bone ash

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The white, powdery calcium phosphate ash of burned bones, used as a fertilizer, in making ceramics, and in cleaning and polishing compounds.

from The Century Dictionary.

• noun Same as bone-earth.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The white, powdery ash left when bone is burnt; it is high in calcium phosphate and is used as a fertilizer and in making bone china.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun ash left when bones burn; high in calcium phosphate; used as fertilizer and in bone china