Botanically, the term hardwood bears no relation to the hardness of a timber or tree. A hardwood is a tree that produces broad leaves and dispatches its seed in fruit. A softwood has needle like leaves and bears cones. We therefore have the contradiction that balsa is a hardwood and yew a softwood. There are two types of hardwood, deciduous, that shed their leaves in winter, and evergreens, that do not shed leaves at all. Examples of deciduous hardwoods include oak, elm, apple, and sycamore. Evergreens include mahogany, holly, balsa and eucalyptus.
Barauna is the hardest of all woods, either hardwoods or otherwise. Timber hardness is measured on the Janka scale, in pounds-force (lbf). Barauna scores 4,800 lbf meaning that it takes a force of 21.8kg. to push a steel ball 0.444 inches in diameter, halfway into the wood. Barauna is used for railway sleepers, mine timbers, piling and heavy construction joinery. It is difficult to work and cut, but it turns well. It has several other names; most commonly used are quebacho, soto and cocobalo.
Many people think that lignum vitae is the hardest wood, but it only registers 20.4kgf on the Janka scale, although it has a higher specific gravity than barauna. Used for centuries for ship's bearings because of its self-lubricating properties, resistance to water and excellent turning capabilities. Lignum vitae is now considered an endangered species, its import requiring special documentation. During the 16th. century in Europe, lignum vitae was considered to have medicinal properties, being a cure for gout and syphilis, hence its alternative name of tree of life.
Belah is another timber with a Janka rating of 20.4kgf, making it equal second in the hardness stakes. Belah is also known as black oak, although it is not an oak. The tree is native to Australia and is used for turning and firewood. Although the leaves resemble pine needles, they are long, thin leaves and should not be confused with softwood foliage.
Waddy wood, also known as acacia peuce, also has a Janka rating of 20.4kgf. This rare, endangered species is native to central Australia. Waddy is an Aboriginal word for a fighting stick, and early settlers and Aboriginals used waddy wood for tools and weapons. The timber is known to be resistant to termites and has been used for fence posts.
Mgurure has a Janka score of 201kgf. This timber, native to Kenya, is used for turning small items and in the construction of musical instruments such as chanters and drones for bagpipes. Because of its tight-grained structure, it holds musical notes well and finishes cleanly from the tool, requiring little sanding.
Janka hardness scores for more familiar hardwoods.
The hardest oak is swamp white oak, with a hardness of 73.5kgf. American beech scores 5.9kgf, and teak rates 0.454kgf. American elm and African mahogany score 376kgf and balsa rates 39.9kgf. The common yew, although a softwood, has a Janka reading of 66.7kgf.