[petrography] [geochemistry] geophysical logs [mineralogy] [stratigraphy]

Petrographic analyses are provided for sample splits in database table pa_measure. Analysis date, analysts, and miscellaneous data such as points counted and thin section type are provided for each split in separate tables. Analyses are reported from a list of 150 components, which are mostly phenocryst minerals but also include groundmass minerals, specific phases such as brown glass, and assemblages such as devitrified matrix. A hierarchy allows extraction of data for groups of components, such as for felsic minerals (quartz, K-spar, and plagioclase). A large variety of petrographic methods developed and applied allow the petrographer to choose within a range of higher cost effectiveness versus more accurate and complete analysis, depending on the need.

New petrographic methods described in the data base provide quantitative (modal) analysis for accessory minerals, improvements in accuracy by combining modal analysis and microprobe analysis, and comprehensive computerized documentation for analysis of size and texture for each mineral grain. Most samples used for this data base are curated and provide an extensive inventory available for additional work.

Petrographic analyses have been upgraded from rapid, less accurate analyses to more detailed analyses for several hundred samples. Superseding analyses are assigned a higher comp_qa_code (1 to 3), and superseded analyses are assigned a lower value (10 to 99, or >99 if erroneous). A comparison between these values can provide a quantitative measure of errors in petrographic analysis.

Individual mineralogical descriptions and microprobe analyses from detailed petrographic analyses are included the database. This allows detailed analysis of size and textures of component grains in each thin section, as well as relation of size and textures to chemistry from microprobe analysis.


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