As GPT noted, testing is the better option. I have tested sedimentary rock that I expected to fail at 4000 psi and it tested to about 8000 psi. This just shows that various formations can produce various results. Test it.
Unconfined compressive strength testing of rock provides the intact rock property. In design, you'll need the strength of the rock mass. There are tables that provide some insight to the unconfined compressive strength of intact rock types - i.e., granite, marble, claystone, shale, etc. They'll vary by a wide margin.
The influence of discontinuities, water pressure, inclination of load, etc. all temper the intact rock properties.
Hate to give you advice that leads to ruin. The geologic structure will overshadow the strength of the rock mass.
f-d, your post reminded me that Das book recommends to use 1/5 of the unconfined compressive strength for calculating pile capacities in rock, for the reasons you and others have stated above.
