What type of rock formations cause excessive bit wear?

• A. Hard and abrasive rock formations, such as granite, basalt, and certain types of sandstone.
• B. Soft clay formations.
• C. Sedimentary limestone.
• D. Plastic shale.

Answer: (A)

Bit wear comes from rock hardness and abrasiveness. When a drill bit cuts through rocks that are very hard and contain abrasive minerals (like quartz), the cutting surfaces are ground down quickly as they shear and grind the rock. Granite and basalt are classic examples, and some quartz-rich sandstone can be just as hard on the bit. Soft clay formations offer little resistance, limestone is softer and less abrasive, and plastic shale tends to cause other issues like sticking, not extreme wear. So the type of rock that causes excessive wear is hard and abrasive rock formations.