granulometric analysis particle analysis
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Particle AnalysisParticle Analysis
Granulometric AnalysisGranulometric Analysis
• Disaggregated sample passed through nested screens
• Screen intervals usually at 1 ϕ or 0.5 ϕ• Weight resting on the screens summed to
100%• Plotted as a histogram or on a probability
graph
Phi Scale, (Phi Scale, (ϕϕϕϕϕϕϕϕ))
LogLog--normal distributionnormal distribution
ϕϕϕϕϕϕϕϕ = = --loglog22(d(dmmmm))
Gaussian DistributionGaussian Distribution
•• Mean diameter (Md Mean diameter (Md ϕϕϕϕϕϕϕϕ))–– Determined graphically as the 50Determined graphically as the 50thth percentilepercentile
of the cumulative distributionof the cumulative distribution
•• Sorting (Sorting (σσσσσσσσ ϕϕϕϕϕϕϕϕ ))–– Determined graphically as the number of Determined graphically as the number of ϕϕϕϕϕϕϕϕ
classes between the 16classes between the 16thth and 84and 84thth percentilespercentiles
Gaussian DistributionGaussian Distribution Sorting ParameterSorting Parameter
Deconvolution Deconvolution of Size Dataof Size Data
• Methods of resolving data
• Use of histograms
• Sequential Fragmentation/Transport
• Interpretation of various size modes
Mount St. HelensMount St. Helens
Pyroclastic Bedded Pyroclastic Bedded deposits on deposits on StairstepsStairsteps
Changes with DistanceChanges with Distance
• Decrease in median grain size• Decrease in maximum grain size
– Pumice– Lithic clasts
• Increase in glass/crystal ratio
Component analysisComponent analysis
• Juvenile glass, pumice
• Crystals
• Lithic
Grain Shape and TextureGrain Shape and Texture
• Vesicularity– Size, abundance, shape of bubbles
• Angularity– Infers nature of magma rupture
• Rounding– Measures degree of transport
• Surface alteration– Weathering, hydrothermal, or juvenile?