Apart from the many giant monolithic obelisks that survive in Egypt and elsewhere, there is one obelisk that is famous for its failure. The Unfinished Obelisk at Aswan would have been the largest ever erected at 42m, but it never left the quarry. This photo-essay looks at some of my images of the Unfinished Obelisk and briefly considers its significant for Egyptian archaeology.

At some time during its extraction from the Aswan granite, a large crack developed running lengthwise up the obelisk. The obelisk was abandoned, either because the stone was felt to be fatally flawed, or because the crack was too large for the masons to carve an obelisk of sufficient size to fulfill their commission.

Attempts were made to carve up the defunct obelisk to produce smaller granite items (leaving smaller, straight cracks across the obelisk at various points), but these were aborted, leaving the Unfinished Obelisk tethered to the granite.
Still bound to the living rock, the Unfinished Obelisk is a valuable source of information concerning stone quarrying and obelisk extraction. The trenches around the sides of the obelisk clearly show the use of pounders to separate the obelisk from the bedrock and these are even more visible around other partially excavated granite objects in the quarries.

It was originally thought that these trenches were cut purely by endless pounding of the bedrock, using hard stones and sand to slowly wear away the granite (Engelbach 1923), but recent research and experimental archaeology demonstrate that fire was used to weaken the granite before pounding, making it possible to extract obelisks more quickly and with fewer workmen.
The new and continuing research into stone quarrying demonstrates how valuable unfinished stone artefacts are. In its failure as an obelisk, the unfinished obelisk has found a different kind of fame amongst archaeologists and tourists, and is arguably more useful than its perfectly finished brothers and sisters. Its quarry is now a tourist attraction, with an open air museum, and it forms part of a network of important ancient stone quarries recorded around Aswan and recently studied by the Quarryscapes Project.
References
Engelbach, R. 1923. The problem of the obelisks, from a study of the unfinished obelisk at Aswan. T. F Unwin Ltd, London.
Habachi, L. 1977. The Obelisks of Egypt. New York: Charles Scribner.
Per Storemyr’s blog contains several posts of relevance to stone quarrying and obelisks and links to a recent article detailing evidence for the use of fire in hard stone quarrying.
For a general introduction to stone artefacts and stone quarrying in Egypt see also Aston B. G. Harrell, J. A and Shaw, I. 2000. Stone. In P. T Nicholson and I. Shaw (eds.) Ancient Egyptian Materials and Technology. Cambridge University Press.