Dear Serge,
First, scratch the rock sample with a MOH’S hardness tool (see MOH’S scale range in our Tips section).
Then, if it measures at least 6.5, is competent, coarse grained and slightly abrasive, try a Fordia Shark 6 impregnated core bit or a T XTREME 6-9 and review its performance.
Finally, if productivity is too slow – try a softer (higher matrix such as a Shark 7. If bit performance is too low, try a harder matrix such as a Shark 4 or a T XTREME 4-6.
Enjoy drilling,
- Sam the Driller