We present the results from a series of jet-attrition experiments performed using a standard ASTM device (ASTM
D5757-00) on naturally occurring ash-sized (b 2 mm) pumice, a product of explosive volcanic eruption compris-
ing highly porous silicate glass. We investigate the effect of both feed grain size and attrition duration on the pro-
duction of fines. We utilize a wet methodology for fines collection to ensure recovery of the total grain size
distribution for each experimental run. The experiments convert a restricted size range of pumice particles to a
bimodal population of parent and daughter particles. The bimodal distribution develops even after short
(~ 15 min) attrition times. With increased attrition time, the volume of daughter particles increases and the
mode migrates to finer grain sizes. Jet attrition efficiency depends heavily on the particle size of the feed; our
data show little attrition for a feed of 500 μm vs. highly efficient attrition for a 250 μm feed. Our rates of attrition
for pumice are extremely high compared to rates recovered from experiments on limestone pellets. Fines pro-
duction data are well modeled by:
mfines
m0
bed
¼ 0:291 1−e−0:312t

where m0bed is the initial mass of particles in the bed, t is in hours, and the two adjustable coefficients dictate the
long time limiting behaviour (0.291) and the rate at which the limit is reached (−0.312). This functional form
provides more realistic limits in time while preserving a zero intercept and defining a plateau for long residence
times