hard - high
- hard
- hard ash coal
- hard bottom
- hard coal
- hard coal equivalent
- hard ground
- hard hat
- hard ore
- hard rock
- hard roof
- hard spot
- hard strata
- hard top
- hard water
- hard-caving roof
- hard-coal deposit
- hard-facing
- hard-facing alloy
- hard-metal bit
- hard-metal bit tipping
- hard-rock mechanics
- hard-rock tunneling machine
- hard-shot ground
- hard-surfacial
- hard-tempered
- hard-to-find minerals
- harden
- hardened
- hardened face
- hardened steel
- hardener
- hardening
- hardening temperature
- hardly
- hardly noticeable
- hardness
- hardness number
- hardness of the shell generator tool
- hardness scale
- hardness test
