Formation Of Aragonite Research Articles

Electrochemical Study of Calcareous Deposit Formation in Simulated Soil Solution under Cathodic Protection

Cathodic protection induces the formation of a calcareous layer has been shown to improve metal protection against corrosion by reducing the oxygen diffusion on the metal surface. The present study focuses on the electrochemical scaling induced by the application of cathodic polarisation. A combination of non-invasive in-situ electrochemical techniques and electrochemical impedance spectroscopy was used. Metal/electrolyte interface behaviour was studied using voltammetry to determine the controlling anodic and cathodic reactions. One-week long experiments were conducted. Applied potential –1.2 VSCE was shown to enable the formation of CaCO3 allotropes calcite and aragonite, and brucite due to increased interfacial pH which resulted in the formation of hydrogen at the electrode surface. Time constants from bode plots for applied potential –1.2 VSCE also illustrated the inhomogeneity of the calcareous layer. Modelling of polarisation curves illustrated a “passivation” phenomenon which resulted from formation of hydroxyl cations. This was further validated by bode plots with the added information on the diffusion reaction process. High frequency behaviour showed a steady increase in the electrolyte resistance which may be attributed to the formation of the calcareous layer. Evidence of the initial Mg-gel porous layer, which precedes the formation of brucite, was found.

The role of chitin-rich skeletal organic matrix on the crystallization of calcium carbonate in the crustose coralline alga Leptophytum foecundum

The organic matrix (OM) contained in marine calcifiers has a key role in the regulation of crystal deposition, such as crystalline structure, initiation of mineralization, inhibition, and biological/environmental control. However, the functional properties of the chitin-rich skeletal organic matrix on the biological aspect of crystallization in crustose coralline algae have not yet been investigated. Hence, the characterization of organic matrices in the biomineralization process of this species was studied to understand the functions of these key components for structural formation and mineralization of calcium carbonate crystals. We purified skeletal organic matrix proteins from this species and explored how these components are involved in the mineralization of calcium carbonate crystals and environmental control. Intriguingly, the analytical investigation of the skeletal OM revealed the presence of chitin in the crustose coralline alga Leptophytum foecundum. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the OM revealed a high molecular mass protein as 300-kDa. Analysis of glycosylation activity exposed two strong glycoproteins as 300-kDa and 240-kDa. Our study of the biominerals of live collected specimens found that in addition to Mg-calcite up to 30% aragonite were present in the skeleton. Our experiment demonstrated that the chitin-rich skeletal OM of coralline algae plays a key role in the biocalcification process by enabling the formation of Mg-calcite. In addition, this OM did not inhibit the formation of aragonite suggesting there is an as yet unidentified process in the living coralline that prevents the formation of aragonite in the living skeletal cell walls.

Fine Grain Concrete on Mixing Water Activated in Cavitation Permanent Magnet-Type Apparatus

The authors obtained fine grain concrete based on the mortars of additives-electrolytes undergone mechanic magnetic activation and characterized by improved compression and bending strength and enhanced freeze-thaw resistance. There was investigated the impact of mechanic magnetic activation (MMA) on mixing water when adding calcium chloride and sodium thiosulphate as well as on porosity of cement stone and specific features of phase formation in cement stone. It was stated by the authors that MMA facilitates formation of nucleation centers in activated water in the presence of additives-electrolytes, optimization of porous space as well as crystallization of calcium carbonate in the form of aragonite when lowering the content of Portlandite. The mechanism of joined influence of hydrodynamic and magnetic treatment of mixing water has been determined.

A Short Review on Cockle Shells as Biomaterials in the Context of Bone Scaffold Fabrication

Cockle shells contribute to a large amount of waste product in South East Asia due to the extensive culturing of the mollusc for consumption. These nacreous materials in the recent years have been gaining wider popularity due to its potential use as biomaterials. As shown in various studies, cockle shell powder consists of 95-98% aragonite form of calcium carbonate (CaCO3). The calcium carbonate obtained from cockle shells are easily converted into nanoparticles, which have shown encouraging results in bone tissue grafting. With the recent advancement in bone tissue engineering and development of a newer generation of biomaterial based bone scaffolds, the cockle shell powder has promising applications in the near future to be used in the formulation of bone grafting materials. In this review, the use of biomaterials in bone tissue grafting and nacreous materials as potential biomaterials with a focus on the cockle shell and its recent advancement as the main component in the formulation of a nanobiocomposite bone scaffold is discussed.

Effect of sulfate on magnesium incorporation in low-magnesium calcite

The incorporation of magnesium and sulfate in calcite is frequently used to characterize and trace the environmental conditions occurring during carbonate mineral formation. Although both ions are simultaneously incorporated in the growing calcite, the effect of sulfate on magnesium incorporation in calcite is still under-explored. In this study, we examine the Mg incorporation in low-Mg calcite as a function of growth rate at 25 °C and 1 bar pCO2 in the presence and absence of aqueous sulfate. The obtained results suggest that high calcite growth rates induce a significant increase in the partitioning coefficient of Mg between the precipitated low-Mg calcite and aqueous solution (i.e. DMg=nMg/nCacalcite[Mg2+]/[Ca2+]solution). Obtained DMg values exhibit similar dependence to mineral growth rate for experiments performed in the presence and absence of sulfate, however a systematic shift to lower DMg values is observed for calcites formed in the presence of sulfate. The lower DMg values of calcites formed in sulfate-bearing solutions are attributed to the incorporated SO4 ions which provoke expansion in the unit cell along the c-axis of the newly formed calcite. A larger unit cell is unfavorable for the substitution of Ca by smaller Mg ions in calcite. The coupled effect of (i) sulfate uptake during calcite growth and (ii) precipitation rate on DMg can be expressed by the equation DMg=0.03726-0.02345×-logrp-7-XSO4×0.004607+0.002109×-logrp-7; (−8 ≤ log(rp) ≤ −7; 0 ≤ Xso4 ≤ 2.6; T = 25 °C) and is valid for 0.01 ≤ DMg ≤ 0.04. In analogy to Mg also SO4 ions are inhibiting calcite growth, thus promoting the formation of aragonite due to adsorption phenomena and blocking of calcite surface sites. These results improve our understanding on physicochemical parameters controlling CaCO3 composition and mineral polymorphism and are discussed in their relevance for the use of magnesium and sulfate environmental proxies in natural surroundings.

Aragonite formation induced by open cultures of microbial consortia to heal cracks in concrete: Insights into healing mechanisms and crystal polymorphs

Microbially induced CaCO3 precipitation (MICP), mainly in the form of calcite, has been reported to be an efficient approach for self-healing cracks in concrete. However, little is known about the implementation of aragonite, the other common crystalline form of CaCO3, in bioconcrete. Therefore, a systematic investigation of the crystal polymorphs and the healing efficiency of different cultures, i.e., two microbial consortia under anaerobic (MC-Aa) and anoxic (MC-Ao) conditions and nonureolytic pure-culture bacteria (Bacillus cohnii), was conducted in this study. The results showed that the MC-Ao agent exhibited the maximum values of completely healed crack widths (1.22 mm) after 28 d of healing, which is larger than the values of 0.79 and 0.73 mm for B. cohnii and MC-Aa, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analyses confirmed that the biominerals induced by MC-Aa and B. cohnii are calcite, while those of MC-Ao were 82% aragonite and 18% calcite. It is noteworthy that this proportion of aragonite is the highest reported level for the MICP system to date. In addition, economic evaluation verified that the microbial consortia resulted in a 61% decrease in production costs compared to pure cultures. The intriguing findings obtained in this study may provide a scientific basis for the potential implementation of microbial consortia under anoxic conditions, such as a new self-healing agent, in bioconcrete.

Differential gene expression in skeletal organic matrix proteins of scleractinian corals associated with mixed aragonite/calcite skeletons under low mMg/Ca conditions.

Although coral skeletons generally comprise aragonite crystals, changes in the molar Mg/Ca ratio (mMg/Ca) in seawater result in the incorporation of calcite crystals. The formation mechanism of aragonite and calcite crystals in the scleractinian coral Acropora tenuis was therefore investigated by RNA-seq analysis, using early growth stage calcite (mMg/Ca = 0.5) and aragonite (mMg/Ca = 5.2)-based corals. As a result, 1,287 genes were up-regulated and 748 down-regulated in calcite-based corals. In particular, sixty-eight skeletogenesis-related genes, such as ectin, galaxin, and skeletal aspartic acid-rich protein, were detected as up-regulated, and six genes, such as uncharacterized skeletal organic matrix protein 5, down-regulated, in low-Mg/Ca conditions. Since the number of down-regulated genes associated with the skeletal organic matrix of aragonite skeletons was much lower than that of up-regulated genes, it is thought that corals actively initiate construction of an aragonite skeleton by the skeletal organic matrix in low-Mg/Ca conditions. In addition, different types of skeletal organic matrix proteins, extracellular matrix proteins and calcium ion binding proteins appeared to change their expression in both calcite-formed and normal corals, suggesting that the composition of these proteins could be a key factor in the selective formation of aragonite or calcite CaCO3.

Adsorption/Absorption of Lithium Affecting the Growth Morphology of Aragonite. The Two-Dimensional Epitaxy of Li2CO3 (Zabuyelite) on the {001} Form of Aragonite (CaCO3)

Growing aragonite crystals from aqueous solution in the presence of Li+ ions increases the morphological importance of the {001} pinacoid, both in single and twinned crystals. Owing to the structural similarities between the basal d002 layers of aragonite and the d00.6 layers of calcite and having re-collected the habit modification induced by lithium on calcite crystals nucleated and grown from aqueous solution, an interpretation is given of experimental results on the basis of the adsorption/absorption mechanism of dh0l slices of Li2CO3 (mineral zabuyelite), in the {001} growth sectors of aragonite. Detailed analysis on the coincidence lattices and the evaluation of the specific interface energies allow us to determine that two-dimensional epitaxy occurs between the adsorbed d202 slices of zabuyelite and the outmost 001 layers of the growing aragonite.

Carboxymethylcellulose sodium salt – effective “green” regent for management of calcium carbonate crystallization and nat-ural gas hydrate formation

The effect of carboxymethylcellulose sodium salt (NaCMC) with molecular masses (Mw) of 90, 250 and 700 thousand on the crystallization of CaCO3 polymorphs, their size and deposition on the surface of stainless steel from supersaturated aqueous solution at 80 ° C was studied. As a result of specific reversible adsorption, when forming crystalline nuclei formed, it is assumed that NaCMC changes the shape of the growing crystal, preferably forming vaterite — up to 95% in the presence of NaCMC with a molecular mass of 90 thousand during the in-teraction of CaCl2 and NaHCO3. In the presence of Mg2+ ions, CaCO3 is formed mainly in the form of aragonite, and the influence of the molecular mass of NaCMC is significantly reduced. It was established that NaCMC with Mw 90 and 250 thousand inhibits the aggregation and ag-glomeration of CaCO3 crystals, leading to a decrease in the average size of crystals from 24 to 10.6 and 16.5 microns, respectively. Under the action of NaCMC with a molecular mass of 700 thousand, on the contrary, an increase in the size of crystals to 37.2 μm is observed. It is shown that NaCMC with Mw 90 and 250 thousand slows down the speed and changes the conditions of gas hydrate formation, showing the properties of a thermodynamic and kinetic inhibitor with an efficiency that exceeds methanol by 300-450 times when used in the same dosages. The da-ta obtained indicate the promise of creating new “green” reagents of complex action for oil and gas production on the basis of sodium salt carboxymethylcellulose.

Carbonation of natural pure and impure wollastonite

Wollastonite can be used as cementitious material, for example in carbon capture and storage (CCS application). The interaction of wollastonite (CS) and pure CO2 in the presence of H2O at temperature (333 K) relevant to injection conditions for CCS were investigated within the joint BMWi research project CLUSTER. The reaction which describes the formation of wollastonite during metamorphism, is reversed. Wollastonite reacts in the presence of CO2-pressure under aqueous conditions to form calcium carbonate and amorphous silicon oxide. To determine the driving force for this reaction it is important to investigate the impact of CO2 pressure (p) and temperature (T). The reaction kinetics of the carbonation reaction of wollastonite is strongly dependent to temperature. At 333 K and 2 MPa CO2 the $${\bar{\text{C}}}$$ CS reaction is fast (≤ 24 h). The chemical composition of wollastonite was analyzed by X-ray fluorescence. To determine the conversion rate of the reaction quantitatively powder X-ray diffraction with Rietveld method were applied. For further application, it is important to understand the specific reactions during the carbonation. Therefore, the influence of different treatments on wollastonite raw material (hydrochloric acid, acetic acid and temperature), before the carbonation experiments, on the carbonation reaction were investigated. The conversion of wollastonite, depending on temperature, was performed successfully. It could be proven, that aragonite acted as seed crystal for further aragonite formation. Furthermore, indications for the formation of aragonite out of amorphous CaCO3 were observed.

In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization.

Otoliths are one of the biominerals whose formation is highly controlled by proteins. The first protein discovered to be involved in otolith biomineralization in zebrafish was starmaker (Stm). Previously, Stm was shown to be responsible for the preferential formation of aragonite, a polymorph of calcium carbonate, in otoliths. In this work, proteomic analysis of adult zebrafish otoliths was performed. Stm is the only highly phosphorylated protein found in our studies. Besides previously studied otolith proteins, we discovered several dozens of unknown proteins that reveal the likely mechanism of biomineralization. A comparison of aragonite and vaterite otoliths showed similarities in protein composition. We observed the presence of Stm in both types of otoliths. In vitro studies of 2 characteristic Stm fragments indicated that the DS-rich region has a special biomineralization activity, especially after phosphorylation.-Kalka, M., Markiewicz, N., Ptak, M., Sone, E. D., Ożyhar, A., Dobryszycki, P., Wojtas, M. In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization.

FTIR-Based Crystallinity Assessment of Aragonite–Calcite Mixtures in Archaeological Lime Binders Altered by Diagenesis

Lime plaster and mortar are pyrotechnological materials that have been employed in constructions since prehistoric times. They may nucleate as calcite and/or aragonite under different environmental settings. In nature, aragonite and calcite form through biogenic and geogenic processes that lead to different degrees of atomic order. The latter is a result of defects in the crystal lattice, which affect the properties of crystals, including their interaction with infrared light. Using Fourier transform infrared spectrometry (FTIR) with the KBr pellet method, it is possible to exploit these differences and assess the degree of atomic order of aragonite and calcite crystals and thus their mechanisms of formation. Here we use FTIR to characterize the degree of short-range atomic order of a pyrogenic form of aragonite recently observed in experimental and archaeological lime binders. We show that pyrogenic aragonite has a unique signature that allows its identification in archaeological sediments and lime binders of unknown origin. Based on these results, we developed a new FTIR-based method to assess the integrity and degree of preservation of aragonite and calcite when they occur together in the same material. This method allowed a better assessment of the diagenetic history of an archaeological plaster and finds application in the characterization of present-day conservation materials, such as lime plaster and mortar, where different polymorphs may nucleate and undergo recrystallization processes that can alter the mechanical properties of binders.

Phosphate Enrichment Hampers Development of Juvenile Acropora digitifera Coral by Inhibiting Skeleton Formation.

Coral reef degradation due to various local stresses, such as nutrient enrichment and terrestrial run-off into coastal waters, is an increasing global concern. Inorganic phosphates have been considered to possibly inhibit skeleton formation in corals. Despite many studies available on the effects of nutrients on corals, a clear consensus on how nutrients exert deteriorative effects on corals has not been established satisfactorily. In this study, we examined the effects of phosphates and nitrates on in vitro aragonite CaCO3 formation by using biogenic polyamines and in vivo aragonite formation in the skeleton of juvenile Acropora digitifera corals. We showed that the phosphates at similar concentrations clearly inhibited both in vitro and in vivo CaCO3 formation. In contrast, nitrates inhibited neither in vitro aragonite CaCO3 formation nor in vivo aragonite formation in juvenile coral skeleton. Furthermore, our findings showed that inhibition of coral skeleton formation was due to absorption of phosphate on the skeleton, which inorganically inhibited normal development of juvenile coral skeleton.

Effects of Al2O3 nanoparticles on the formation of inorganic scale on heat exchange surface with and without scale inhibitor

The scale inhibition and mechanism of the scale inhibitor PBTCA (2-phosphonobutane-1,2,4-tricarboxylic acid) on CaCO3 in a scale-forming solution and an Al2O3 nanofluid were investigated by solution scale inhibition, surface scale inhibition, electrical conductivity, scanning electron microscopy, X-ray diffraction, and diffuse reflection Fourier transform infrared spectroscopy. The results showed that PBTCA had good solution scale inhibition performance and surface scale inhibition performance on heat exchange surface in scale-forming solution. In an Al2O3 nanofluid, the solution scale inhibition performance of PBTCA decreased with an increase in nanoparticle concentration. However, the surface scale inhibition performance of PBTCA first decreased and then increased with an increase in Al2O3 nanoparticle concentration, and the surface scale inhibition performance was obviously higher than the solution scale inhibition performance. Al2O3 nanoparticles significantly shortened the induction period of CaCO3 nucleation in the scale-forming solution containing PBTCA, weakening the solubilization of PBTCA on CaCO3 and decreasing the solution scale inhibition of PBTCA, whereas Al2O3 nanoparticles promoted the formation of aragonite and exhibited certain surface scale inhibition performances.

Effect of Aging Time in the Synthesis of Biogenic Hydroxyapatite Derived from Cockle Shell

Abstract Cockle shell wastes are abundant, easily available and can be obtained at low cost. It is rich in calcium carbonate (CaCO3) that can be precursor to synthesis hydroxyapatite (HAP). The HAP has potential to be used in numerous applications such as biomedical and wastewater treatment. The overall objective of this study is to determine the effect of aging time on the production of HAP derived from cockle shells waste. There are two aging times used in this study which are 3 and 5 h. The processes involved in synthesizing HAP were pretreatment of the cockle shells, production of CaCO3 in aragonite form, calcination of the CaCO3 to form CaO, production of Ca(OH)2 and finally reaction of the Ca(OH)2 solution with the phosphate source to obtain HAP. All samples have undergone physicochemical analyses to determine their phases, crystallinity, purity, functional group, surface morphology and elemental analysis using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM) and Electron Dispersive X-ray Analysis (EDX). This study found that 5 h aging time produced higher crystalline HAP compared to the others. Overall, this study proved that aging time play vital role in the quality of the synthesized HAP.

Pharmaceutical Standardization and Physicochemical Characterization of Traditional Ayurvedic Marine Drug: Incinerated Conch Shell (Shankha Bhasma)

Natural resources such as plants, animals and minerals have always been used by mankind to develop drugs and marine world is no exception. Marine by-products like conches, pearls, mother of pearl shells, corals and so forth have been used by traditional Ayurvedic practitioners for centuries. The unique methods of these preparations are scientifically designed to eliminate unwanted impurities and convert them into bioavailable form. In this study, Conch (Xanchus pyrum) was used as a marine resource of calcium carbonate and was converted pharmaceutically from its aragonite form to calcite. All the steps of preparations and changes in the properties therein were documented and validated. Further, traditional as well as modern analytical tools were used to study its physical and chemical characters to develop a monograph. The physical characterization included particle size, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and Fourier Transform Infra-red (FTIR). Metal composition and heavy metal limits were determined using Inductively Coupled Plasma Optical Emission Spectrometry (ICPOES). This study revealed the rearrangement of aragonite crystals into calcite form by grinding, trituration with aloe vera juice and incineration under controlled conditions. Moreover, the finished product was found to be devoid of organic matrix that is nacre. This study creates a foundation for the development of a master formula for commonly used Shankha Bhasma in Ayurvedic medicines.

Microstructures in relation to temperature-induced aragonite-to-calcite transformation in the marine gastropod Phorcus turbinatus.

Mollusk shells represent important archives for paleoclimatic studies aiming to reconstruct environmental conditions at high temporal resolution. However, the shells, made of calcium carbonate in the form of aragonite and /or calcite, can be altered through time which may undermine the suitability for any reconstruction based on geochemical proxies (i.e., stable isotopes, radiocarbon). At present, the diagenetic processes involved in this chemical and physical deterioration are still poorly understood. The present study aims to shed light on the onset and development of diagenetic alteration in the aragonitic shell of Phorcus turbinatus. To artificially mimic diagenesis, shells of P. turbinatus were exposed to elevated temperatures. The transformation of the mineral phase was monitored by means of Confocal Raman Microscopy whereas the structural changes were investigated using Scanning Electron Microscopy and Atomic Force Microscopy. The results indicate that the two distinct shell layers (prismatic layer and nacre) respond differently to the elevated temperatures, suggesting that the different microstructural organization and organic content may drive the onset and spread of the aragonite-to-calcite transformation. Furthermore, changes in the microstructural arrangement became visible prior to the mineralogical transition. Our results demonstrate that the specific physico-chemical characteristics of structurally different areas within the biogenic carbonates have to be taken into account when studying the phase transformation occurring during diagenesis.

Luminescence light collection technology in the aragonite of stone corals

Stone corals do not use calcium carbonate in the form of calcite, which has a calculated energy gap of 3.93 eV, but in the form of aragonite, which has a calculated energy gap of 2.88 eV (here experimentally determined to amount to 2.46 eV) as a building material. This enables the coral to harvest blue light, which is penetrating and filtering deep into the surface water of the ocean. White luminescence, which is composed of different wave lengths, is generated, and then conducted and redistributed within the aragonite structure to be supplied to the symbiotic photosynthetic algae. This mechanism of light concentration and adaptation via the aragonite structure leads to a smaller amount of light-absorbing phosphorescent pigments being required for the symbionts to survive. The resulting advantages are a significantly smaller exposure to photo-degradation, less effort for chemical synthesis and higher efficiency for solar energy conversion. The mechanism of luminescence light collection in the aragonite network is discussed on the basis of spectroscopic measurements on thin coral slices and in context with its architecture and the coral’s living activities. The relevance of the stone coral’s fractal geometry, both for broadband solar light harvesting and luminescence light collection within non-imaging optics, is emphasized. It is proposed that synthetic aragonite should be developed as a solar energy material.

Comparison of the effects of calcified green macroalga (Halimeda macroloba Decaisne) and commercial CaCO3 on the properties of composite starch foam trays

The calcified green macroalga, Halimeda macroloba, is a source of bio-based calcium carbonate which can be used as a filler in starch foam tray. In the first part of this study, the composition and structure of calcium carbonate of this species were investigated using Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD), Energy dispersive X-ray spectroscopy (EDX) and Scanning election microscopy (SEM). The morphology of the macroalgal powder particles was rod-like and organic materials (e.g. polysaccharide) and calcium carbonate (aragonite form) were present. The second part of the study investigated the effects of calcium carbonate from H. macroloba on the properties of starch foam tray and compared them with the properties of starch foam tray filled with commercial CaCO3. Interestingly, the composites starch foam trays with macroalgal powder had better impact strength than starch/commercial CaCO3 composite foam trays. Moreover, the macroalgal powder affected the thermal properties of the starch foam tray equally as well as commercial CaCO3. However, the macroalgal powder caused more significant changes in the color parameters and the whiteness values of starch foam tray than commercial CaCO3.

Coarse-grained cryogenic aragonite as end-member of mineral formation in dolomite caves

Cryogenic carbonate particles (single crystals and aggregates) have recently been recognized as important witnesses of permafrost dynamics, as they can be used to estimate the thickness and timing of development of permafrost. In this study, the petrography and geochemistry of coarse-grained cryogenic aragonite (CGCAr) identified in Zoolithen Cave in NE Bavaria, Germany, are described in detail for the first time. We provide a sequence of carbonate precipitation during freezing, where CGCAr mark the final crystallization phase in freezing water on ice. Our results support the notion that host rock composition, solution chemistry, and cave ventilation play an important role for aragonite formation in caves.Using petrographic and geochemical evidence we distinguish aragonitic spherulites, and precursory spherulitic and rhombohedral aggregates of magnesian calcite. The aragonitic particles are characterized by very low oxygen isotope (δ18O = −17.1‰ to −17.8‰) and relatively high carbon isotope values (δ13C = +1.0‰ to +0.8‰). Among the magnesian calcites the spherulitic forms show more negative oxygen and more positive carbon isotope values, compared to rhombohedral crystals (δ18O = −17.2‰ to −15.0‰ vs. −16.2‰ to −9.9‰; δ13C = +0.4‰ to −3.5‰ vs. −0.8‰ to −4.8‰). This sequence is mirrored also in mineralogical/geochemical data from the spherulitic CGCAr, where the calcite fibers show an increase in Mg from 1.5–2.5 mol-% to 7.5–10 mol-% MgCO3, before aragonitic spherulites are formed.U-series dates from cryocalcites formed prior to the identified CGCAr in Zoolithen Cave place the formation of the former into the last glacial to between 28.75 ka and 30.63 ka. Aragonitic spherulites on cryocalcites represent the end-member of the succession cold water calcite – cryocalcite – cryoaragonite. The sampling depth at 30 m below surface represents a minimum thickness of last glacial permafrost in this location in Central Europe.