Mechanical Properties :
Hardness triples as Zn is incorporated:
The following depicts leaf cutter ant mandibles. To the left in each picture is a young specimen's mandible and to the right is an old adult's mandible. You may notice that zinc is only found in the old adult and not in the young.
The following is the results from measurements using AFM. The mandibles were found to be as hard as a salmon tooth, and 1/5 as hard as human or chiton teeth.
Advantages over calcification?
Crustaceans employ both!
To the left in each photo below you see the Br and Zn enriched mandible and on the right you see calcified sclerite which is 8x harder.
Isopod, Porcellio scaber
The above photos represent the time elapsed results of wear resistance testing via repeated plunges into polishing grit. Notice how the harder calcefied sclerite is less resistant to wear.
Resistance to Chipping:
Below you see the before and after shots from bead-blasting of shore crab (Pachygrapsus crassipes) structures. It is clear to see which parts of the structures employ metal-halogen enrichment.
Are wear and fracture resistance more important for smaller organisms?
Large and small leaf cutter ant mandibles:
(above)Plunged in polishing grit. (below) Plunged in leaves.
