Why be Grumpy in such splendid surroundings? This one's a short hike from the Silvermine East parking area with the option of including many more caches in the area. Entrance is free to this wonderful nature reserve.
Take the path marked Higher Steenberg Peak. It passes the cache Amandla and the Sleeping Dragon (worth a visit and a great coffee stop) and make your way to the waypoint at S 34° 05.479 E 018° 25.738.
Step off to the left and another 5 m to GZ - careful of fynbos, tread on the rocks please - where you'll find a small yellowish rock that will answer the grumpy question.
For the record: No rocks were hurt in making this cache. It's a home grown cement lookalike rock.
Congrats to Terunkie for another FTF and thanks for not being too grumpy about having to work with confusing coords - now updated to match the route most geocachers take.