pattern morphology, leading to diverse forms like spherical rings, planar bands, or even polygonal networks. Experimental analogs in gels confirm these processes occur under low-flow, diffusion-dominated conditions, mirroring natural systems without requiring . Geologically, Liesegang rings are prevalent in sandstones, where they manifest as reddish-brown bands cutting across , as seen in the Jurassic of the . They also appear in igneous rocks as orbicular textures in granites or agates, with concentric silica layers forming via similar in vesicular basalts or rhyolites. In fossil-bearing sediments, diagenetic Liesegang rings can mimic biological structures, such as radial patterns in soft tissues or coprolites, composed of precipitated shortly after burial in organic-rich matrices. These features provide insights into post-depositional fluid flow, mineralization history, and in geochemical systems, aiding paleoenvironmental reconstructions. Named after German photographer and chemist Raphael Eduard Liesegang, who first described the phenomenon in 1896 through experiments with in , these patterns have since been recognized across disciplines for exemplifying non-equilibrium . In , their study dates to the early , with applications in genesis, such as rhythmic zoning in deposits, highlighting their role in understanding episodic precipitation in .

Description

Definition

Liesegang rings are secondary structures in rocks, often formed during in sedimentary rocks or through hydrothermal alteration in igneous and metamorphic rocks, characterized by concentric or parallel bands of authigenic minerals, most commonly iron oxides such as or , that form rhythmic, repeating patterns within rocks. These structures arise from the of minerals in a periodic manner, typically during the alteration of rocks after initial formation. Unlike primary sedimentary layering, which parallels planes and forms during deposition, Liesegang rings transect and develop post-formationally through the interaction of with the host rock. This cross-cutting relationship highlights their origin as a later-stage modification rather than a depositional feature. The bands of Liesegang rings generally range from millimeters to centimeters in width, creating cylindrical, spherical, or planar configurations that fill pores, fractures, or voids in the surrounding rock matrix. These patterns emerge from rhythmic precipitation driven by diffusion-reaction processes in geochemical environments. The term "Liesegang rings" derives from the chemical banding phenomenon first documented by German chemist Raphael Eduard Liesegang in 1896, later adapted to describe analogous geological formations.

Characteristics

Liesegang rings exhibit a distinctive visual appearance characterized by concentric or ring-like bands of color, often in shades of red, brown, or yellow derived from iron oxides such as and . These structures typically form cylindrical patterns in cross-section, resembling tree rings or pipe-like features, with alternating dark, mineral-rich bands separated by lighter, unaltered zones of host rock. In some cases, they manifest as linear or septa-like walls, particularly in fractured or porous media. The mineral composition of Liesegang rings primarily consists of iron-bearing minerals, including , , and , which precipitate in rhythmic layers within the host rock. Variations include silica-rich forms such as in agates, manganese oxides in certain nodules, and carbonates in sedimentary settings, with the precipitated bands distinctly separated by unaltered host material. These compositions reflect selective precipitation from diffusing solutions, often involving pseudomorphic replacement of original minerals in the host. While most common in sedimentary rocks with iron oxides, variations include silica-rich forms in igneous-related agates. Texturally, Liesegang rings display sharp boundaries between the precipitated bands and the surrounding host rock, with band spacing that generally increases outward from the reaction front, following patterns like the Jablczynski spacing law. The structures lack a preferred orientation relative to sedimentary , often aligning parallel to fractures or pores instead. Needle-shaped or fine-scale layering may occur within bands, enhancing their rhythmic appearance due to periodic cycles. Variations in Liesegang rings include planar bands in layered sedimentary rocks versus spherical or nodular forms in porous media, with scales ranging from millimeters in chert nodules to decimeters (up to 10-20 cm) in exposures. Double or triple ring patterns can appear in specific deposits like , while wavy or nucleation-centered types follow local fractures or planes.

History

Discovery and naming

The periodic precipitation phenomenon underlying Liesegang rings was first documented in 1896 by German chemist and photographer Eduard Liesegang during laboratory experiments involving the diffusion of into a matrix containing , resulting in concentric rings of insoluble . This observation appeared in his initial publication Chemische Fernwirkung and was further explored for its geological relevance in his 1913 book Geologische Diffusionen, where he suggested analogies to banded mineral structures in rocks. The term "Liesegang rings" originated from this chemist's surname and gained traction in geological contexts starting in the early , particularly after Liesegang's 1915 work Die Achate, which applied the mechanism to explain rhythmic banding in agates and other siliceous rocks. The first explicit geological descriptions of such ring-like bands in sedimentary rocks date to around 1913. The concept saw broader adoption in during the 1920s and 1930s. Initially, these natural bands were often misinterpreted as biogenic remnants or infillings along faults or joints, only later accepted as products of inorganic chemical driven by .

Early scientific explanations

Following the discovery of periodic patterns in 1896, proposed the first comprehensive explanation in 1897, attributing the formation of Liesegang rings to a cycle of , , and depletion during the diffusion of reactants. In this model, one reactant diffuses into a medium containing the other, and occurs only when the product concentration exceeds the supersaturation threshold, triggering sites that rapidly consume the reactants and create a depleted zone ahead, allowing the process to repeat periodically. This theory emphasized chemical as the driving force, without invoking external periodic influences. Raphael Liesegang extended these chemical principles to geological settings in his 1915 publication Die Achate, applying the rhythmic precipitation mechanism to explain banded structures in agates and other rocks. He posited that silica-rich host rocks could behave like the gelatinous media used in experiments, facilitating gel-like and periodic deposition of minerals such as iron oxides or silica. Liesegang's work marked an early bridge between observations and natural geological phenomena, suggesting that post-depositional fluid migration through porous rocks could generate such patterns. During the and , significant debates arose regarding the underlying mechanisms, particularly between diffusion-based theories and those involving colloidal migration. Proponents of the , building on Ostwald's framework, argued that reactant transport alone sufficed to produce the periodicity, as formalized in the spacing law identified by Jablczynski in 1923, which described the of band intervals. In contrast, colloidal theories suggested that fine precipitate particles formed initially and then migrated through the medium before aggregating, a view explored in works like those of Shemyakin in . E.S. Hedges' 1932 review highlighted these competing ideas, noting their implications for interpreting rhythmic deposits in sediments. Early explanations faced limitations, including discrepancies between the concentric rings typical in controlled gel experiments and the more linear or planar bands observed in natural rocks, which often aligned with fractures or planes. Researchers like Liesegang rejected rhythmic —periodic layering during deposition—as the primary cause, favoring instead post-depositional precipitation driven by fluid infiltration, though this left unresolved questions about scaling from lab to field conditions.

Formation Mechanisms

Chemical processes

The formation of Liesegang rings in geological settings is primarily governed by the Ostwald-Liesegang model, which describes periodic through coupled reaction- processes. In this model, a primary reactant, such as Fe²⁺ ions from reducing , diffuses into a medium containing a secondary reactant, like O₂ in an oxidizing environment, leading to localized and discrete events that produce banded precipitates at regular intervals. This results in rhythmic structures, such as bands in sandstones, where the interplay of diffusion gradients and reaction kinetics creates self-organized patterns without external templating. A classic example involves the oxidation of ferrous iron to ferric iron, which precipitates as insoluble hydroxides or oxides forming the rings. The simplified reaction is: 4Fe2++O2+4H+→4Fe3++2H2O4\mathrm{Fe}^{2+} + \mathrm{O}_2 + 4\mathrm{H}^{+} \rightarrow 4\mathrm{Fe}^{3+} + 2\mathrm{H}_2\mathrm{O} This redox process generates Fe³⁺ species that hydrolyze to form precipitates like goethite (α-FeOOH) or hematite (α-Fe₂O₃), concentrating in bands parallel to the diffusion front. The reaction is favored in oxidizing zones where oxygen acts as the electron acceptor, driving the periodic deposition observed in red beds and other permeable rocks. Central to the model is the -depletion cycle, where initial at a front rapidly depletes local reactant concentrations, establishing a zone of undersaturation that inhibits further nearby. then replenishes the reactants ahead of the front, allowing to build again and initiate the next band, with the cycle repeating to form the characteristic spacing. This autoinhibitory mechanism ensures the periodicity, with band spacing often increasing geometrically with distance from the source, as predicted by the model's equations. The role of pH and associated ions is crucial for mobilizing and precipitating iron. Acidic conditions ( ~3.5–5) enhance Fe²⁺ solubility and transport in , while a shift to neutral or slightly alkaline oxidizing environments promotes Fe³⁺ and . Common in sulfate- or chloride-rich fluids, these ions stabilize the reduced iron during until oxidation triggers band formation. Modern experimental validations, particularly post-2000 studies, have replicated these processes in laboratory gels to mimic natural gradients. For instance, or media with controlled Fe²⁺ into oxygenated solutions produce banded iron hydroxides, confirming the nucleation-depletion dynamics and sensitivity to under simulated geological flows. These simulations demonstrate how minor variations in reactant concentrations yield patterns analogous to those in sandstones, supporting the model's applicability to field observations.

Physical and environmental factors

Liesegang rings require host rocks with sufficient and permeability to enable the of aqueous solutions through the matrix. Sedimentary rocks such as sandstones and limestones are ideal, as their interconnected pore networks and grain frameworks allow for the slow migration of solutes over distances of millimeters to centimeters. In these media, primary from depositional fabrics is often supplemented by secondary features like microfractures, which act as preferential pathways for fluid ingress and concentrate along specific planes. For instance, in quartz-dominated sandstones of the Paraíba Basin, permeability variations from 10^{-3} to 10^2 Darcy across fault zones control the of rings. The timing of Liesegang ring development is predominantly diagenetic, occurring post-burial during early to late stages of sediment compaction when pore waters are still mobile. This process can extend into regimes near the surface, particularly in unconsolidated or friable beds where meteoric fluids interact with the rock. Formation is frequently associated with in vadose (unsaturated) or (saturated) zones, spanning timescales from thousands to millions of years, as evidenced in sandstones where rings predate major cementation events. In faulted settings, late-stage reactivation of structures provides episodic fluid pulses that initiate or enhance patterning. Environmental triggers for Liesegang rings include oxidizing conditions arising from the infiltration of oxygen-bearing meteoric waters, which penetrate via fractures and drive in otherwise reducing subsurface environments. Near-surface settings favor this due to cooler temperatures that decrease mineral solubility and promote , while elevated pressures in deeper burial may suppress it by stabilizing dissolved species. These factors are particularly evident in arid to temperate climates where episodic rainfall replenishes vadose zones, as seen in sandstones where surface waters exploit secondary . Band spacing in Liesegang rings scales with distance, typically increasing outward from the reaction front in a manner proportional to the of the product of coefficient and time, resulting in patterns from millimeter-thick rings to centimeter-scale separations. This reflects the physical constraints of solute transport in heterogeneous media, where wider spacing occurs in more permeable zones. Significant gaps persist in understanding Liesegang ring variability, largely attributable to heterogeneous rock fabrics such as irregular distributions and fault-induced permeability contrasts, which can distort ideal banding. Modern research on examples underscores how such fabrics influence pattern fidelity, while emerging studies suggest microbial activity may contribute in organic-rich settings by modulating fluid chemistry through biogenic oxidation, though direct evidence remains limited. Recent modeling (as of 2024) incorporates effects to explain Liesegang-like patterns in features such as Zebra rocks.

Occurrences

Geological settings

Liesegang rings primarily form in permeable sedimentary rocks, such as sandstones, cherts, and limestones, where porous structures facilitate the of reactive fluids. They also occur in igneous rocks like rhyolites and basalts, as well as in metamorphic rocks subjected to hydrothermal alteration or chemical , though less commonly due to lower permeability in these lithologies. These structures develop in environmental contexts characterized by arid or semi-arid regions undergoing intense chemical weathering, often within vadose zones of fluvial or eolian deposits that promote episodic fluid infiltration. Formation predominantly occurs during diagenetic stages in to sediments, reflecting post-depositional alteration under oxidizing conditions; they are rare in rocks owing to limited atmospheric oxygenation that hindered widespread precipitation. Liesegang rings are frequently associated with unconformities or paleosols, serving as indicators of paleoenvironmental conditions such as fluctuating water tables that drove gradients. Recent studies highlight their increasing recognition in , where they enhance permeability and may link to reservoirs by altering fluid flow pathways in porous volcanic frameworks.

Notable examples

One prominent display of Liesegang rings occurs in the Recreation Area, , USA, where concentric rings are etched into the Pennsylvanian-age Caseyville Formation . These rings, up to several centimeters in diameter, formed through post-depositional diagenetic processes involving iron-rich and oxidation during or after , creating vivid reddish-brown patterns that enhance the area's dramatic hoodoo landscapes. In the arid expanses of the , , Liesegang rings manifest as linear bands within volcano-sedimentary rocks, resulting from episodic groundwater flow through porous layers under hyper-arid conditions. A well-preserved example, collected in 1983, features polished sections revealing sharp, parallel precipitates up to 15 cm across, illustrating how and drive banding in eolian-influenced settings. Liesegang rings occur in the Buntsandstein sandstones of , with cylindrical patterns emerging from rhythmic cementation along fractures. These structures exemplify diagenetic alteration in continental . Recent discoveries underscore the temporal range of Liesegang rings, including rare occurrences in sandstones of the Indian craton. A 2023 study identified concentric bands in the Upper Bhander of the Vindhyan Supergroup, , where their preservation is exceptional given the era's low atmospheric oxygen levels, which limited widespread oxidation and precipitation. Similarly, Liesegang banding contributes to the concentric layers lining geodes in Paraná Basin volcanic rocks, , where silica in gas vesicles produces colorful, radially fibrous walls up to 30 cm in diameter during hydrothermal activity.

References

  1. https://www.researchgate.net/publication/304782315_Liesegang_Patterns_in_Nature_A_Diverse_Scenery_Across_the_Sciences_a_review_paper
  2. https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2025.1628328/full
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7811783/
  4. https://pubs.geoscienceworld.org/geosocindia/jour-geosocindia/article/99/12/1716/632112/The-Occurrence-of-Rare-Liesegang-Rings-in-the
  5. https://www.mindat.org/glossary/liesegang_banding
  6. https://digitalcommons.unl.edu/geosciencefacpub/537
  7. https://www.sciencedirect.com/science/article/abs/pii/S0169555X97000421
  8. https://pmc.ncbi.nlm.nih.gov/articles/PMC7811783/
  9. https://www.insilico.hu/liesegang/history/history.html
  10. https://pubs.acs.org/doi/10.1021/acs.langmuir.9b03018
  11. https://www.mdpi.com/2075-163X/10/11/953
  12. https://depositsmag.com/2015/12/23/origin-of-agate-a-300-year-old-enigma/
  13. https://www.govinfo.gov/content/pkg/GOVPUB-C13-3232039058a0db13e5cdc18dc223b008/pdf/GOVPUB-C13-3232039058a0db13e5cdc18dc223b008.pdf
  14. https://www.nature.com/articles/srep10792
  15. https://pubs.geoscienceworld.org/gsa/gsabulletin/article/125/5-6/913/125932/Structural-control-on-the-formation-of-iron-oxide
  16. https://www.wsgs.wyo.gov/products/wsgs-1977-r-33.pdf
  17. https://www.researchgate.net/publication/376650259_The_Occurrence_of_Rare_Liesegang_Rings_in_the_Neoproterozoic_Upper_Bhander_Sandstone_Vindhyan_Supergroup_Rajasthan
  18. https://www.researchgate.net/publication/281083516_Life_and_Liesegang_Outcrop-Scale_Microbially_Induced_Diagenetic_Structures_and_Geochemical_Self-Organization_Phenomena_Produced_by_Oxidation_of_Reduced_Iron
  19. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JB029379
  20. https://www.scielo.br/j/lajss/a/JZJQD8xMTH9js5DSCkRpKdS/?lang=en
  21. https://onlinelibrary.wiley.com/doi/abs/10.1111/sed.13135
  22. https://www.researchgate.net/publication/258787034_Structural_control_on_the_formation_of_iron-oxide_concretions_and_Liesegang_bands_in_faulted_poorly_lithified_Cenozoic_sandstones_of_the_Paraiba_Basin_Brazil
  23. https://scholarshare.temple.edu/bitstreams/ee7de6ad-b0c0-42fd-b8cf-bd11b4987f2e/download
  24. https://www.dnr.wa.gov/Publications/ger_b75_geol_wenatchee_monitor.pdf
  25. https://pubs.geoscienceworld.org/gsa/gsabulletin/article/127/11-12/1711/126125/Mineral-reactions-associated-with-hydrocarbon
  26. https://library.isgs.illinois.edu/Pubs/pdfs/ftgb/ftgb2009B-gardenofthegods.pdf
  27. https://imaggeo.egu.eu/view/1948/
  28. https://crimsonpublishers.com/boj/pdf/BOJ.000525.pdf
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