Lithology

One of the formulas

One of the formulas

Hard

$H_{li}=\frac{100{\displaystyle \sum M}}{0.15{\displaystyle \sum M}+3.12}\pm 11.18$

$H_{li}=30M+10$

Medium hard

$H_{li}=\frac{100{\displaystyle \sum M}}{0.23{\displaystyle \sum M}+6.10}\pm 10.42$

$H_{li}=20M+10$

Weak

$H_{li}=\frac{100{\displaystyle \sum M}}{0.31{\displaystyle \sum M}+8.81}\pm 8.21$

$H_{li}=10M+10$