That would depend on which Ironwood you are talking about.
* The name Ironwood is actually a slang term given to the hardest wood of an area, region or country. There are over 80 species of wood in the world, referred to or having the word Ironwood in them.*
Probably the best way to appreciate the relative hardness of different woods is the concept of "specific gravity," a numerical scale based on 1.0 for pure water. Without getting too mathematical, the specific gravity of a substance can easily be calculated by dividing its density (in grams per cubic centimeter) by the density of pure water (one gram per cubic centimeter).
Trees With Dry (Seasoned) Wood That Sinks In Water
Olneya tesota
(Desert Ironwood): 1.15
Guaiacum officinale)
(Lignum Vitae): 1.37
Cercocarpus betuloides
Mountain Mahogany: 1.10
Diospyros ebenum)
Ebony: 1.12
Very Heavy Wood
Prunus ilicifolia
Hollyleaf Cherry: 0.98
Diospyros virginiana
Persimmon: 0.83
Quercus engelmannii
Engelmann Oak: 0.94
Carya ovata
Shagbark Hickory: 0.83
Acacia greggii
Cat's Claw Acacia: 0.85
Ostrya virginiana
Eastern Ironwood: 0.80
Quercus chrysolepis
Canyon Live Oak: 0.85
Lyonothamnus floribundus
Catalina Ironwood: 0.80
Quercus agrifolia
Coast Live Oak: 0.83
Robinia pseudoacacia
Black Locust: 0.79
Prosopis glandulosa
Mesquite: 0.77
Maclura pomifera
Osage Orange: 0.77
you will see these numbers change small amounts from one reference to another.
Trees vary from place to place and from tree to tree depending on the environment in which they have grown.