scholarly journals Preparation of Thin Sections

1998 ◽  
Vol 6 (7) ◽  
pp. 8-9
Author(s):  
Ian Chaplin

The optical examination of a rock sample in thin section is the quickest and most economical method for classifying rock type and determining which analytical route to follow.Thin sections for transmitted light are the most common, but there are also:Polished Thin Sections • Polished sections are used for classification and identification of minerals that cannot be determined in standard thin sections. They are also essential for microprobe analysis. Minute mineral grains are analyzed by bombarding them with a focused bean of electrons, which generate x-rays, characteristic of the elements within the grains. X-rays are identified and quantified to determine the chemical composition of minerals.

Author(s):  
D. E. Johnson ◽  
M. Isaacson

Electron microprobe analysis has been used increasingly in, recent years for low Z analysis of thin biological sections. Although this technique has produced useful results, the sensitivity is limited by two main factors. First, the fluorescence yield (wK) decreases rapidly with decreasing Z. Using the value of wK (for carbon for example, only about one out of every 400 K ionizations in carbon results in a carbon x-ray. Second, this poor x-ray production efficiency is coupled with the inherently poor x-ray collection efficiency of most microprobe detectors. In thin sections the x-rays are emitted uniformly over 4TT steradians but the detector subtends only a small solid angle at the specimen. Hall estimates the collection efficiency of most diffracting detectors at 10−4 and, with the qualification of much lower peak to background ratios, he estimates the collection efficiency of solid state nondiffractive detectors as 10−4 to 10−2.


Author(s):  
Corina Ionescu ◽  
Volker Höck

Electron microprobe analysis (EMPA) provides information on the chemical composition of minerals and their relationships in archaeological ceramics by utilizing a narrow electron beam to stimulate the emission of X-rays. Among various signals produced, the most important are the back-scattered electrons (BSE), the secondary electrons (SE) and the characteristic X-rays. The possibility to combine BSE images, SE images, elemental mapping and quantitative analysis offers a sound basis for integrated interpretation of the ancient ceramics. The precise compositional and fabric features resulted by EMPA are indicators of the raw materials and their provenance. Even when in small amounts, the composition of the newly formed phases enables narrowing down the technological constraints, such as firing temperature and atmosphere.


Author(s):  
C.W. Akey ◽  
M. Szalay ◽  
S.J. Edelstein

Three methods of obtaining 20 Å resolution in sectioned protein crystals have recently been described. They include tannic acid fixation, low temperature embedding and grid sectioning. To be useful for 3-dimensional reconstruction thin sections must possess suitable resolution, structural fidelity and a known contrast. Tannic acid fixation appears to satisfy the above criteria based on studies of crystals of Pseudomonas cytochrome oxidase, orthorhombic beef liver catalase and beef heart F1-ATPase. In order to develop methods with general applicability, we have concentrated our efforts on a trigonal modification of catalase which routinely demonstrated a resolution of 40 Å. The catalase system is particularly useful since a comparison with the structure recently solved with x-rays will permit evaluation of the accuracy of 3-D reconstructions of sectioned crystals.Initially, we re-evaluated the packing of trigonal catalase crystals studied by Longley. Images of the (001) plane are of particular interest since they give a projection down the 31-screw axis in space group P3121. Images obtained by the method of Longley or by tannic acid fixation are negatively contrasted since control experiments with orthorhombic catalase plates yield negatively stained specimens with conditions used for the larger trigonal crystals.


2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110198
Author(s):  
Feng Yin ◽  
Deqiu Dai

The new Cuban chondrite, Viñales, fell on February first, 2019 at Pinar del Rio, northwest of Cuba (22°37′10″N, 83°44′34″W). A total of about 50–100 kg of the meteorite were collected and the masses of individual samples are in a range 2–1100 g. Two polished thin sections were studied by optical microscope, Raman spectroscopy and electron microprobe analysis in this study. The meteorite mainly consists of olivine (Fa24.6), low-Ca pyroxene (Fs20.5), and troilite and Fe-Ni metal, with minor amounts of feldspar (Ab82.4-84.7). Three poorly metamorphosed porphyritic olivine-pyroxene and barred olivine chondrules are observed. The homogeneous chemical compositions and petrographic textures indicate that Viñales is a L6 chondrite. The Viñales has fresh black fusion crust with layered structure, indicating it experienced a high temperature of ∼1650°C during atmospheric entry. Black shock melt veins with width of 100–600 μm are pervasive in the Viñales and olivine, bronzite, and metal phases are dominate minerals of the shock melt vein. The shock features of major silicate minerals suggest a shock stage S3, partly S4, and the shock pressure could be >10 GPa.


2020 ◽  
Vol 4 (1) ◽  
pp. 13-18
Author(s):  
E. J. Oziegbe ◽  
V. O. Olarewaju ◽  
O. O. Ocan

Samples of mafic intrusive rock were analyzed for their mineralogical and chemical properties. The textural relationship was studied using the petrographic microscope, elemental composition of minerals was determined using the Electron Microprobe and the whole rock chemical analysis was done using the XRF and ICP-MS. The following minerals were observed in order of abundance; pyroxene, amphibole, plagioclase, biotite, opaque minerals, quartz and chlorite, with apatite and zircon occurring as accessory mineral. Two types of pyroxenes were observed; orthopyroxene (hypersthene) and clinopyroxene. Texturally, amphiboles have inclusions of plagioclase and pyroxene. The plagioclase has undergone sericitization. The chemical composition of the pyroxene is En51.95Fs44.53Wo3.52, biotite has Fe/(Fe+Mg):0.42, Mg/(Fe+Mg):0.59, and plagioclase is Ab63.5An34.55Or1.95. Whole rock chemistry shows a chemical composition; SiO2: 45.15 %, Al2O3: 14.04 %, Fe2O3: 16.01 %, MgO: 5.65 %, CaO: 7.58 % and TiO2: 3.59 %. There is an enrichment of LREE and a depletion of HREE. Based on the minerals, mineral chemistry and the geochemistry of the studied rock, the rock is mafic and hydrous minerals formed by hydration recrystallization of pyroxene. The rock has extensively retrogressed but has not been affected by any form of deformation.


Author(s):  
Lucile-Morgane Hays ◽  
Adeline Kerner

Digitization and online publishing of museum specimen data are happening worldwide. Studies based solely on online data become increasingly accessible. The current events, for example, reducing our transport-related carbon footprint or the COVID-19 pandemic, provide key opportunities to highlight the full value of digitized collections and their related tools, which allow us to continue our research from home or at least without travelling. Are existing data resources and tools adequate for engaging in a research project from beginning to end? To address this issue, we propose to use the Mexican archaeocyaths digitized collection from the Museum National d’Histoire Naturelle, Paris, France (MNHN) and the freeware Annotate in order to describe and identify all the archaeocyaths from the Mexican Cambrian reef. Archaeocyaths are aspiculate sponges that lived during the Cambrian Period. They were the first animals to build reefs. In the MNHN collection, they are found as thin-sections with several archaeocyaths per thin-section (Fig. 1). Multiple individuals are grouped under a single collection number and a single species name. The list of species in the thin-section is only captured on the paper label, and cannot currently be found online. To study an archaeocyaths' reef, the archaeocyaths have to be described and identified one by one, and the location of each specimen has to be accuratly captured. Is it possible to do this with Annotate? Can a palaeontologist use only digitized specimens and Annotate to study a complete fauna of a given time and space? Annotate is an image annotation tool for the natural sciences. It allows users to measure, count, and tag all the morphological structures of an organism. Photos may be imported from the Recolnat database or users may import their own photos. Users can measure lengths, surfaces, and angles, count occurrences and add points of interest. Users can also tag the different individuals to identify them. Morphological terms may be imported as a standardized list from Xper2 or Xper3. Xper3 is a web platform that manages descriptive data and provides interactive identification keys. The results of the measurements and annotations can be exported into CSV format (comma-separated values) or into a structured descriptive data (SDD) format. To identify an archaeocyath to genus level, we need to identify morphological structures and count the occurrence of some of them, and for an identification to the species level, we need to measure different additional parts. The standardized list of morphological terms has been imported from the archaeocyaths genera knowledge base and the list of measurements has been created directly in Annotate. Lengths (e.g., pore size, cup diameter), counts (e.g., number of septae, number of pores) and points of interest (e.g., tumuli, canals, septa) are easy to use. What are the key lessons learnt to remember at the end of this study? The digitized archaeocyaths from Mexico have been identified as easily with Annotate as if a microscope and thin sections were used. The CSV export provided quick access to statistics calculations. The main difference between a microscope and Annotate is the working time. Some functionalities of Annotate are not optimized, their uses are time consuming. For instance, the importation of photos is not really appropriate for archaeocyaths studies. Two sections (transversal and longitudinal) per specimen are necessary to see all the morphological structures. These two parts of the same rock are packed together with one collection number. While users can easily switch from one section to another with a microscope, they can not with Annotate. Annotate allows only one photo per collection number from Recolnat, but not images of the two sections and their metadata. The main difference between a microscope and Annotate is the working time. Some functionalities of Annotate are not optimized, their uses are time consuming. For instance, the importation of photos is not really appropriate for archaeocyaths studies. Two sections (transversal and longitudinal) per specimen are necessary to see all the morphological structures. These two parts of the same rock are packed together with one collection number. While users can easily switch from one section to another with a microscope, they can not with Annotate. Annotate allows only one photo per collection number from Recolnat, but not images of the two sections and their metadata. Although Annotate is not an intuitive tool to use it is still very powerful however, some training is required to fully take advantage of it, and there is no documentation available. This freeware has great potential as it can assist researchers in their work and proposes an alternative to the need to travel around the world to study a fossil.


1970 ◽  
Vol 14 ◽  
pp. 15-20
Author(s):  
Naresh Kazi Tamrakar ◽  
Lalu Prasad Paudel

Quality of aggregate is of extreme concern when it is to be used for infrastructures. Besides, many physical and mechanicalproperties of the aggregate, presence or absence of deleterious constituents and alkali-silica reactivity are especially importantwhen aggregates are to be used in concrete structures. High potential of alkali-silica reactivity or alkali-carbonate reactivity andpresence of deleterious constituents may impair the infrastructures.A ledge rock sample from the heap to be taken for crushing was petrographically analysed for alkali-silica reactivity. Inoverall, two rock clans (dolosparstone and dolomicrosparstone) with three sub clans (rock type X, Y and Z) from the sample 2 areidentified. Rock type X (dolosparstone) constitutes 82.94% of the whole sample, and shows notable amount of quartz and calciteveins, and carbonaceous material and hematite on the mosaic of dolospars. Rock types Y (dolosparstone) and Z (dolomicrosparstone)contain trace amount of microquartz, mega quartz (>15 mm) and carbonaceous opaques. The rock type Z is dominantly composedof dolomicrospars. Major portions of all the rock types are characterised by mosaics of dolomite in association with variableamounts of muscovite, quartz, and calcite. Calcite often replaces the mosaics of dolomite and bands of quartz, forming a veinnetworks in rock types X and Y. Silica is represented by a low-temperature mega quartz either in ground or in veins, a trace amountof microquartz in rock types Y and Z. There is no other reactive silica components, thus showing a low potential to alkali-silicareactivity. However, the sample shows potential of alkali-carbonate reactivity as significant proportion of rock type havingdolomicrospars are found.DOI: http://dx.doi.org/10.3126/bdg.v14i0.5433Bulletin of the Department of Geology Vol.14 2011, pp.15-20


2021 ◽  
Vol 15 ◽  
Author(s):  
Ronald S. Petralia ◽  
Ya-Xian Wang

The post-embedding immunogold (PI) technique for immunolabeling of neuronal tissues utilizing standard thin-section transmission electron microscopy (TEM) continues to be a prime method for understanding the functional localization of key proteins in neuronal function. Its main advantages over other immunolabeling methods for thin-section TEM are (1) fairly accurate and quantifiable localization of proteins in cells; (2) double-labeling of sections using two gold particle sizes; and (3) the ability to perform multiple labeling for different proteins by using adjacent sections. Here we first review in detail a common method for PI of neuronal tissues. This method has two major parts. First, we describe the freeze-substitution embedding method: cryoprotected tissue is frozen in liquid propane via plunge-freezing, and is placed in a freeze-substitution instrument in which the tissue is embedded in Lowicryl at low temperatures. We highlight important aspects of freeze-substitution embedding. Then we outline how thin sections of embedded tissue on grids are labeled with a primary antibody and a secondary gold particle-conjugated antibody, and the particular problems encountered in TEM of PI-labeled sections. In the Discussion, we compare our method both to earlier PI methods and to more recent PI methods used by other laboratories. We also compare TEM immunolabeling using PI vs. various pre-embedding immunolabeling methods, especially relating to neuronal tissue.


1991 ◽  
Vol 05 (21) ◽  
pp. 1447-1456 ◽  
Author(s):  
A. R. HARUTUNYAN ◽  
L. S. GRIGORYAN ◽  
A. S. KUZANYAN ◽  
A. A. KUZNETSOV ◽  
A. A. TERENTIEV ◽  
...  

Two samples of benzene-treated Bi–Pb–Sr–Ca–Cu–O powder exhibited at 300 K magnetic field dependent diamagnetism and magnetization irreversibility. The treatment with benzene resulted also in the appearance of microwave absorption at low magnetic fields, while is sensitive to magnetic history of the sample. From X-ray diffraction data one can see that upon benzene treatment the reflections of 85 K and 110 K phases do not change practically, but a series of new reflections appeared, indicating a lattice modulation with 4.9 nm periodicity. A microprobe analysis revealed substantial inhomogeneity of chemical composition across the samples. The room temperature anomalies were weakened in one sample and vanished in the second upon thermal cycling.


2021 ◽  
Author(s):  
Hesham Talaat Shebl ◽  
Mohamed Ali Al Tamimi ◽  
Douglas Alexander Boyd ◽  
Hani Abdulla Nehaid

Abstract Simulation Engineers and Geomodelers rely on reservoir rock geological descriptions to help identify baffles, barriers and pathways to fluid flow critical to accurate reservoir performance predictions. Part of the reservoir modelling process involves Petrographers laboriously describing rock thin sections to interpret the depositional environment and diagenetic processes controlling rock quality, which along with pressure differences, controls fluid movement and influences ultimate oil recovery. Supervised Machine Learning and a rock fabric labelled data set was used to train a neural net to recognize Modified Durham classification reservoir rock thin section images and their individual components (fossils and pore types) plus predict rock quality. The image recognition program's accuracy was tested on an unseen thin section image database.


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