Glauconite is an iron potassium phyllosilicate ( mica group) mineral of characteristic green color which is very friable and has very low weathering resistance.
59-510: It crystallizes with a monoclinic geometry. Its name is derived from the Greek glaucos ( γλαυκός ) meaning 'bluish green', referring to the common blue-green color of the mineral; its sheen ( mica glimmer) and blue-green color. Its color ranges from olive green, black green to bluish green, and yellowish on exposed surfaces due to oxidation. In the Mohs scale it has a hardness of 2, roughly
118-940: A feedstock in the synthesis of commercial fertilizer powders. In Brazil , greensand refers to a fertilizer produced from a glauconitic siltstone unit belonging to the Serra da Saudade Formation, Bambuí Group, of Neoproterozoic / Ediacaran age. The outcrops occur in the Serra da Saudade ridge, in the Alto Paranaíba region, Minas Gerais state. It is a silty-clayed sedimentary rock, laminated, bluish-green, composed of glauconite (40-80%), potassium feldspar (10-15%), quartz (10-60%), muscovite (5%) and minor quantities of biotite (2%), goethite (<1%), titanium and manganese oxides (<1%), barium phosphate and rare-earth element phosphates (<1%). Enriched levels of potash have K 2 O grades between 8 and 12%, thickness up to 50 metres (160 ft) and are associated to
177-524: A marl in an old and broad sense of that word. Thus references to "greensand marl" sometimes refer specifically to glauconite. The Glauconitic Marl formation is named after it, and there is a glauconitic sandstone formation in the Mannville Group of Western Canada . At the broadest level, glauconite is an authigenic mineral and forms exclusively in marine settings. It is commonly associated with low-oxygen conditions. Normally, glauconite
236-407: A structure known as a crystal . Some ways by which crystals form are precipitating from a solution , freezing , or more rarely deposition directly from a gas . Attributes of the resulting crystal depend largely on factors such as temperature , air pressure , cooling rate, and in the case of liquid crystals , time of fluid evaporation . Crystallization occurs in two major steps. The first
295-529: A consequence of diagenetic alteration of sedimentary deposits at the surface, bio-chemical reduction and subsequent mineralogical changes affecting iron-bearing micas such as biotite , and is also influenced by the decaying process of organic matter degraded by bacteria in marine animal shells. In these cases, the organic matter creates the reducing environment needed to form glauconite within otherwise oxygenated sediment. Glauconite deposits are commonly found in nearshore sands, open oceans and shallow seas, such as
354-423: A crystal at a high speed, sweeping away nuclei that would otherwise be incorporated into a crystal, causing the swept-away nuclei to become new crystals. Contact nucleation has been found to be the most effective and common method for nucleation. The benefits include the following: The following model, although somewhat simplified, is often used to model secondary nucleation: where Once the first small crystal,
413-428: A draft tube while outside the crystallizer there is a settling area in an annulus; in it the exhaust solution moves upwards at a very low velocity, so that large crystals settle – and return to the main circulation – while only the fines, below a given grain size are extracted and eventually destroyed by increasing or decreasing temperature, thus creating additional supersaturation. A quasi-perfect control of all parameters
472-421: A function of operating conditions with a fairly complicated mathematical process called population balance theory (using population balance equations ). Some of the important factors influencing solubility are: So one may identify two main families of crystallization processes: This division is not really clear-cut, since hybrid systems exist, where cooling is performed through evaporation , thus obtaining at
531-401: A higher propensity for containing a significant clay fraction. Although often mistaken for a shale , siltstone lacks the laminations and fissility along horizontal lines which are typical of shale. Siltstones may contain concretions . Unless the siltstone is fairly shaly, stratification is likely to be obscure and it tends to weather at oblique angles unrelated to bedding. Siltstone
590-407: A jacket around the trough. Crystals precipitate on the cold surfaces of the screw/discs, from which they are removed by scrapers and settle on the bottom of the trough. The screw, if provided, pushes the slurry towards a discharge port. A common practice is to cool the solutions by flash evaporation: when a liquid at a given T 0 temperature is transferred in a chamber at a pressure P 1 such that
649-414: A major impact on the size, number, and shape of crystals produced. As mentioned above, a crystal is formed following a well-defined pattern, or structure, dictated by forces acting at the molecular level. As a consequence, during its formation process the crystal is in an environment where the solute concentration reaches a certain critical value, before changing status. Solid formation, impossible below
SECTION 10
#1732772282866708-419: A relatively variable quality of the product along with the batch. The Swenson-Walker crystallizer is a model, specifically conceived by Swenson Co. around 1920, having a semicylindric horizontal hollow trough in which a hollow screw conveyor or some hollow discs, in which a refrigerating fluid is circulated, plunge during rotation on a longitudinal axis. The refrigerating fluid is sometimes also circulated in
767-416: A second solvent to reduce the solubility of the solute (technique known as antisolvent or drown-out), solvent layering, sublimation, changing the cation or anion, as well as other methods. The formation of a supersaturated solution does not guarantee crystal formation, and often a seed crystal or scratching the glass is required to form nucleation sites. A typical laboratory technique for crystal formation
826-546: A solution than small crystals. Also, larger crystals have a smaller surface area to volume ratio, leading to a higher purity. This higher purity is due to less retention of mother liquor which contains impurities, and a smaller loss of yield when the crystals are washed to remove the mother liquor. In special cases, for example during drug manufacturing in the pharmaceutical industry, small crystal sizes are often desired to improve drug dissolution rate and bio-availability. The theoretical crystal size distribution can be estimated as
885-507: A transformation to the equilibrium phase. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. Additionally, crystal phases can sometimes be interconverted by varying factors such as temperature, such as in
944-490: Is nucleation , the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The second step is known as crystal growth , which is the increase in the size of particles and leads to a crystal state. An important feature of this step is that loose particles form layers at the crystal's surface and lodge themselves into open inconsistencies such as pores, cracks, etc. The majority of minerals and organic molecules crystallize easily, and
1003-438: Is a clastic sedimentary rock that is composed mostly of silt . It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility . Although its permeability and porosity is relatively low, siltstone is sometimes a tight gas reservoir rock, an unconventional reservoir for natural gas that requires hydraulic fracturing for economic gas production. Siltstone
1062-453: Is a consequence of the physical characteristics of the solution, while the others define a difference between a well- and poorly designed crystallizer. The appearance and size range of a crystalline product is extremely important in crystallization. If further processing of the crystals is desired, large crystals with uniform size are important for washing, filtering, transportation, and storage, because large crystals are easier to filter out of
1121-470: Is achieved as DTF crystallizers offer superior control over crystal size and characteristics. This crystallizer, and the derivative models (Krystal, CSC, etc.) could be the ultimate solution if not for a major limitation in the evaporative capacity, due to the limited diameter of the vapor head and the relatively low external circulation not allowing large amounts of energy to be supplied to the system. Siltstone Siltstone , also known as aleurolite ,
1180-539: Is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering , crystallization occurs in a crystallizer . Crystallization is therefore related to precipitation , although the result is not amorphous or disordered, but a crystal. The crystallization process consists of two major events, nucleation and crystal growth which are driven by thermodynamic properties as well as chemical properties. Nucleation
1239-798: Is an unusual rock, in which most of the silt grains are made of quartz . The origin of quartz silt has been a topic of much research and debate. Some quartz silt likely has its origin in fine-grained foliated metamorphic rock, while much marine silt is likely biogenic, but most quartz sediments come from granitic rocks in which quartz grains are much larger than quartz silt. Highly energetic processes are required to break these grains down to silt size. Among proposed mechanism are glacial grinding; weathering in cold, tectonically active mountain ranges; normal weathering, particularly in tropical regions; and formation in hot desert environments by salt weathering. Siltstones form in relatively quiet depositional environments where fine particles can settle out of
SECTION 20
#17327722828661298-403: Is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure – note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure. The crystal growth
1357-415: Is clear that sulfate solubility quickly decreases below 32.5 °C. Assuming a saturated solution at 30 °C, by cooling it to 0 °C (note that this is possible thanks to the freezing-point depression ), the precipitation of a mass of sulfate occurs corresponding to the change in solubility from 29% (equilibrium value at 30 °C) to approximately 4.5% (at 0 °C) – actually a larger crystal mass
1416-512: Is considered a diagnostic mineral indicative of continental shelf marine depositional environments with slow rates of accumulation and gradational boundaries. For instance, it appears in Jurassic /lower Cretaceous deposits of greensand , so-called after the coloration caused by glauconite, its presence gradually lessening further landward. It can also be found in sand or clay formations, or in impure limestones and in chalk . It develops as
1475-423: Is increased using the technique of evaporation . This process is insensitive to change in temperature (as long as hydration state remains unchanged). All considerations on control of crystallization parameters are the same as for the cooling models. Most industrial crystallizers are of the evaporative type, such as the very large sodium chloride and sucrose units, whose production accounts for more than 50% of
1534-563: Is its use in Russian " icon paintings", another widespread use was for underpainting of human flesh in medieval painting. It is also found as mineral pigment in wall paintings from the ancient Roman Gaul . Glauconite, a major component of greensand , is a common source of potassium (K) in plant fertilizers and is also used to adjust soil pH . It is used for soil conditioning in both organic and non-organic farming, whether as an unprocessed material (mixed in adequate proportions) or as
1593-542: Is precipitated, since sulfate entrains hydration water, and this has the side effect of increasing the final concentration. There are limitations in the use of cooling crystallization: The simplest cooling crystallizers are tanks provided with a mixer for internal circulation, where temperature decrease is obtained by heat exchange with an intermediate fluid circulating in a jacket. These simple machines are used in batch processes, as in processing of pharmaceuticals and are prone to scaling. Batch processes normally provide
1652-493: Is the initiation of a phase change in a small region, such as the formation of a solid crystal from a liquid solution. It is a consequence of rapid local fluctuations on a molecular scale in a homogeneous phase that is in a state of metastable equilibrium. Total nucleation is the sum effect of two categories of nucleation – primary and secondary. Primary nucleation is the initial formation of a crystal where there are no other crystals present or where, if there are crystals present in
1711-476: Is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale (elevating solute concentration in a small region), that become stable under the current operating conditions. These stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by many different factors ( temperature , supersaturation , etc.). It
1770-415: Is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, and dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by K sp . Depending upon
1829-414: Is to dissolve the solid in a solution in which it is partially soluble, usually at high temperatures to obtain supersaturation. The hot mixture is then filtered to remove any insoluble impurities. The filtrate is allowed to slowly cool. Crystals that form are then filtered and washed with a solvent in which they are not soluble, but is miscible with the mother liquor . The process is then repeated to increase
Glauconite - Misplaced Pages Continue
1888-567: Is to perform a gravity settling to be able to extract (and possibly recycle separately) the (almost) clear liquid, while managing the mass flow around the crystallizer to obtain a precise slurry density elsewhere. A typical example is the DTB ( Draft Tube and Baffle ) crystallizer, an idea of Richard Chisum Bennett (a Swenson engineer and later President of Swenson) at the end of the 1950s. The DTB crystallizer (see images) has an internal circulator, typically an axial flow mixer – yellow – pushing upwards in
1947-533: The Mediterranean Sea . Glauconite remains absent in fresh-water lakes, but is noted in shelf sediments of the western Black Sea . The wide distribution of these sandy deposits was first made known by naturalists on board the fifth HMS Challenger , in the expedition of 1872–1876. Glauconite has long been used in Europe as a green pigment for artistic oil paint under the name green earth . One example
2006-419: The entropy ( S ) gain in the system by spatial randomization of the molecules has overcome the enthalpy ( H ) loss due to breaking the crystal packing forces: Regarding crystals, there are no exceptions to this rule. Similarly, when the molten crystal is cooled, the molecules will return to their crystalline form once the temperature falls beyond the turning point. This is because the thermal randomization of
2065-401: The solubility threshold at the given temperature and pressure conditions, may then take place at a concentration higher than the theoretical solubility level. The difference between the actual value of the solute concentration at the crystallization limit and the theoretical (static) solubility threshold is called supersaturation and is a fundamental factor in crystallization. Nucleation
2124-412: The wind farm industry off the coasts of Massachusetts , New York and New Jersey , glauconite-rich sands of Cretaceous to Paleogene age found in the seabed have become a hazard to the installation of monopiles used for turbine foundation. When these sands are manipulated, during the driving of monopiles, they start to crush, changing their geotechnical behaviour from sand-like to clay-like, with
2183-557: The clay and silt fraction is composed of silt-sized particles. Silt is defined as grains 2–62 μm in diameter, or 4 to 8 on the Krumbein phi (φ) scale . An alternate definition is that siltstone is any sedimentary rock containing 50% or more of silt-sized particles. Siltstones can be distinguished from claystone in the field by chewing a small sample; claystone feels smooth while siltstone feels gritty. Siltstones differ significantly from sandstones due to their smaller pores and
2242-469: The conditions are favorable, crystal formation results from simply cooling the solution. Here cooling is a relative term: austenite crystals in a steel form well above 1000 °C. An example of this crystallization process is the production of Glauber's salt , a crystalline form of sodium sulfate . In the diagram, where equilibrium temperature is on the x-axis and equilibrium concentration (as mass percent of solute in saturated solution) in y-axis , it
2301-409: The conditions, either nucleation or growth may be predominant over the other, dictating crystal size. Many compounds have the ability to crystallize with some having different crystal structures, a phenomenon called polymorphism . Certain polymorphs may be metastable , meaning that although it is not in thermodynamic equilibrium , it is kinetically stable and requires some input of energy to initiate
2360-459: The exchange surfaces. The Oslo, mentioned above, is a refining of the evaporative forced circulation crystallizer, now equipped with a large crystals settling zone to increase the retention time (usually low in the FC) and to roughly separate heavy slurry zones from clear liquid. Evaporative crystallizers tend to yield larger average crystal size and narrows the crystal size distribution curve. Whichever
2419-405: The form of the crystallizer, to achieve an effective process control it is important to control the retention time and the crystal mass, to obtain the optimum conditions in terms of crystal specific surface and the fastest possible growth. This is achieved by a separation – to put it simply – of the crystals from the liquid mass, in order to manage the two flows in a different way. The practical way
Glauconite - Misplaced Pages Continue
2478-515: The glauconitic levels, dark-green in color. Glauconite is authigenic and highly mature . The high concentration of this mineral is related to a depositional environment with a low sedimentation rate. The glauconitic siltstone has resulted from a high-level flooding event in the Bambuí Basin. The sedimentary provenance is from supracrustal felsic elements in a continental margin environment with acid magmatic arc ( foreland basin ). In
2537-457: The growing crystal. The supersaturated solute mass the original nucleus may capture in a time unit is called the growth rate expressed in kg/(m *h), and is a constant specific to the process. Growth rate is influenced by several physical factors, such as surface tension of solution, pressure , temperature , relative crystal velocity in the solution, Reynolds number , and so forth. The main values to control are therefore: The first value
2596-476: The influence of the existing microscopic crystals in the magma. More simply put, secondary nucleation is when crystal growth is initiated with contact of other existing crystals or "seeds". The first type of known secondary crystallization is attributable to fluid shear, the other due to collisions between already existing crystals with either a solid surface of the crystallizer or with other crystals themselves. Fluid-shear nucleation occurs when liquid travels across
2655-416: The last crystallization stage downstream of vacuum pans, prior to centrifugation. The massecuite enters the crystallizers at the top, and cooling water is pumped through pipes in counterflow. Another option is to obtain, at an approximately constant temperature, the precipitation of the crystals by increasing the solute concentration above the solubility threshold. To obtain this, the solute/solvent mass ratio
2714-410: The liquid saturation temperature T 1 at P 1 is lower than T 0 , the liquid will release heat according to the temperature difference and a quantity of solvent, whose total latent heat of vaporization equals the difference in enthalpy . In simple words, the liquid is cooled by evaporating a part of it. In the sugar industry, vertical cooling crystallizers are used to exhaust the molasses in
2773-427: The nucleus, forms it acts as a convergence point (if unstable due to supersaturation) for molecules of solute touching – or adjacent to – the crystal so that it increases its own dimension in successive layers. The pattern of growth resembles the rings of an onion, as shown in the picture, where each colour indicates the same mass of solute; this mass creates increasingly thin layers due to the increasing surface area of
2832-618: The purity in a technique known as recrystallization. For biological molecules in which the solvent channels continue to be present to retain the three dimensional structure intact, microbatch crystallization under oil and vapor diffusion have been the common methods. Equipment for the main industrial processes for crystallization . The crystallization process appears to violate the second principle of thermodynamics . Whereas most processes that yield more orderly results are achieved by applying heat, crystals usually form at lower temperatures – especially by supercooling . However,
2891-421: The rate of nucleation that would otherwise not be seen without the existence of these foreign particles. Homogeneous nucleation rarely occurs in practice due to the high energy necessary to begin nucleation without a solid surface to catalyze the nucleation. Primary nucleation (both homogeneous and heterogeneous) has been modeled as follows: where Secondary nucleation is the formation of nuclei attributable to
2950-426: The release of the heat of fusion during crystallization causes the entropy of the universe to increase, thus this principle remains unaltered. The molecules within a pure, perfect crystal , when heated by an external source, will become liquid. This occurs at a sharply defined temperature (different for each type of crystal). As it liquifies, the complicated architecture of the crystal collapses. Melting occurs because
3009-453: The resulting crystals are generally of good quality, i.e. without visible defects . However, larger biochemical particles, like proteins , are often difficult to crystallize. The ease with which molecules will crystallize strongly depends on the intensity of either atomic forces (in the case of mineral substances), intermolecular forces (organic and biochemical substances) or intramolecular forces (biochemical substances). Crystallization
SECTION 50
#17327722828663068-451: The risk of pile refusal, making it impossible to reach the target depth of the piles. The pile driving difficulties stem from the high frictional resistance of the native glauconite sand at the pile tip, combined with the high cohesive resistance of the altered, now clay-like material along the pile shaft. Crystallize Crystallization is the process by which solids form, where the atoms or molecules are highly organized into
3127-490: The same as gypsum . The relative specific gravity range is 2.4–2.95. It is normally found as dark green rounded concretions with the dimensions of a sand grain. It can be confused with chlorite (also of green color) or with a clay mineral . Glauconite has the chemical formula (K,Na)(Fe,Al,Mg) 2 (Si,Al) 4 O 10 (OH) 2 . Glauconite particles are one of the main components of greensand , glauconitic siltstone and glauconitic sandstone . Glauconite has been called
3186-421: The same time a concentration of the solution. A crystallization process often referred to in chemical engineering is the fractional crystallization . This is not a different process, rather a special application of one (or both) of the above. Most chemical compounds , dissolved in most solvents, show the so-called direct solubility that is, the solubility threshold increases with temperature. So, whenever
3245-448: The surroundings compensates for the loss of entropy that results from the reordering of molecules within the system. Such liquids that crystallize on cooling are the exception rather than the rule. The nature of the crystallization process is governed by both thermodynamic and kinetic factors, which can make it highly variable and difficult to control. Factors such as impurity level, mixing regime, vessel design, and cooling profile can have
3304-424: The system, they do not have any influence on the process. This can occur in two conditions. The first is homogeneous nucleation, which is nucleation that is not influenced in any way by solids. These solids include the walls of the crystallizer vessel and particles of any foreign substance. The second category, then, is heterogeneous nucleation. This occurs when solid particles of foreign substances cause an increase in
3363-442: The total world production of crystals. The most common type is the forced circulation (FC) model (see evaporator ). A pumping device (a pump or an axial flow mixer ) keeps the crystal slurry in homogeneous suspension throughout the tank, including the exchange surfaces; by controlling pump flow , control of the contact time of the crystal mass with the supersaturated solution is achieved, together with reasonable velocities at
3422-590: The transformation of anatase to rutile phases of titanium dioxide . There are many examples of natural process that involve crystallization. Geological time scale process examples include: Human time scale process examples include: Crystal formation can be divided into two types, where the first type of crystals are composed of a cation and anion, also known as a salt, such as sodium acetate . The second type of crystals are composed of uncharged species, for example menthol . Crystals can be formed by various methods, such as: cooling, evaporation, addition of
3481-419: Was prized in ancient Egypt for manufacturing statuary and cosmetic palettes . The siltstone quarried at Wadi Hammamat was a hard, fine-grained siltstone that resisted flaking and was almost ideal for such uses. There is not complete agreement on the definition of siltstone. One definition is that siltstone is mudrock ( clastic sedimentary rock containing at least 50% clay and silt) in which at least 2/3 of
#865134