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Major and trace element contents of andesite, AMH-1, and dunite, DTS-2, were determined by computerized semiquantitative spectrographic analysis. Analysis of variance shows no significant difference for between bottle and within bottle variances at the 95% confidence level so the two rock samples may be accepted as homogeneous for all elements determined by this method. Estimates of the averages and of the standard deviations for bottles and for error are included in the tables along with the data obtained with the computer. A single preliminary analysis of AGV-2, in preparation as a replacement for AGV-1, is also reported. Established USGS rock standards, AGV-1 and DTS-1, were used as quality control samples for the characterization of AMH-1 and DTS-2. INTRODUCTION Supplies of USGS standards for geochemical investigations are being continually exhausted. Thus, the search for replacement standards is an ongoing concern. The sources of the rocks from which the andesite, AMH-1, and the dunite, DTS-2, were prepared are given below. Andesite, AMH-1, was collected from a volcanic flow exposed at a parking lot at Timber-line Lodge, south side of Mt. Hood at Long 121° 42' 30" W, Lat 45° 19' 19" N. This is a pyroxene andesite. Andesite, AGV-1, was also from Oregon but was collected about 250 miles SSE of AMH-1. Andesite, AGV-2, was collected from the same site as AGV-1. Dunite, DTS-2, was collected in the Twin Sisters location in Oregon, Long 121° 58' W, Lat 48° 45'. This is the same location from where DTS-1 was collected. ANALYTICAL TECHNIQUE The processing of these samples followed the procedure previously described (Flanagan, 1967). An important part of the procedure consisted of randomly selecting three bottles, one from each third of the total batch of prepared sample. Two portions from each of the three bottles for each different rock sample were randomly analyzed. The analytical data were then re-ordered to evaluate the analysis of variance. AGV-1 and DTS-1 were analyzed at the same time to allow direct comparison of elements in a standard USGS andesite and a standard USGS dunite. AGV-2 was analyzed in a separate sample sequence. The computerized analysis of spectrographic data from photographed optical emission spectra is routine. The basic recorder system (Helz et al., 1969) and computer program (Walthall, 1974) have been described, but a 4-by20-in photographic plate is now used in place of the two 4-by-10-in plates. Refinement of the computer program by Catharine P. Thomas (1975) resolved problems of spectral-line interferences. Duplicate 15-mg portions from each of the three randomly selected bottles of each of the rocks were mixed with 30 mg of graphite. After the electrodes were loaded, the 12 sampler, were arced and analyzed in random order. The samples were arced in a 70% argon-30% oxygen atmosphere under carefully controlled conditions as described by Dorrzapf (1973). After the plates were developed (Dorrzapf, 1973) the spectra were recorded and analyzed as previously described (Helz and others, 1969). The basis of the system is a scanning microphotometer. The optical system follows conventional practices for good resolution, high contrast, and low scattered or diffused light detection. The optics are designed to sample a portion of the spectrum 1 mm high by 7 /urn wide (about a quarter of the width of a spectral line). Light passing through the plate is detected by a solid state detector and then is sampled by an analog-to-digital (A/D) converter. The heart of the signal processing system is a 2100S Hewlett-Packard (H-P) minicomputer with 32K of memory. Within 5 minutes after recording the last sample, the requested number of two-page report forms containing the concentrations of 64 elements for as many as 10 samples on each report form are printed on the H-P 2607A line printer. Information about effective arc temperature and electron pressure during each arcing and the calculated total oxides (considering only major constituents) for each sample also are available (Golightly et al., 1977). The computer algorithm calculates the coefficients of first and second degree polynomials for the analytical curve of In intensity vs. In concentration. It evaluates the curve for range, goodness of fit, and slope. It suggests a working concentration range for the line such that a lower limit defined by a signal/noise ratio of 2 is maintained (Walthall, 1974). Each photoplate contains spectra from several standard reference materials in addition to spectra from a suite of samples and an iron two-step calibration spectrum. The standard reference materials are selected from 20 well-characterized rocks chosen to represent the variety of materials analyzed. The analyst selects rock standards that are compositionally similar to the samples described by the individual requesting the analyses. The computer program recognizes these rock standards and compares the results calculated for Si, Al, Fe, Ca, Mg, Ti, Co, Pb, and Zr with accepted values in Any use of tradenames or trademarks is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey. these standards. These nine elements were chosen because they include major rock constituents and have a wide range in volatility, thus enabling checks for loss of refractory elements if a molten bead pops from the anode during the arcing procedure. The analyst makes an evaluation of the analytical usefulness of the line on the basis of its profile, intensity, and location. The data can be automatically entered into the wavelength table. On the basis of the tabulated data from standard reference materials interferences can be identified so that line priorities and concentration ranges can be adjusted to circumvent errors. Generalized interference treatments are of two types: subtraction or line changing. The subtraction routine allows gross corrections by subtracting an equivalent concentration contributed by the interfering line. This subtraction uses prestored coefficients, relating the concentration of interference to apparent concentration of analyte, all of which have been predetermined in the absence of the analyte. The matrix of DTS-2 has created an unresolved interference for Li and neither can V and Zn values be determined because of the high concentrations of Cr and Ni. The symbol "H" is reported in cases of unresolved interferences. RESULTS AND DISCUSSION Analyses of elements by this method are presently not as accurate as analyses by wet chemical or X-ray fluorescence methods, but the method represents a significant improvement over visual determinations. The data obtained are semiquantitative for several reasons. Standards used are similar to synthetic standards of Myers and others (1961) that were made to approximate the "average" silicate rock. Six-step concentrations of these standards are arced on separate plates. Prestored coefficients of the analytical curves obtained from the arcing of these standards are used to compute the concentrations of samples arced and recorded later (Thomas, 1979; Walthall, 1974). Since arcing conditions are not exactly reproducible between plates, well-characterized USGS standard rocks are analyzed on the same plate as the samples. For quantitative data, standards need to be arced on each plate and calibration coefficients based on those standards are determined for each plate individually. Tables 1 and 2 contain data for elements in AMH-1 and DTS-2. For AMH-1, 35 elements were at concentrations below the detection limit for that element, which is reported as a "less than" in the table. There were 43 elements with concentrations below the detection limit in DTS-2. Computations for the analysis of variance were performed for the data, except where one or more observations were missing or where reported as less than a lower limit. The estimates of the mean and the standard deviation for bottles and for errors and the conclusions regarding homogeneity from the F tests resulting from the calculations are included in the tables. Tables 3 and 4 provide semiquantitative data for USGS standards AGV-1 and DTS-1 and for AGV-2, which is also being prepared for use as a pyroxene andesite standard. The data for AGV-1 and DTS-1 are well within the recommended values for these rocks. DTS-2 appears to be very similar to DTS-1. Chromium is the only element of a significantly different concentration. It was found to be greater by a factor of 3 in DTS-2 than in DTS-1. AMH-1 appears to be more similar to AGV-1 than AGV-2 might be. Only elements barium, chromium, lead, and zirconium are greater in AGV-1 by a factor of 3 than in AMH-1. However, sodium, titanium, niobium, silver, lanthanum, yttrium, ytterbium, lead, and zirconium appear to be significantly different between AGV-1 and AGV-2. With continued study of AGV-2, these differences will become more conclusive. CONCLUSIONS Negative values for the estimates of within bottle variances may be attributed to sample fluctuations about an average of zero. However, negative values preclude calculation of an F ratio. When the variation due to bottles randomly selected from the three thirds is not significant, the sample is declared to be homogeneous for that element. AMH-1 and DTS-2 are homogeneous for all elements where F ratio could be calculated. DTS-2 appears to be very similar to DTS-1 and promises to be a good replacement for it. It appears AMH-1 would be a better choice than AGV-2 for replacement of AVG-1. REFERENCES CITED Dorrzapf, A.F., Jr., 1973, Spectrochemical Computer Analysis Argon Oxygen d-c Arc Method for Silicate Rocks: U.S. Geological Survey Journal of Research, v. 1, No. 5, p. 559-562. Flanagan, F.J., 1967, U.S. Geological Survey Silicate Rock Standards: Geochimica et Cosmochimia Acta, v. 31, p. 289-308. Golightly, D.W., Dorrzapf, A.F., Jr., and Thomas, C.P., 1977, Sets of Spectral Lines for Spectrographic Thermometry and Manometry in D.C. Arcs of Geologi

Computerized spectrographic data for two new USGS rocks, AMH-1 and DTS-2