The Collaborative International Dictionary of English v.0.48:

Crumbly \Crum"bly\ (-bl[y^]), a.
   Easily crumbled; friable; brittle. "The crumbly soil."
   --Hawthorne.

   Syn: crimp.
        [1913 Webster]

WordNet (r) 3.0 (2006):

crumbly
    adj 1: easily broken into small fragments or reduced to powder;
           "friable sandstone"; "friable carcinomatous tissue";
           "friable curds formed in the stomach";"crumbly cookies"
           [syn: crumbly, friable]