The Phi Grade Scale can be used to describe sedimentary material.
Parameter:
(1) diameter of the particle in mm
phi value =
= -LOG2(diameter in mm)
where:
• In Excel LOG2(x) is expressed as LOG(x,2)
Interpretation:
• The larger the phi value the smaller the particle. A boulder has a phi value <= -8.0 while colloid has a phi value of 12. Coarse sand has a phi value of 0.
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