The mechanism of impact attrition of sodium carbonate monohydrate crys
tals has been elucidated by recording the impact event using a high-sp
eed image converter camera. It was -found that the attrition mechanism
depended on the impact velocity and on particle orientation on impact
. For impacts on sharp corners and edges, particle damage appeared to
result from semi-brittle failure at all velocities tested. For impacts
on crystal faces, however, a threshold velocity was identified, above
which brittle fracture occurred, and below which no visible damage wa
s detected. The impact attrition rate was measured as a function of nu
mber of impacts and particle size for an impact velocity below the thr
eshold identified. The attrition rates were initially high, but as the
number of impact cycles increased the rate decreased to a constant va
lue. These steady-state attrition rates are shown to be directly propo
rtional to the original particle size. This trend supports a semi-theo
retical model for the prediction of attrition rates using fracture mec
hanics.