The majority of the mineral phase of the Lytechinus variegatus tooth is comprised of magnesium containing calcite crystal elements, collectively arranged so that they appear as a single
crystal under polarized light, as well as under X-ray or electron irradiation. However, the crystal elements are small, and
in spite of the common alignment of their crystal axes, are not the same size or shape in different parts of the tooth. The
toughness of the tooth structure arises from the fact that it is a composite in which the crystals are coated with surface
layers of organic matter that probably act to inhibit crack formation and elongation. In the growth region the organic components
represent a greater part of the tooth structure. In the most heavily mineralized adoral region the primary plates fuse with
inter-plate pillars. Using Scanning Electron Microscopy; TOF-SIMS mapping of the characteristic amino acids of the mineral
related proteins; and isolation and characterization of the mineral-protected protein we report that the late-forming inter-plate
pillars had more than a three-fold greater Mg content than the primary plates. Furthermore, the aspartic acid content of the
mineralrelated protein was highest in the high Mg pillars whereas the mineral-protected protein of the primary plates was
richer in glutamic acid content.These results suggest that the Asp-rich protein(s) is important for formation of the late
developing inter-plate pillars that fuse the primary plates and increase the stiffness of the most mature tooth segment. Supported
by NIDCR Grant DE R01-01374 to AV. 相似文献
Calcium carbonate crystals with various morphologies have been found in a variety of biospecimens and artificially synthesized structures. Usually, the diversity in morphology can be attributed to different types of interactions between the specific crystal faces and the environment or the templates used for the growth of CaCO3 crystals. On the other hand, isotropic amorphous calcium carbonate (ACC) has been recognized as the precursor of other crystalline calcium carbonate forms for both in vivo and in vitro systems. However, here we propose a self-confined amorphous template process leading to the anisotropic growth of single-crystalline calcite nanowires. Initiated by the assembly of precipitated nanoparticles, the calcite nanowires grew via the continuous precipitation of partly crystallized ACC nanodroplets onto their tips. Then, the crystalline domains in the tip, which were generated from the partly crystallized nanodroplets, coalesced in the interior of the nanowire to form a single-crystalline core. The ACC domains were left outside and spontaneously formed a protective shell to retard the precipitation of CaCO3 onto the side surface of the nanowire and thus guided the highly anisotropic growth of nanowires as a template.
The ways are considered for increasing the efficiency of luminescent separation of many types of mineral raw material due to the presence of calcite in them. The versatility of luminescent method for mineral raw material separation is shown by studying apatite-calcite ore beneficiation. 相似文献
This paper assesses the diagenetic history of potential fluvial hydrocarbon reservoir rocks deposited within incised valley systems of the Lower Carboniferous Marar Formation in western Libya. Outcrop data were collected in the Tinedhan Anticline, located at the southern margin of the Ghadames Basin. Four discrete intervals with channelized sandstones were identified in a section dominated by alternating offshore mudstones and shallow-marine clastics. The incised channels were cut during major sea-level lowstands, and filled by fluvial sandstone packages up to 50 m thick. Fifty-eight samples from four different localities, representing three lowstand systems tracts, were analysed to obtain a statistically meaningful mineralogical and compositional dataset. In addition to burial compaction, three main diagenetic events influenced the reservoir quality of the sandstones. Firstly, early eodiagenesis involved kaolinitization of plagioclase grains. This began before subsequent calcite cementation, probably as a result of flushing by meteoric pore-waters. The deformation of kaolinite during later compaction resulted in the formation of pseudomatrix which further reduced porosity and permeability. Kaolinite is commonly transformed to illite at temperatures above 140°C in the presence of K-feldspar. Although K-feldspar was recorded in the samples, no illite was observed, suggesting that the Lower Carboniferous strata in the study area were not buried in excess of approximately 3.5 km. The second diagenetic phase was the precipitation of calcite cement, present either dispersed throughout the sandbodies or as concretions up to 2 m across, in both cases reducing reservoir quality. The high intergranular volumes (IGV) of calcite-cemented sandstones (ranging between 35% and 40%) suggest that cementation occurred at burial depths of <500 m. Sandstones without calcite cement have lower IGV of between 17% and 25% as a result of mechanical and chemical compaction. Stable C and O isotope analysis of the calcite cement also supports precipitation at shallow burial depths, indicating a meteoric pore-water source for the calcite. The third and final diagenetic stage was partial chloritisation of kaolinite during meso-diagenesis. The elevated temperatures required for this transformation indicate burial to a minimum depth of approximately 2.5 km, which is consistent with the compaction data. Despite these diagenetic effects, the fluvial sandstones have an average porosity of 12%, with a range from 0.5% up to 25%. Permeability measurements on four sandstone samples indicate that the development of pseudomatrix did not reduce permeability significantly. 相似文献
In the conventional kiln, mega-crystalline calcite (m-CC) breaks apart easily during calcinations, and cannot be easily converted to CaO due to that it requiring a lot of heat. In this study, m-CC was calcined to CaO of around 1 mm using the rotary microwave kiln. Furthermore, CaCO3 was produced by the carbonation process and hydrothermal process, and the form of CaCO3 was characterized.Calcination of m-CC using the rotary microwave kiln resulted in CaO (97 wt%) of relatively fine size.CaCO3 of colloidal-shaped and 6 μm in size could be prepared by applying the carbonation process to Ca(OH)2 using a bubble reactor at 25 °C. As the carbonation temperature increased from 25 to 80 °C, the shape of prepared CaCO3 changed from a colloidal-type to spindle-type of 1 μm due to self-assembly. Also, hexagonal-shaped aragonite could be prepared by the hydrothermal process with the supersaturated Ca(HCO3)2 solutions. 相似文献
Aqueous carbonation of Ca(OH)2 is a complex process that produces calcite with scalenohedral calcite phases and characterized by inadequate carbonate species for effective carbonation due to the poor dissolution of CO2 in water. Consequently, we report a solid-liquid-gas carbonation system with an ionic liquid (IL), 1-butyl-3-methylimidazolium bromide, in view of enhancing the reaction of CO2 with Ca(OH)2. The use of the IL increased the solubility of CO2 in the aqueous environment and enhanced the transport of the reactive species (Ca2+ and CO32−) and products. The presence of the IL also avoided the formation of the CaCO3 protective and passivation layer and ensured high carbonation yields, as well as the production of stoichiometric rhombohedral calcite phases in a short time. 相似文献