Reference Samples in Geology and Geochemistry

Abstract

The use of geologic reference samples may have started in the last quarter of the 19th century after analysts in England, Germany, and the United States deplored the large variation in data obtained by different analysts for the same constitutent in the same sample. Early samples involved in cooperative analysis, also known as “round robins,” were mainly industrial or agricultural materials of economic value, or products derived from them. Data from some round robins were so diverse that “uniformity in analysis” was a part of early committee names. The first two geologic samples of the National Bureau of Standards were analyzed cooperatively. Samples for geology and geochemistry are classified as artificial samples or as natural materials of either economic or geochemical interest—the latter distinction not always possible. Artificial samples have been prepared in several substrates, and samples in other substrates may be limited only by the ingenuity of the analyst. The principal suppliers of samples of economic interest are discussed, by country, to show the range of samples prepared by organizations. Natural samples of geochemical interest are mentioned by sample type. Because of their intended use, some geochemical samples are restricted to analysts using specific techniques. Methods used for and precautions to be observed while preparing large or small rock samples are discussed. Excess grinding of small rock samples reduces the amount of FeO found in a rock analysis. Unavoidable contamination occurs when processing rocks in steel. Tungsten carbide, and some mechanical equipment, should be avoided. A review of the allied subjects of homogeneity of a sample, sampling errors, and size of the sample grains shows that we have reinvented the wheel since 1885. Methods used tc (1) test the homogeneity of samples, (2) eliminate outliers which some scientists reject repeatedly despite warnings of statisticians, and (3) estimate best values when the method for estimating should be part of the program for a sample are discussed. Calibration lines may be used to determine if “best values” in a series of several samples are really “best” and to furnish confidence limits for a single datum. The agreement of data by an analyst for a reference sample with data preferred by an issuing organization is usually described by one of several adjectives, a subjective procedure. A variation of a x2 method may be used if a producer specifies the exact number of data for the cooperative analytical program to be furnished by each analyst and then calculates the population estimates of the mean and standard deviation for an element in a sample. Because of the large increase in the number of reference samples of all types, a revised table listing samples that may be useful in geochemistry is included. It is not known if the samples, other than those of the U.S. Geological Survey, were collected in conformance with provisions of the Plant Pest Control Regulations of the U.S. Department of Agriculture, or of similar organizations in other ...

Reference Values Following ISO Guidelines for Frequently Requested Rock Reference Materials

“…Because powdered rock RMs contain particles of different minerals, a test of sufficient homogeneity between units (Fearn and Thompson ), performed before characterisation, is required as evidence that the RM is fit for its purpose. The homogeneity tests of the investigated RMs (e.g., Flanagan , Fearn and Thompson ) were performed by their original producers or by contracted third parties (see review by Jochum and Enzweiler ). ISO Guide 34 () and ISO Guide 35 () give guidance on how to assess and implement the homogeneity testing of RMs, respectively.…”

Cd, Gd and Sm Concentrations in BCR‐1, BHVO‐1, BIR‐1, DNC‐1, MAG‐1, PCC‐1 and W‐2 by Isotope Dilution Thermal Ionisation Mass Spectrometry

“…The inherent accuracy of this method makes it a powerful procedure for establishing the levels of trace elements in geochemical reference materials (RMs). Flanagan (1986) reports: "Analysts of almost a century ago faced one problem that is still with us -the variation in data obtained by analysts determining the same constituent in presumably the same sample was unacceptably large". IDMS by thermal ionisation is seldom used for analysing RMs because the method is relatively slow and costly; however, such measurements serve a useful role by providing geochemists with accurate reference values for calibration and development purposes.…”

Representative Sampling – Another Cinderella of Particle Size Analysis

“…-rendered as coconut in Flanagan [14], fist, orange, egg, walnut, chestnut, pea, and wheat. While these appear to be units of volume, rather than mass, they are not helpful for practical purposes and a more scientific basis is required.…”

“…units (the density thus in g/cm 3 ) and all particle sizes will be in cm. We will take a particle density close to that of quartz (2.6 g/cm 3 ): Given that many instrumental techniques take around 1 -2 g of sample then the statement by Flanagan [14] that "Calculations by most methods should show that errors due to sampling heterogeneous materials may be ignored if the material is powdered to pass a 200# (75 m) sieve or, for Kleeman (1967), a 230# (63 m) sieve" can be seen to be a reasonable rule-of-thumb. It can also be seen that if the minimum mass is not taken (even if the sampling is undertaken with a rotary divider) then the required 1% precision of the measurements of the required point in the distribution cannot be met.…”

“…In 1921, the Department of the Interior, Bureau of Mines produced a useful document called "Bibliography of Literature on Sampling" [21] dealing with literature prior to that date. ("Father") Flanagan gives a good summary of the history of sampling [14] in 1986 (except that he delays the contribution of Gy to 1967 when Gy's first papers began appearing in the mid-1950's) dealing with the history to 1979 or so, and states that there are 3 major questions that sampling theories deal with:…”