An ideal piece of flaking stone lacks inclusions or weathering cracks, and exceptional pieces ring like a bell when tapped with a hammerstone. Much of the flaking debris at ancient stone sources and quarries was produced in striking off initial flakes (‘assaying’) to assess the internal quality of a potential stone and check it for cracks and flaws.

The texture of a stone is also an important criteria. Grainy stone may be isotropic, but if it is made up of large-sized grains, more energy is required to force a crack through it. Conversely, fine-grained stone requires less force to fracture. For instance, the geochemistry of granite and obsidian are similar, and both are formed from molten rock, but granite is coarse and difficult to flake whereas obsidian—a natural volcanic glass that is ideal for flaking—lacks grains entirely (it is essentially a congealed liquid).

Durability was of primary importance for some cutting tools, such as axes and adzes, as well as hammering tools such as hammerstones and mortars. In this case, stoneworkers often chose coarse-textured stones with interlocking grains, such as igneous and metamorphic rocks, because of their resistance to percussive forces. Tough stones also tend to be relatively resistant to refined flaking, so flaking was supplemented with different stone-working techniques—such as pecking and grinding—to produce these durable tools.

Abrasive stones were often selected for tools to prepare food or to manufacture other types of tools. Sandstone is the most common material used for this. Although controlled flaking is difficult in sandstone, it can be easily pecked into shape. Igneous rocks were used as abrading stones in many parts of the world.

Loose sand was often added to grinding stones used in tool manufacture, with the quartz grains enhancing the grinding stone’s abrasive qualities. Corundum grit (in its gem form, ruby and sapphire) was used as an abrasive by Egyptians to drill hard stone beads by ca. 4600 BP and by Minoans to make quartz seals ca. 3500 BP. People from the Liangzhu and Sanxingcun cultures in China were making axes using corundum abrasive by ca. 5500 BP. Later Liangzhu axes may have been polished using diamond abrasive powder by 4500 BP, and bead-makers in India were the first to use diamond chips in drilling and engraving by 2200 BP, a practice that had become widespread throughout the Roman Empire. Ancient texts suggest that Sumerians hammered corundum grit into lead sheets to create a forerunner of modern sandpaper.

Some stones have special properties that make them ideal for specific types of tools. For instance, soapstone has unique heat-retaining abilities and is easy to work by carving and abrading; it was used for stone bowls and vessels in many parts of the world. Slate separates along bedding planes into sheets, which were used until recently as roofing tiles. Marble resists flaking but responds well to pecking and grinding, and continues to be a favoured stone for sculptures. Chalcedony (agate and carnelian), jade, crystal quartz, and various gemstones are prized for their aesthetic and spiritual properties, and are ground and polished into many types of objects.

Organic materials—wood and bone—were combined with stone to make composite tools, a practice that dates to at least 70,000 years ago in South Africa. Modern stone-using people suggested to anthropologists that the organic parts of some weapon systems were more highly prized that the stone armaments because the stone parts were easily replaced.

Industrial processes analogous to metamorphism and volcanism produce stoneware ceramics and glass, and both of these materials were flaked into tools. Abrasives used in industry and cosmetics are often created artificially, and many modern gemstones and diamonds for jewellery are manufactured rather than deriving from natural sources. ‘Cremation diamonds’ are gemstones made artificially from human or pet ashes.