Point counting

For other quantification, specialized graticules are available, including point counting, grids, concentric circles, and special scales. The latest methods of quantification involve automatic image analysis. 

To plot misalignment, locate the CFS or coupling on the horizontal baseline. From that point, count up or down on the vertical axis until the amount of offset is located on the mils scale. Mark this point on the graph. Use care to insure that the location is accurately located. Positive values should be above the horizontal baseline and negative values below the line. 

TOTAL VOLUME 28.00 FIRST DATA POINT COUNT 19.00... 

CALIBRATION CURVE 21 LAST DATA POINT COUNT 24.80... 

For logarithmic values, only the digits to the right of the decimal point count as significant digits. The digit to the left of the decimal point fixes the location of the decimal point of the original value. 

Plutonic rock classification by petrologic means is a simple procedure involving the use of Streckeisen ternary diagrams. Unfortunately, classification suffers from modal estimation errors involving visual estimates, or representativity issues from point counts or image analysis procedures applied to thin sections or slabs of insufficient size. 

The sampling methods illustrated in Fig. 7 are the basis of all operations in stereology and are referred to as point counting (Fig. 7A, 7B), areal analysis... 

Fig. 7. Schematic representation of four procedures commonly used to sample a field in stereo-logical analysis. These procedures have been used to study the porous structure of collagen-GAG matrices [74] and yield values for average pore diameter, pore volume fraction and other features. In this illustration, a phase A (cross-hatched) is embedded in a continuous phase B (white background). A Random point count B systematic point count C areal analysis D lineal analysis. (Reprinted from [64] with permission).

Point counting is the easiest way of determining the volume fraction of two or more phases in a microstructure. The volume fraction of a phase equals the fraction of points in an array that lies on that phase. A line count is another way of finding the volume fraction. If a series of lines are laid on a microstructure, the volume fraction of a phase equals the fraction of the total line length that lies on that phase. 

Figure 2. Color of all ingredients in the four peat types as determined by area point counts of microtome sections. (Average of three samples from each area)...

A Leitz Ortholux microscope was used to determine the maceral content of Rasa coal. The microscope was fitted with an oil- immersion 60X fluoride objective and 10X high eyepoint oculars to give an effective magnification of 720 diameters. A point count system of analysis was used for the maceral determination. 

Four points were identified per field, and a total of 1000 counts were determined for Rasa coal. This system employs a point count stage and an ocular graticule. The volume percent of macerals was calculated according to ASTM D2799-86 (14). 

Sample Separation and Characterization. Three vitrinite samples (Silkstone, High Hazels, and Westfield) were obtained by hand-picking of macroscopic vitrain bands in Carboniferous coals. Selected vitrain particles were crushed to pass a B. S. 100 mesh sieve (250 y) and polished mounts were prepared. Sample purity was determined by point-counting (sample reflectivity) 500 points, giving a + 2% (by volume) accuracy (18). 

Don t panic if time runs out. If you ve paced yourself carefully, you should have time to tackle all or most of the questions. But if you do run out of time, don t panic. Make sure that you have marked your answer sheet for all the questions that you have answered so far. Then look ahead at the questions you have not yet read. Can you answer any of them quickly, without taking the time to do lengthy calculations If you can, mark your answers in the time you have left. Every point counts ... 

It should be noted that the use of arrows (a — (3), rather than simple links, is in general necessary to ensure the correct phase ( ) of the result. Two superimposed arrows in a superposition pattern form an island, while an unlinked point counts as an O-chain. 

With any form of the internal standard method, it is necessary to employ reference standards that are as near as possible to the phases in the material as regards composition, polymorphism and degree of crystallinity. This implies both knowledge of the characteristics of the particular clinker under examination and the ability to prepare the necessary specimens, or alternatively to isolate them physically from the clinker itself. One solution (G30) has been to prepare reference patterns for a wide range of specimens of each phase and to use those that appear to correspond most closely to those present in the clinker under examination. Clinkers for which results had been obtained by point counting have also been used (K11). 

U220A14, and layer silicate-rich CS IDP U230A43. (d)-(f) Corresponding X-ray point count analyses obtained from the thin sections on a two-dimensional grid using a 200 keV electron probe with <50 nm spatial resolution at each point. Solid boxed area in (f) shows Mg-Fe-Si composition of the layer silicate and dotted boxed area shows carbonate Mg-Fe composition (source Bradley et aL, 1992). 

Figure 4 Columnar section (measured in field), petrographic composition (from point counting), and molecular weathering ratios (from major element chemical analyses) of the Sheigra paleosol (Retallack and Mindszenty, 1994) (reproduced by permission of Society for Sedimentary Geology from J. Sedim. Res., 1994, A64, 264-281).

Maceral Analyses. Maceral analyses were carried out under the microscope in reflected and fluorescent (blue-light excitation) light at magnifications of x 250 and X 500. A point-count method counting 500 points was used. This gives an accuracy of 2-3% for each maceral. 

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