Changes In Crystal Size Research Articles

Insights into the Sirtuin Mechanism from Ternary Complexes Containing NAD+ and Acetylated Peptide

Sirtuin proteins comprise a unique class of NAD+-dependent protein deacetylases. Although several structures of sirtuins have been determined, the mechanism by which NAD+ cleavage occurs has remained unclear. We report the structures of ternary complexes containing NAD+ and acetylated peptide bound to the bacterial sirtuin Sir2Tm and to a catalytic mutant (Sir2Tm(H116Y)). NAD+ in these structures binds in a conformation different from that seen in previous structures, exposing the alpha face of the nicotinamide ribose to the carbonyl oxygen of the acetyl lysine substrate. The NAD+ conformation is identical in both structures, suggesting that proper coenzyme orientation is not dependent on contacts with the catalytic histidine. We also present the structure of Sir2Tm(H116A) bound to deacteylated peptide and 3'-O-acetyl ADP ribose. Taken together, these structures suggest a mechanism for nicotinamide cleavage in which an invariant phenylalanine plays a central role in promoting formation of the O-alkylamidate reaction intermediate and preventing nicotinamide exchange.

Modeling Sucrose Evaporative Crystallization. Part 1. Vacuum Pan Monitoring by Mass Balance and Image Analysis Methods

Sugar boiling experiments were carried out in a pilot vacuum pan with the aim of developing new methods for monitoring and estimation of important variables in industrial crystallization. A mathematical model based on mass balances was applied, using typical on-line data recorded during the boiling runs, to determine the evolution of parameters related to the crystal content and liquor purity. In a subsequent paper (Part II), the conclusions resulting from the application of the mass balance method will be used in a study of crystal growth kinetics of sucrose in industrial and synthetic syrups. In a different approach, in situ images were captured and processed for the purpose of estimating the mean crystals size progress at the early stages of the strikeimage analysis method. A strategy is proposed to solve the problems associated with the identification of crystals in images taken directly from the suspension. The results obtained by the two methods were compared, showing good agreement both in the range of the crystal sizes and in the way crystal size changes.

Low-temperature synthesis and characterization of GaN nanocrystals from gallium trichloride precursor

Gallium nitride (GaN) has been synthesized by reacting gallium trichloride with ammonia (NH3) at low temperatures ranging from 500 to 1000 °C for 12 h. X-ray diffraction, transmission electron microscopy, infrared, and Raman backscattering spectra revealed that the synthesized GaN powder consists of single-phase nano-sized crystallites with the wurtzite-type structure. The average size of the crystals decreases with the reaction temperature from approximately ∼63 nm at 1000 °C to ∼5 nm at 500 °C. GaOCl and ϵ–Ga2O3are the intermediate products during synthesis of the GaN. Characteristic shifts of the Raman peaks are associated with the change in crystal size. The band-edge emission of GaN at 361 nm was observed on room temperature photoluminescence spectra exclusively for the sample synthesized at 1000 °C, while a new and broad emission band appeared with the center ranging from 827 to 765 nm for the samples synthesized between 500 and 800 °C.

Early diagenesis of carbonate biocrystals : isomineralogical changes in aragonite coral skeletons

Abstract Early diagenetic changes occurring in aragonite coral skeletons were characterized at the micro- and ultra-structural scales in living and fossil scleractinian colonies, the latter of Pleistocene age. The skeleton of scleractinian corals, like all biomineralized structures, is a composite material formed by the intimate association of inorganic aragonite crystallites and organic matrices. In addition to its organo-mineral duality, the scleractinian skeleton is formed by the three-dimensional arrangement of two clearly distinct basic structural features, the centers of calcification and the fibers. The latter are typically characterized by a transverse micron-scale zonation revealing their incremental growth process. The size, geometry and three-dimensional arrangement of calcification centers and fibers are taxon-specific. The earliest diagenetic modifications of these skeletons have been clearly recognized in the older parts of living colonies. The first steps of diagenesis therefore take place only a few years after the skeleton had been secreted by the living polyps, and in the same environmental conditions. Comparisons with the uppermost living parts of the coral colonies clearly show that these first diagenetic changes are driven by the biological ultrastructural characteristics of these skeletons and are conditioned by the presence of organic envelopes interbedded with and surrounding aragonite crystallites. These first diagenetic processes induce the development of thin fringes of fibrous aragonite cements growing syntaxially on the aragonitic coral fibers, an alteration of the incremental zonation of coral fibers and also preferential diagenetic changes in the calcification centers, including dissolution of their minute internal crystals. Diagenetic patterns observed in Pleistocene coral colonies typically involve the same processes already recognized in the older skeletal parts of living colonies, suggesting that diagenesis occurs through continuous processes instead of clearly differentiated stages. Selective dissolution affects calcification centers and some growth increments of coral fibers. Alteration of the initial transverse zonation of coral fibers also occur through the development of micro-inclusions clearly seen in ultra-thin sections. Although usually thicker than those observed in the ancient skeletal parts of living colonies, syntaxial aragonite cements commonly occur in these fossil skeletons. These cements are often associated with gradual textural modifications of the underlying coral fibers, in particular the loss of the transverse micron-scale zonation. This suggests that the coral skeleton forming the substratum of diagenetic cements is progressively recrystallized in secondary aragonite. This recrystallization of coral aragonite begins at the external margin of the skeleton, just below the diagenetic cements and gradually moves towards the internal skeletal parts. Recrystallization takes place through concomitant fine-scale dissolution-precipitation processes and occurs with textural changes but no mineralogical change. The process of recrystallization is likely initiated by a biological degradation of organic skeletal matrices and can be also driven by thermodynamical constraints involving the lowering of surface free energies resulting from changes in crystal size. Alteration of skeletal organic matrix, textural changes in coral biocrystals through recrystallization and precipitation of secondary diagenetic aragonite may bias the original geochemical characteristics of coral skeletons. Although more work is needed to establish the influence of these early diagenetic processes on the geochemical signatures, it is already well known that the breakdown of organic skeletal envelopes and early recrystallization of shallow-water carbonates alter the stable isotopic composition. The widespread use of coral skeletons as environmental and climatic proxies makes strongly necessary a better understanding of these early diagenetic mechanisms and a precise characterization of the fine-scale diagenetic patterns of specimens for the optimization of geochemical interpretations. In particular, it cannot be assumed that an entire aragonitic composition can guarantee that there is no or slight diagenetic alteration.

Investigation into Surface Modification of Some Polymeric Fabrics by UV/Ozone Treatment

This study evaluates the effect of uv/ozone treatments as a source of surface modifications on the properties of some polymeric fabrics. Thus, pure wool, pure polyester, and blended (wool/polyester 65/35%) fabrics are treated with uv/ozone for different time periods (1, 3, 5, 10, 15, and 20 min). The treated samples are examined and evaluated for some physical and mechanical properties, where X-ray photoelectron spectroscopy (XPS) provides evidence of the change in crystallinity/amorphousity ratio as well as the changes in crystal size. The mechanical properties measurements include tensile strength, percentage elongation, and Young's modulus values that are inversely related to a fabric's elasticity at different treatment times.

Closure in crystal size distributions (CSD), verification of CSD calculations, and the significance of CSD fans

Crystal size distribution (CSD) measurements are susceptible to the closure problem, just like chemical compositions. In its simplest form this means that the total crystal content of a rock cannot exceed 100%. Where chemical or thermal effects limit the total quantity of a single phase, closure can occur at lower volumetric phase proportions. This means that parts of the CSD diagram [ln(population density) vs. size] are not accessible. If the volumetric phase proportion is constant, then straight CSDs will appear to rotate around a point at small sizes giving a fan of CSDs. These fans are significant and do show changes in crystal sizes that can be interpreted in terms of magmatic processes. However, the correlation between the slopes (or characteristic lengths) and intercepts of individual CSDs in a family is not significant, but just a consequence of the constant phase proportion effect. Many other graphs, such as characteristic length vs. volumetric phase proportion, can give more information on magmatic processes.

Physico-mechanical and microstructural characteristics of historic and restoration mortars based on gypsum: current knowledge and perspective

Abstract The use of gypsum based mortar can be traced back over 4500 years. In Germany, in the vicinity of natural gypsum outcrops, in addition to lime mortars, calcium sulphate based mortars were widely used for joints in exterior walls of sacred buildings. There are several medieval buildings with well-preserved calcium sulphate-based mortars. The high water solubility of gypsum (CaSO 4 •2H 2 O) is a disadvantage that makes it difficult in general to handle calcium sulphate based building materials in areas exposed to weathering. Physico-mechanical as well as mineralogical investigations of historic calcium sulphate based mortars have shown that long-term weathered mortars have a much denser microstructure, larger average grain sizes, and a higher compressive strength than laboratory prepared mortars. Porosity models of these mortars will be presented which are helpful to prepare calcium sulphate based mortars with a higher water resistance for restoration purposes. The reason for the change of crystal size and morphology as well as of porosity and strength can be explained by crystallization and recrystallization processes of these calcium sulphate based mortars, as a consequence of long-term weathering. Since it is obvious that crystal size and its distribution have an enormous effect on the weathering resistance, the development of mortars with comparable structural properties is of present interest. In current use are chemical additives which modify the morphology and size of gypsum crystals of set mortars. Another possibility to influence the weathering resistance is the addition of hydraulic and/or latent hydraulic admixtures.

Parameters influencing the recrystallization rate of snow

Analysis of experimental data on snow recrystallization under various conditions shows that some components have been omitted in the presently accepted theoretical interpretations and semi-empirical models of the metamorphic process in snow. The observed recrystallization rates related to volumetric mass production, temperature gradient, and temperature are presented. An explanation of the experimental results is proposed in terms of the mass exchange inside a diffusion field of an individual cell of the ice matrix (not necessarily resulting in a crystal size increase) and the mass exchange between the diffusion fields (resulting in change in crystal size). Such interpretation can be used for a combined physical description of the equilibrium and kinetic metamorphism for different types of snow.

The role of diffusion in alkyl-benzenes catalytic cracking

The present study reports the catalytic cracking of three hydrocarbon model compounds: cumene, 1,3-di- iso-propyl-benzene (1,3-DIPB) and 1,3,5-tri- iso-propyl-benzene (1,3,5-TIPB). Experiments were developed in a novel CREC Riser Simulator, a catalytic reactor that mimics the operating conditions of large-scale fluid catalytic cracking (FCC) units. Reaction testing involved different reaction times and temperatures, using Y-zeolites of different crystal sizes (0.4 and 0.9 μm). It was shown that cumene cracking and the cumene cracking products are unaffected by the zeolite crystal size. It was proven that 1,3-DIPB cracking; it remains unaltered with changes in crystal size with however, crystal dimensions affecting product selectivities. Regarding the 1,3,5-TIPB cracking, at 350–450 °C using the 0.4 μm Y-zeolites, higher 1,3,5-TIPB conversions were obtained. Differences on 1,3,5-TIPB conversions were however, less significant at 500–550 °C. It is postulated that the 1,3,5-TIPB conversion differences are caused by constrained diffusional transport in the Y-zeolite crystals and that the increase of temperature changes the catalytic cracking of 1,3,5-TIPB from the diffusionally controlled regime to the kinetically controlled regime.

Diffusion and reactivity of gas oil in FCC catalysts

AbstractThis study considers the effects of diffusion and intrinsic catalytic reactivity for the cracking of gas oil on FCC catalysts. A four‐lump kinetic model, initially developed in a novel CREC Simulator, is employed to estimate the unconverted gas oil, the gasoline, the light gases and the coke fractions. The model incorporates a modified Thiele modulus, based on zeolite crystal properties, and an effectiveness factor. The calculated effectiveness factor is found to increase with the gas oil conversion and to decrease with the intrinsic rate constant and the zeolite crystal size. The proposed model predicts that crystal size changes in the 0.13 to 1.3 μm range affect both primary and secondary cracking reactions and the yields of gasoline, coke and light gas yields.

Illumination of vein quartz textures in a porphyry copper ore deposit using scanned cathodoluminescence: Grasberg Igneous Complex, Irian Jaya, Indonesia

Vein quartz from the Grasberg Igneous Complex in Irian Jaya, Indonesia, displays a wide range of features when observed using scanned cathodoluminescence imaging on the electron microscope. Examination of seventeen samples revealed concentric growth zoning, quartz-filled microfractures, dark luminescence near sulfides, changes in crystal size and orientation from vein edges to vein centers, turbid growth zoning, and the truncation of concentric growth zoning. Individual features observed along two large photomosaic traverses from vein margins to vein centers coupled with trace element analyses from the electron microprobe allow determination of a detailed history of fracture infilling. The two traverses indicate a simple, two-stage history of crystal growth into an open fracture followed by mechanical closing of the fracture with resulting microfractures. Electron microprobe trace-element analyses show that the Fe content of quartz reaches values of up to 4900 ppm in dark-luminescent regions near sulfide crystals and decreases smoothly to ~200 ppm along traverses away from the sulfides. The solution to the diffusion equation coupled with existing experimental data about Fe diffusion in SiO2 indicate the duration of the diffusion was perhaps on the order of thousands of years.

Solute convection during the whole process of protein crystal growth

We numerically simulated sedimentation flow and buoyancy-driven convection during protein crystal growth in which the crystal size changes from 0.1 to 100 μm and clarified how gravitational fields affect the various stages of crystal growth. When the crystal size is below a few μm, most crystals are suspended in solution and solute transport near the crystal is mainly limited by diffusive transport. When the crystal size is above a few μm, sedimentation flow dominates near the crystal, but solute transport is still mainly limited to diffusive transport. When crystals grow to several μm, most of them settle to the bottom and continue to grow there. When the size is above several 10 μm, buoyancy-driven convection dominates solute transport near growing crystals at the bottom, and the contribution from buoyancy induced convection to crystal interfacial growth rate appears on Earth in comparison with that under zero-gravity condition and increases with increasing crystal size. During the whole crystal growth process, the crystal interface growth rate shows the tendency to decrease as the crystal grows under both normal and zero-gravity conditions. Moreover, our simulations of crystal sedimentation are consistent with experimental observations of lysozyme crystallization that most crystals settle to the bottom when their size reaches several μm.

Anionic effects on the size and shape of apatite crystals grown from physiological solutions.

Comparatively little is known of the role tissue fluid electrolytes have in establishing the size and shape of apatite crystals deposited in skeletal tissues. In vitro accretion experiments using synthetic apatite seed crystals comparable in size to bone apatite were performed to assess the extent to which these crystalline features may be affected by direct electrolyte/mineral interactions. A constant composition method was used to maintain the accretion reactions under physiological-like solution conditions (1.33 mmol/liter Ca(2+), 1.0 mmol/liter total inorganic phosphate, (0 or 26) mmol/liter carbonate, 270 mmol/kg osmolality, pH 7.4, 37 degrees C). When the mass of the new accretions equaled the initial seed mass, the solids were harvested and the net change in crystal size resulting from the new accretions was assessed by X-ray diffraction line-broadening analysis. All the electrolytes examined in this study inhibited the accretion rate. The order of effectiveness was phosvitin > polyaspartate approximately polyglutamate > 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) > bovine serum albumin (BSA) > citrate. Citrate and BSA also reduced the mean crystal size of the harvested solids compared with those harvested in the absence of added electrolyte, a finding that suggests that citrate and BSA suppressed growth of the seed crystals in favor of the proliferation of new smaller crystals. In contrast, a net increase in size following accretion compared with controls suggests that the other more strongly inhibiting electrolytes stimulated growth of the primary seed crystals and/or of the secondary crystals. These size changes, however, were anisotropic, with the anions effecting primarily increases in crystal width/thickness rather than in length. The effects were also more pronounced in the presence of carbonate. Our findings suggest that the strength of the interaction with the crystal surface may be relatively more important than molecular size or conformational complexity in establishing the effect that electrolytes have on apatite growth and proliferation. The results also suggest that adsorbed electrolytes may be a significant factor in controlling the size of apatite crystals in skeletal tissues by inducing proliferation of new crystals and/or affecting crystal shape by selectively modifying growth of the lateral dimensions.

Chemical and Isotopic Constraints for Recrystallization of Sedimentary Dolomites from the Western Canada Sedimentary Basin

Mississippian shoal carbonates of Western CanadaSedimentary Basin are important hydrocarbon hosts.Dolomitization plays a major role in the evolution ofreservoir porosity in these carbonates. This processvaries across the basin and reflects, in part, divergentsources and chemistry of pore fluids. Dolomites fromseveral petroleum reservoirs were analyzed formineralogical, geochemical and isotopic variation. Thedata clearly demonstrate the progressive and complexrecrystallization of dolomite during shallow and deepburial in modified marine, meteoric and burial fluids.These data include: change in crystal size,stoichiometry, cathodoluminscence characteristics,stable oxygen and carbon isotopic shifts and changesin radiogenic Sr isotopic composition. However,regional geology, tectonic history and fluid flowevolution play important roles in the diageneticimprints and the degree of recrystallization. Early microcrystalline dolomite formed in normalmarine and evaporative conditions in Mississippiancarbonates from Western Canada Sedimentary Basinhave undergone variable degrees of recrystallization, frompristine dolomite akin to Holocene sabkha dolomitewith preserved mineralogical and chemical attributesto highly recrystallized mesodolomite, however stillnonstoichiometric, but with highly altered chemicalsignatures. Careful attention should be made to localgeology, hydrodynamics and fluid flow when investigatingdolomite recrystallization in sedimentary basins.

Texture and strength changes of buried surface-hoar layers with implications for dry snow-slab avalanche release

AbstractBuried layers of surface hoar are the failure plane for many slab avalanches, including fatal human-triggered avalanches in various mountain regions. These layers may persist as weak layers in the snow cover for weeks or months. It is therefore essential for operational avalanche forecasters to monitor the evolution of persistent weak layers, such as buried surface hoar. Traditional grain-shape observations of isolated grains with a magnifier and crystal screen do not show bonding that is decisive for strength. In this study we used in situ microphotography and observations of texture to complement strength measurements from shear frame tests. Buried layers of surface hoar consist of crystals most of which extend from the layer below to the layer above, and may exhibit a columnar or truss-like structure. Observations and measurements show that texture and crystal size change little over periods of up to several months during which the snowpack remains dry. Under these conditions, layer thickness decreases while density and strength increase. Based on field measurements, we argue that the increase in strength is primarily due to penetration of the surface-hoar crystals into the adjacent layers, especially at the bottom of the buried surface-hoar layer, where bonding is critical. The weak bonding at the bottom implies that shear failure occurs at the lower interface rather than within the weak layer. On slopes, we find that surface-hoar crystals that were initially surface-normal are tilted downslope faster than predicted by published shear strain rates for settled snow, indicating that shear strain is concentrated in these layers. The characteristic texture of buried surface hoar (columnar or truss-like) permits collapsing at the time of fracture. The gravitational energy released by the displacement of the slab may contribute to the extensive fracture propagation associated with buried surface-hoar layers.

Supraphysiologic levels of testosterone affect cancellous and cortical bone in the young female cynomolgus monkey.

The goal of this study was to evaluate the effects of chronically-elevated male levels of the potent androgen testosterone on the quality and quantity of both cancellous and cortical bone in a young (mean age 8.0 years), nonhuman female primate model (M. fascicularis). Thirteen intact female monkeys received continuous testosterone supplementation via subcutaneous implants over a 24-month period. A group of 16 untreated, intact, age-matched female monkeys served as controls. At sacrifice, the lumbar vertebrae and femora were recovered in order to analyze the bone mineral quality and quantity of cancellous and cortical bone, respectively, and compared to the control group. Mineralization profiles of the vertebrae and femora were obtained using the density fractionation technique. Chemical analysis of the three largest fractions retrieved by density fractionation was performed to evaluate differences in %Ca, %P, Ca/P ratio, and mineral content (%Ca + %PO4) between the control and experimental groups. In addition, unfractionated bone powder was examined by X-ray diffraction to identify any changes in crystal size. Coronal sections of vertebrae were analyzed for structural parameters using histomorphometry and image analysis. Cross sections taken at the midshaft diaphyseal femora were analyzed for structural macroscopic and intracortical parameters. A nonsignificant shift in the mineralization profile of the vertebrae was observed whereas there was a significant shift in the mineralization profile towards more dense bone in the treated femora as compared with controls (P < 0.05). There was no difference in terms of size/strain of the cortical or cancellous bone crystal as detected by X-ray diffraction. There was a trend towards an increase in cancellous bone area (B.Ar.) in the testosterone-treated vertebrae (P = 0.08) as compared with controls. The architecture of the cancellous bone remained nonsignificantly different between the treatment and control groups as evaluated by image analysis. There was a decrease in osteoid perimeter (P = 0.05) in the experimental group as compared with controls. There was a significant decrease in eroded perimeter measurements in the experimental group as compared with controls (P < 0.03). Although there was a trend towards an increase in cancellous bone area, mineralization was not significantly different in the vertebrae of testosterone-treated female monkeys, indicating that the newly-formed bone tissue became relatively normally mineralized over the two-year period. An increase in bone area, with indices of an overall decreased remodelling pattern as compared with controls, suggests that cancellous bone in the young, nonhuman female primate had been receptive to supraphysiologic levels of testosterone supplementation over the two-year period. There was a trend for an increase in cortical bone area and width with an increased periosteal perimeter in the testosterone-treated group as compare with controls. There was an increase in intracortical remodelling activity with a significant increase in percent porosity (P < 0.05), osteonal bone (P < 0.05), and mean wall width (P < 0.05) in the testosterone-treated group. In conclusion, the cancellous bone from female monkeys appeared to respond to the antiresorptive stimulus of male levels of testosterone with significantly diminished turnover parameters in this compartment. In contrast, the cortical bone compartment responded by displaying significant intracortical remodelling over a two-year period.

Three‐dimensional observations of ice crystal characteristics in polar ice sheets

In ice core studies, mean crystal size is generally measured on a section image of an ice specimen. However, an ice crystal with a complex shape may appear as several cells on a section image; consequently, the mean crystal size may be underestimated by overcounting the crystals on the image. We examined this phenomenon, which we called duplication effect, through three‐dimensional observation of crystal shapes. In terms of results, we found that the frequency in which duplicate cells appear on a section image is linear with respect to the frequency of which randomly drawn lines on the image pass a cell more than once. On the basis of this empirical relationship, the error on the mean crystal size caused by the duplication effect can be revised from the section image itself. As to its application, we examined crystal sizes in some Antarctic ice specimens and found that the extent of change of crystal size steadily increased with depth up to 100 m and then fluctuated between 6% and 10% in the deeper parts.

Surfactant promoted crystal growth of micronized methylprednisolone in trichloromonofluoromethane

The effect of drug concentration and particle size, as well as surfactant type and composition, on the apparent solubilities and crystal growth of methylprednisolone (MP) in trichloromonofluoromethane (CFC-11) was examined. Apparent solubilities of micronized MP in CFC-11 were consistently greater than those of the unmicromized drug. Although the micronized and unmicronized drug were the same polymorph (form I), micronized MP was higher in amorphous content. Despite the existence of apparent sypersaturation, micronized MP suspended in CFC-11 in the absence of surfactant showed no crystal growth over a 120 day period. Lipophilic surfactants showed differing abilities to solubilize MP in CFC-11. High concentrations of sorbitan trioleate (Span 85; 10 −2 M) increased the apparent solubility of micronized MP 3-fold. This resulted in net growth (increasing volume median diameter, Dvm) of drug suspended at concentrations ≤ 0.01% by weight. Oleic acid and lower concentrations of Span 85 solubilized drug to lesser extents and failed to promote detectable growth. Greater suspension concentrations of drugs (≥ 0.03% w/w) also showed negligible changes i9n Dvm, even when formulated with 10 −2 M Span 85. Preformulation of drugs in metered dose inhalers (MDIs) should include crystal size measurements in propellant-surfactant blends as functions of time. In some cases, changes in crystal size may be avoided by appropriate selection of surfactant, surfactant concentration and drug concentration in suspension.

Thermal conductivity of Zn doped CoFe2O4ferrites

Abstract A series of samples of the type Co1-xZnxFe2O4 (x = 0.0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0) was prepared as ceramics. The existence of a single phase was confirmed by x-ray studies. The thermal conductivity and specific heat were measured at temperatures ranging from 100°C to 200°C. The thermal conductivity had a minimum value at x = 0.4, caused by maximum scattering of thermal phonons which arose from the change of crystal size and excess of lattice vacancies. The phonon frequency was estimated to have an optimum value at x = 0.4, resulting from maximum porosity which disturbs the propagation of the thermal waves.

Relationship between plagioclase crystallization and cooling rate in basaltic melts

Rock textures commonly preserve a record of the near-surface crystallization history of volcanic rocks. Under conditions of simple cooling without convection or mixing, textures will reflect sample cooling rate, the temperature at which crystallization was initiated, and the distribution of mineral phase precipitation across the crystallization interval. Compilation of plagioclase size and number density data on natural (dike, sill and lava lake) and experimental samples suggests that (1) growth and nucleation rates of plagioclase in natural basaltic samples are a predictable function of cooling rate, and (2) the observed crystallization rate dependence on cooling rate is similar to that observed in experiments initiated at subliquidus temperatures. Comparison of natural and experimental samples thus suggests that most basalts crystallize under conditions of heterogeneous nucleation, with the number density of preexisting nucleii partially controlling textural responses to cooling rate changes. Time scales of crystallization and cooling in magmatic systems are intimately linked through a balance between heat removal from the system and heat evolved through crystallization. Evaluation of textural data in the context of recent numerical models of crystallization in simple (one- and two-component systems) provides new insight into regularities in the crystallization behavior of basaltic magmas. For example, the rate of change in crystal size (and number density, as dictated by mass balance) has been used as a measure of the relative importance of time scales of crystallization and cooling in numerical models of crystallizing systems. In natural samples, plagioclase size scales with the length scale of cooling such that a logarithmic plot of grain size as a function of normalized distance across the dike has a slope that appears approximately independent of dike width (solidification time). Comparison with available textural data for other phenocryst phases suggests that the same may be true for pyroxene and magnetite crystallization, with each phase having a characteristic slope probably controlled by the thermodynamic properties of the crystallizing phase. Measured crystal size distributions are unimodal and show maximum frequencies in the smaller size classes; distributions broaden and the grain size at peak frequency increases with increasing crystallization times (decreasing cooling rates). In contrast, partially crystallized Makaopuhi lava lake samples have crystal size distributions that decrease exponentially with increasing crystal size. Measured size distributions in dikes can be explained by late stage modification of Makaopuhi-type distributions through loss of small crystals, possibly the consequence of growth without nucleation. Finally, this compilation of the textural response of basaltic magmas to changes in cooling rate suggests that empirical calibrations of crystallization rate dependence on cooling rate from natural samples provide a reasonable model for plagioclase crystallization in near-surface basaltic systems. Predicted growth rates will be slow and relatively constant (10-10–10-11 cm/s) for crystallization times expected in most shallow volcanic systems (<1000 years).