Pseudomorph composition

Pseudomorphism is the change of the original chemical composition of a substance into some other equally definite compound by the action of natural agencies Pseudomorphism exists when the external crystalline form of a mineral is inconsistent with its internal chemical composition and atomic structural arrange mem. It is always a secondary process. The altered substance is known as a psetuhmiorpb. 

PSEUDOMORPH. In mineralogy and geology, a mineral, having the crystal form of one species and the chemical composition of another. Typical pseudomorphs are malachite in the form of cuprite, barite in the form of quartz, limonite in the form of pyrite. In such cases of pseudomorphism the evidence seems to be that there has been a complete chemical and molecular change but without any change of the original outward form. See also Mineralogy. 

AIN buffer layer on (0001) sapphire. Composition was determined by help of X-ray diffraction. A continuous increase of the mode energy with x was observed. An AlxGai.xN/GaN/sapphire heterostructure grown with the AIN buffer layer technique was studied in infrared reflection and Raman spectroscopy by Wetzel et al [2] (FIGURE 2). From an X-ray analysis of the c-axis an AlN-ftaction of x = 0.15 was derived. Recently, however, it was shown that AIN layers in heterostructures with GaN are coherently strained up to a thickness of at least 350 nm. This leads to misinterpretation of the AIN fraction [8], Including the deformation of the unit cell in the pseudomorphic structure above, a value 50% smaller is concluded (x = 0.08). In backscattering off the c-plane the Ai(LO) mode was determined at 752 cm 1 (square with cross symbol) in excellent agreement with the infrared reflection data [2],... 

Fossils that have been replaced with minerals are called pseudomorphs. This word means false form, referring to the specimen that has the form of one thing, but the composition of something else. Most fossil pseudomorphs are made of chalcedony (microcrystalline quartz). 

Energy-dispersive analysis of X-rays was the chosen analytical method because of its sensitivity to elements heavier than sodium, its capability of mapping elemental distribution, and its capacity for combination with a scanning electron microscope. EDS microanalysis has been reported to be suitable for the determination of mordant treatments on historical fibers (8-10) and has been used to characterize metal wrappings of combination yarns (11-13). EDS microanalysis has also been used to determine the composition of pseudomorphs and fibers in the process of mineral replacement (13, 14, 15). 

Direct fabric evidence means those forms of fabrics that are still organic and have retained their original fiber composition, and those that are partially or completely replaced by mineral compounds. Those replaced by mineral compounds, termed fabric pseudomorphs, result when fabrics in contact with metal are buried in a moist, soil environ-... 

In addition to the analysis of physical structural characteristics of textile fabric pseudomorphs, chemical information has been obtained. On bronze and copper artifacts, the pseudomorphs are composed of malachite, tenorite, and cuprite (I, 2), the formation of which probably requires moist conditions, a corrosive metal, and optimum fiber-metal contact (I). Trace elements in their structure vary from object to object and site to site (1-3), but the relationship of these elements and the fiber, metal, and soil composition is not yet known. 

Microscopic analysis of the halberd revealed a variation in color and shape of the formations on the surfaces of the blade. Green and black mineral forms are predominant, but some orange, blue, and red structures were also observed. A light-brown grainy substance fills many of the interstices between the mineral formations. The pseudomorph formations are either green or black, and the difference in their composition indicates the possibility of some chemical difference in the original organic material. This point will be discussed in a later section of this chapter. 

Pseudomorphs on a bronze Shang Dynasty halberd (ca. 1300 b.c.) were subjected to mineralogical analysis to determine their structure and composition. X-Ray diffraction, scanning electron microscopy, and energy dispersive analysis of x-rays were used in these analyses. Photomicrographs of pseudomorphs also were studied for fiber, yam, and fabric formations that give evidence of textiles. A model describing the process of silk pseudomorph formation was proposed. 

Questions that remain concerning the process of silk fabric pseudomorph formation on the bronze halberd will be resolved with further study of pseudomorphic formations, particularly on objects whose provenance is documented precisely. A more complete description of the microenvironment of the buried objects as well as a quantitative analysis of the mineral composition of the pseudomorphs is necessary for the development of equations for the chemical equilibria involved. Future work is planned to study pseudomorphs as mineralogical structures and pseudomorphs as evidence of textiles. This work includes examination of two additional Shang bronze objects currently on loan to one of the authors. 

The conditions under which a high mullite content is created are obvious from the phase diagram. The first necessary condition is a suitable composition of the system. At low temperatures (up to 1300 °C), ihe system cannot be expected to approach the state of equilibrium. When formed from kaolinite, mullite in this case frequently keeps the pseudomorphous shapes of kaolinite. The typical mullitic forms, usually needle-shaped crystals, arise only at higher temperatures. The rate of formation as we]] as the final shape of its crysta]s may be considerab]y aflected by the impurities present or by the non-clay components of the raw materia] mixture. These components also take part in the formation of the melt which is then produced in higher amounts and at lower temperatures than would correspond to the pure system A1203 —Si02. 

In the graded storm layers with abundant planktonic foraminifers microcrystalline, moderately fer-roan calcite replaced clayey/marly matrix (Fig. 6C). Some bioclasts display their original composition or show a well-preserved original shell texture, owing to pseudomorphic neomorphism to low-Mg calcite, but others are totally recrystallized/replaced by drusiform or equant mosaic calcite. Blocky calcite and syntaxial overgrowths display non-luminescent... 

The goethite pseudomorph is an easy one—the original pyrite is in the isometric system. Incidentally, these particular pseudomorphs are sometimes referred to as limonite. The term limonite is not an accepted mineral name and is used when the composition of the iron oxide is uncertain. The names of minerals are... 

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