The 18 studied rocks can be categorized into 5 groups based on their
relative reduction in PL strength.Group 1 (sample 1–9)comprises resistant intrusive igneous rocks that exhibit generally similar strength
values(Table 3) regardless of whether samples were recovered from active or inactive surfaces. These data demonstrate the importance of lithology on aggregate strength, particularly as a function of its control
on resistance to weathering. Group 2 (samples 10 and 11) includes intrusive micaceous igneous rocks. Micas are common igneous mineral
and they have well developed cleavage. Cleavage planes allow the
water to penetrate into the rock, which, when exposed to freeze–thaw
action, causes the rock to break into thin layers.