New Insights on the Diurnal Mechanism of Calcification in the Stony Coral, Stylophora pistillata

Scleractinian corals are evolutionary-successful calcifying marine organisms, which utilize an endo-symbiotic relationship with photosynthetic dinoflagellate algae that supply energy products to their coral hosts. This energy further supports a higher calcification rate during the day in a process known as light enhanced calcification. Although this process has been studied for decades, the mechanisms behind it are still unknown. However, photosynthesis and respiration also cause daily fluctuations in oxygen and pH levels, resulting in the coral facing highly variable conditions. Here we correlated gene expression patterns with the physiological differences along the diel cycle to provide new insights on the daily dynamic processes, including circadian rhythm, calcification, symbiosis, cellular arrangement, metabolism, and energy budget. During daytime, when solar radiation levels are highest, we observed increased calcification rate combined with an extensive up-regulation of genes associated with reactive oxygen species, redox, metabolism, ion transporters, skeletal organic matrix, and mineral formation. During the night, we observed a vast shift toward up-regulation of genes associated with cilia movement, tissue development, cellular movement, antioxidants, protein synthesis, and skeletal organic matrix formation. Our results suggest that light enhanced calcification is related to several processes that occur across the diel cycle; during nighttime, tissue might elevate away from the skeleton, extending the calcifying space area to enable the formation of a new organic framework template. During daytime, the combination of synthesis of acid-rich proteins and a greater flux of ions to the sites of calcification facilitate the conditions for extensive mineral growth.

Uniaxial Hydroxyapatite Growth on a Self-Assembled Protein Scaffold

Biomineralization is a crucial process whereby organisms produce mineralized tissues such as teeth for mastication, bones for support, and shells for protection. Mineralized tissues are composed of hierarchically organized hydroxyapatite crystals, with a limited capacity to regenerate when demineralized or damaged past a critical size. Thus, the development of protein-based materials that act as artificial scaffolds to guide hydroxyapatite growth is an attractive goal both for the design of ordered nanomaterials and for tissue regeneration. In particular, amelogenin, which is the main protein that scaffolds the hierarchical organization of hydroxyapatite crystals in enamel, amelogenin recombinamers, and amelogenin-derived peptide scaffolds have all been investigated for in vitro mineral growth. Here, we describe uniaxial hydroxyapatite growth on a nanoengineered amelogenin scaffold in combination with amelotin, a mineral promoting protein present during enamel formation. This bio-inspired approach for hydroxyapatite growth may inform the molecular mechanism of hydroxyapatite formation in vitro as well as possible mechanisms at play during mineralized tissue formation.

Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

The Martabe deposits in Sumatra, Indonesia formed in a shallow crustal epithermal environment (200–350 °C) associated with mafic intrusions, usually recognised in domes, adjacent to an active right-lateral wrench system. Ten samples containing alunite were collected for high-resolution geochronology, to determine if overprinting fluid systems could be recognised by dating alunite separates. The heating time for each step was chosen to ensure reasonable uniformity in terms of the incremental percentage of 39Ar gas release during each of many steps, allowing age spectra to be analysed using the method of asymptotes and limits. Several distinct growth events could be recognised. In addition, each sample was subjected to ultra-high-vacuum (UHV) furnace step-heating, and 39Ar diffusion experiments conducted at the same time as 40Ar/39Ar geochronology, to determine the argon retentivity of the mineral grains being analysed. The heating schedule ensured Arrhenius data uniformly populated the inverse temperature axis, with sufficient detail to allow the application of the Fundamental Asymmetry Principle (FAP) during analysis of the Arrhenius spectrum. Results show activation energies between 370–660 kJ/mol. Application of Dodson’s recursion determines that closure temperatures would range from 400–560 °C for a cooling rate of 20 °C/Ma, which is higher than any possible temperature to be expected in the natural system. This gives confidence that the ages represent growth during periods of active fluid movement and alteration, since the deposit formed at temperatures < 200 °C at a depth of < 2 km. We conclude that gold in the Purnama pit was the result of fluid rock interactions during very short-lived mineral growth episodes at ~ 2.25 and ~2.00 Ma.

Crystalline stenonian time features from earth and beyond

The writings of Niels Stensen (Steno) on mineral growth and modification in his Prodromus, together with his work on time and process in other solids, are here synthesized as five classes of time features defined by changes in the visible continuity of either or both chemistry and orientation. This organization highlights Steno’s implicit recognition of the fractal, scale-invariant nature of natural time features with regard to space, time, and material. The effectiveness and validity of this Stenonian geochronology framework is demonstrated down to atom scale with modern case studies of the U-Pb geochronology mineral zircon from samples originating from the Earth, Moon, and Mars and spanning most of solar system history. Recently discovered nano-scale features, here termed chronostructures, were intimated by Steno in his corpuscular view of mineral behaviour. The remarkable advances in the Prodromus are seen here as a resulting from the intersection of Steno’s highly attuned approach to visual perception, his adoption of Stoic (Senecan) ethics early in his career to guide his natural philosophy, and the influence of the Galilean scientific environment of Florence. It is shown that, by virtue of its scale-invariant and intensive properties, Stenonian geochronology continues to serve as an independent and critical check on the accuracy of absolute geochronology measurements of geologic time given the latter’s inherent dependence on sample volume and the assumption of the chemically closed system. In this way Steno’s scientific legacy continues to help propel human understanding of how we see our place in time.

Fluid and Solid Inclusions in Host Minerals of Permian Pegmatites from Koralpe (Austria): Deciphering the Permian Fluid Evolution during Pegmatite Formation

Fluid inclusions (FIs) and associated solids in host minerals garnet, tourmaline, spodumene, and quartz from six pegmatite fields of Permian origin at Koralpe (Eastern Alps) have been investigated. Although pegmatites suffered intense Eoalpine high-pressure metamorphic overprint during the Cretaceous period, the studied samples originate from rock sections with well-preserved Permian magmatic textures. Magmatic low-saline aqueous FIs in garnet domains entrapped as part of an unmixed fluid together with primary N2-bearing FIs that originate from a host rock-derived CO2-N2 dominated high-grade metamorphic fluid. This CO2-N2 fluid is entrapped as primary FIs in garnet, tourmaline, and quartz. During host mineral crystallization, fluid mixing between the magmatic and the metamorphic fluid at the solvus formed CO2-N2-H2O–rich FIs of various compositional degrees that are preserved as pseudo-secondary inclusions in tourmaline, quartz, and as primary inclusions in spodumene. Intense fluid modification processes by in-situ host mineral–fluid reactions formed a high amount of crystal-rich inclusions in spodumene but also in garnet. The distribution of different types of FIs enables a chronology of pegmatite host mineral growth (garnet-tourmaline/quartz-spodumene) and their fluid chemistry is considered as having exsolved from the pegmatite parent melt together with the metamorphic fluid from the pegmatite host rocks. Minimum conditions for pegmatite crystallization of ca. 4.5–5.5 kbar at 650–750 °C have been constrained by primary FIs in tourmaline that, unlike to FIs in garnet, quartz, and spodumene, have not been affected by post-entrapment modifications. Late high-saline aqueous FIs, only preserved in the recrystallized quartz matrix, are related to a post-pegmatite stage during Cretaceous Eoalpine metamorphism.

Insights from elastic thermobarometry into exhumation of high-pressure metamorphic rocks from Syros, Greece

Retrograde metamorphic rocks provide key insights into the pressure–temperature (P–T) evolution of exhumed material, and resultant P–T constraints have direct implications for the mechanical and thermal conditions of subduction interfaces. However, constraining P–T conditions of retrograde metamorphic rocks has historically been challenging and has resulted in debate about the conditions experienced by these rocks. In this work, we combine elastic thermobarometry with oxygen isotope thermometry to quantify the P–T evolution of retrograde metamorphic rocks of the Cycladic Blueschist Unit (CBU), an exhumed subduction complex exposed on Syros, Greece. We employ quartz-in-garnet and quartz-in-epidote barometry to constrain pressures of garnet and epidote growth near peak subduction conditions and during exhumation, respectively. Oxygen isotope thermometry of quartz and calcite within boudin necks was used to estimate temperatures during exhumation and to refine pressure estimates. Three distinct pressure groups are related to different metamorphic events and fabrics: high-pressure garnet growth at ∼1.4–1.7 GPa between 500–550 ∘C, retrograde epidote growth at ∼1.3–1.5 GPa between 400–500 ∘C, and a second stage of retrograde epidote growth at ∼1.0 GPa and 400 ∘C. These results are consistent with different stages of deformation inferred from field and microstructural observations, recording prograde subduction to blueschist–eclogite facies and subsequent retrogression under blueschist–greenschist facies conditions. Our new results indicate that the CBU experienced cooling during decompression after reaching maximum high-pressure–low-temperature conditions. These P–T conditions and structural observations are consistent with exhumation and cooling within the subduction channel in proximity to the refrigerating subducting plate, prior to Miocene core-complex formation. This study also illustrates the potential of using elastic thermobarometry in combination with structural and microstructural constraints, to better understand the P–T-deformation conditions of retrograde mineral growth in high-pressure–low-temperature (HP/LT) metamorphic terranes.

Mechanisms of Enamel Mineralization Guided by Amelogenin Nanoribbons

The nanofibrous nature and its intricate structural organization are the basis for the extraordinary ability of sound enamel to outlive masticatory forces at minimal failure rates. Apatite nanofibers of several hundreds of micrometers to possibly millimeters in length originate during the secretory stage of amelogenesis as 2-nm-thin and 15-nm-wide ribbons that develop and grow in length under the guidance of a dynamic mixture of specialized proteins, the developing enamel matrix (DEM). A critical role in the unidirectional and oriented growth of enamel mineral ribbons has been attributed to amelogenin, the major constituent of the DEM. This review elaborates on recent studies on the ability of ribbon-like assemblies of amelogenin to template the formation of an amorphous calcium phosphate precursor that transforms into apatite mineral ribbons similar to the ones observed in developing enamel. A mechanistic model of the biological processes that drive biomineralization in enamel is presented in the context of a comparative analysis of enamel mouse models and earlier structural data of the DEM emphasizing a regulatory role of the matrix metalloproteinase 20 in mineral deposition and the involvement of a process-directing agent for the templated mineral growth directed by amelogenin nanoribbons.

Crystallization via non-classical pathways: Nanoscale imaging of mineral surfaces

&lt;p&gt;The advancement in analytical imaging techniques, including atomic force microscopy (AFM) and scanning and transmission electron microscopies (SEM and TEM), has allowed us to observe processes occurring at mineral surfaces in situ at a nanoscale in real space and time and hence giving the possibility to elucidate reaction mechanisms. Classical crystal growth theories have been established for well over 100 years and while they can still be applied to explain crystal growth in many growth scenarios, we now know that these models are not always an accurate description of the mechanism of all crystal/mineral growth processes, especially where nanoparticle formation is observed. Consequently there is a current challenge at the forefront of understanding crystal/mineral growth mechanisms. This work describes experimental observations of non-classical crystallization processes at the nanoscale. Using AFM as well as SEM and TEM imaging, we demonstrate that many minerals commonly grow by the attachment of nanoparticles on an existing mineral surface, often resulting from the coupling of dissolution of a parent phase and the precipitation of a new product mineral. Through varied examples of crystal/mineral growth, including calcite and other carbonates, barite, brucite, and apatite, we define the importance of the mineral-fluid interface and the aqueous fluid interfacial (boundary) layer in the control of crystal growth. Whether a crystal will grow by classical monomer attachment resulting in step advancement or by the formation, aggregation and merging of nanoparticles, will be controlled by the aqueous fluid composition at the mineral-fluid interface. The processes described also allow for the development of porosity within the new mineral and hence have important consequences for fluid movement and element mobility within the Earth. Additionally an understanding of natural mineral growth has implications for geomimetic applications for the manufacture of functional engineered materials.&lt;/p&gt;

On the constitutive equations for coupled chemical reaction and deformation of porous rocks

&lt;p&gt;Deformation, chemical reactions, and fluid flow in the geological materials are coupled processes. While some reactions are thought to be a consequence of fluid assisted dissolution on the stressed mineral surfaces and precipitation on the free surface, other reactions are caused by mineral replacement wherein a less stable mineral phase is replaced by a more stable phase, involving a change in solid volume and build-up of stresses on grain contacts, also known as a force of crystallization. Most of the existing models of chemical reactions coupled with fluid transport either assume dissolution-precipitation process or mineral growth in rocks. However, dissolution-precipitation models used together with fluid flow modelling predict a very limited extent of reaction hampered by pore clogging and blocking of reactive surfaces, which will stop reaction progress due to the limited supply of fluid to reactive surfaces. Yet, field observations report that natural rocks can undergo 100% hydration/carbonation. Mineral growth models, on the other hand, preserve solid volume but do not consider its feedback on porosity evolution. In addition, they predict the unrealistically high force of crystallization on the order of several GPa that must be developed in minerals during the reaction. Here, using a combination of effective media theory and irreversible thermodynamics approaches, we propose a new model for reaction-driven mineral expansion, which preserves porosity and limits unrealistically high build-up of the force of crystallization by allowing inelastic failure processes at the pore scale. To fully account for the coupling between reaction, deformation, and fluid flow we derive macroscopic poroviscoelastic stress-strain constitute laws, that account for chemical alteration and viscoleastic deformation of porous rocks. These constitutive equations are then used to simulate the reactive transport in porous rocks.&lt;/p&gt;