Measurement of crystal size distributions

Abstract

Studies of crystal size distributions (CSD) can reveal much about how rocks solidify and under what conditions. Data from two-dimensional sections can be readily acquired at many different scales, from electron microscope images, thin sections, slabs, outcrops, and so on, but the conversion to true, three-dimensional values is complex. The widely used Wager method does not have a good theoretical basis and does not give accurate results. A modification of the Saltikov correction method is proposed here that is more accurate and can account for different crystal shapes and fabrics. Population densities determined by this method differ by factors of 0.02 to 100 from those determined by the Wager method. Published CSDs determined using other methods can be recalculated if the crystal shape and fabric parameters can be estimated. The method has been incorporated into a new program, CSDCorrections.*

Crystal size and shape distribution systematics of plagioclase and the determination of crystal residence times in the micromonzogabbros of Qisir Dagh, SE of Sabalan volcano (NW Iran)

“…through magma solidification (e.g. Cashman & Marsh 1988;Higgins 1996Higgins , 2000. Comparison of CSD curves of the mircomonzogabbros from Qisir Dagh (Fig.…”

“…To estimate the frequency of different size groups, the length and width of 2266 plagioclase grains were manually and visually measured in the longest perpendicular directions using JMicroVision software platform. Extraction of 3D shape and size distribution data from raw 2D data was done using the CSDSlice5 spreadsheet (Morgan & Jerram 2006) and CSD Corrections 1.4.0 software (Higgins 2000(Higgins , 2002. Chemical compositions of feldspars (both plagioclase and alkali feldspar) were determined with JEOL JXA-8200 electron microprobe at the California Institute of Technology, using focused electron beam (~1 micrometer in diameter), an accelerating voltage of 15 kV and a beam current of 25 nA.…”

“…Crystal population density is best represented by a plot of ln(n) versus crystal length (L). The histograms of volume fraction (number of crystals for each size) vs. size is another method for representing the CSD data (Higgins 2000;Jerram et al 2009). …”

“…The type of texture in igneous rocks depends on the rate of magma cooling and crystal nucleation, growth rates and residence time (Winkler 1949;Vernon 2004). Most of the routine textural investigation on igneous rocks deals with the description of crystal shapes, the relationship of components with each other and the relative size of crystals, all of which are often reported as qualitative data (Seasman 2000;Higgins 2000;Innocenti et al 2013). To investigate three-dimensional state of grains, Randolph & Larson (1971) proposed the Crystal Size Distribution (CSD) theory for synthetic solids, which was later developed by Marsh (1988) and applied to magmatic systems and the resultant igneous rocks.…”

Rheological controls on the eruption potential and style of an andesite volcano: A case study from Mt. Ruapehu, New Zealand

“…3). This enables us to quantify the size and abundance of each mineral phase and in some respects allows us to determine the impact of foreign crystal entrainment into the magma during ascent (i.e., using crystal size distribution analysis e.g., (Higgins, 2000(Higgins, , 2002Muir et al, 2012). In order to convert the crystal content into a volume fraction, which 230 is necessary for the rheological calculations, we use the following aspect ratios of 1:2:5 and 1:1:2 (short, intermediate, and long axes) for plagioclase and pyroxene phenocrysts respectively, and 1:1:7 for acicular pyroxene and plagioclase microlites.…”