If its a little chalky, then there's a chance it might not work for ya. It just depends how deep that chalky stuff goes. The middle part of elk antlers (where the marrow is) tends to be very porous. So, depending on how big the diameter of the porous area is and how deep the chalky area is will depend if you can make calls from it.
The short answer- cut into that sucker and see what you find!
Brian