The usual materials engineering terms have already been defined -- most people think of "strength" as a single quantity, but there are several specific quantities that do not necessarily appear in all strong materials:
- stiffness: how much the piece deforms under stress elastically (without a permanent change)
- compressive and tensile strengths (usually most different when a
material is "strong" but not tough) -- tensile strength is often
measured to the point when the material starts to deform plastically
(permanently) or to the point when the specimen breaks entirely
- toughness (resistance to crack propagation, typically measured as the
energy required to break a notched or smooth specimen)
- hardness (resistance to deformation, typ. using a small ball as the indenter -- closely related to tensile strength, although an exact correlation depends on the material)
In addition, all of these are usually thought of as isotropic properties -- not varying in direction -- but they will depending on the material is formed. For wood, properties are highly anisotropic. Try bending a thin piece of wood with the grain and against it, for example. (One more aside: while complicated wood grains ("curly," burls, interlocked) are often prized for their beauty, woodworkers traditionally prefer to work with straight-grained stock because it's so much easier. Elm, for example, isn't often used commercially because it rarely has straight grained sections, and it's not pretty enough to be worth the effort.) Even steel and aluminum can have a "grain" -- usually the rolling direction -- and properties can differ significantly with and perpendicular to the rolling direction.
Ceramics and glasses can have high strength in compression, but even tiny flaws (almost always present) mean that they will fail in tension because they aren't tough. Once a crack has started, it takes very little energy to get bigger. They tend to make lousy tool materials as a result, although the trick of using sand or fine quartz for cutting hard materials is an excellent one -- you can cut glass with a hard grit using a copper tool because the hard grit tends to get embedded in the copper. I assume the same is true when using a cord to cut stone, although I thought that quite a bit of stone was quarried by cutting small slots and holes as stress concentrators, and wedges (or freezing water) used to split the rock at those holes or slots.
I would like to mention that "ironwood" is one of the most common names of various hard species throughout our world. It seems like just about every locale has its own ironwood.
As for cutting and shaping, most of the usual methods have been mentioned.
Traditionally, even steel tools have their problems with the tougher and harder woods, especially if you don't like sharpening them after every other cut. The simplest fix is to work the wood before it dries. You can do so much with green wood: split along the grain, form, etc. There's a great book "How to make a chair from a tree" that details these methods.
Fire and hot tools to char or degrade the iron wood (as mentioned) are also possibilities -- native Americans and other indigenous peoples use fire to hollow out trunks for boats. You could also girdle saplings (cut the living layer on the outside of the tree) to get timber for palisades -- the hard part might be the inner heartwood.
In really old times, bronze tools (and earlier bone and quartz) were often used to prepare wood, so tool hardness and strength relative to wood was even lower. The usual non-metals were used as well: silica (sand, quartz), alumina (ruby and other corundums) were most common. One that I hadn't heard of until recently was shark skin -- it makes an excellent "sandpaper" and depending on how it is prepared, can range in roughness from quite coarse to very fine. You could certainly have a local animal that incorporates silica or another hard oxide in its skin.
