cleavage
1. In rocks, a tendency to split along parallel, generally closely spaced surfaces as, for example, in slate.
2. In some stone industries, the splitting along the depositional layering.
3. The rupturing of adhesive bonds between rigid materials; a prying action.
4. A tendency in some woods to split along closely spaced parallel planes, as in shingles.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.