Barry Hunt turns his focus this month on granite, the hardest of the stone groups. Once shunned by masons because of the difficulty of working it, it has been transformed by CNC machinery, diamond tooling and low price Far Eastern sources into one of the most popular stone groups.
Granite is viewed by many as the antithesis of marble, which I explored in this series last month. Granite is typically severe in appearance and is the archetype of the perception that stone is durable through the ages – with good reason, as many of the oldest stone antiquities are granite, often little changed from the day they were carved.
It might be argued that the true art of the stonemason was complete when the working of granite was mastered 4,000 years ago.
Because of its familiarity, the word granite has also entered our vocabulary as describing something immovable, enduring, hard. We talk of granite-jawed boxers, or the Duchess of York “all turned to granite, wearing solely big gems and high heels” when posing nude for a 2005 charity calendar.
Granite is probably the most widely available stone on the planet. Perversely, although it is known for its blandness, its abundance has made it probably the most diverse of stones, with thousands of varieties commercially available, some of them highly figured and decorative.
Another reason for granite’s popularity is its ability to be applied to almost any building stone use, from paving to cladding and statues to ashlar.
Furthermore, it can be highly polished and, even better, will retain the polish for many years even under extreme weathering conditions.
To the uninitiated, almost any rock of igneous (or lava) origin is called granite and little differentiation is made by the stone industry other than to call particularly dark versions ‘black granites’.
Stones such as gneiss, diorite and syenite are included in the broad trade classification, but are not what a geologist would consider truly granite and for the purposes of this article have been ignored.
The highest quality granites are recognised as those with very little variation from veining, spotting and other features. However, some of the rarer examples featuring large porphyritic and rapakivi textures are much sought after.
Quarrying and use
The recovery rate in most instances should be exceptionally high – as much as 80% – as most resources allow the cutting of neat, square or prismatic blocks using diamond wire technology.
When exposed at the Earth’s surface, granite has the potential to expand, which is the cause of granite doming and consequent curved jointing structures, although this rarely causes problems in construction as such expansion has usually already occurred prior to extraction.
Recovery rates might be reduced considerably in those resources that exploit what are effectively core stones, where the outer regions are weathered to a point where low strength is potentially problematic.
Some of the so-called “Golden Granites” from Brazil are derived from such weathered core stones.
It is not only the enduring qualities of granite that make it desirable as a building stone but also the uniform nature and potentially massive size of the blocks available because of the continental scale mode of formation of granites.
This feature was first exploited by the Egyptians with the building of their great temples and obelisks, which remain some of the largest stone monuments in history.
The temple complex of Amun-Ra at Luxor is home to the obelisk of Hatsheput, the largest standing in Egypt at 30m tall. It is said to have taken just seven months to carve from a single block of granite.
The granite used comes from Aswan, which still today contains many unfinished statues, columns, capitals and obelisks from various periods.
The Aswan granite was also used for the burial chamber of the Great Pyramid of Khufu at Giza and the lower portions of the casing stones of the other two pyramids.
An unfinished obelisk weighing more than 1,000tonnes remains in one of the quarries. It was abandoned after a crack was identified but it reveals how such great pieces of stone were produced.
The largest solid granite building in the world is the Palacio de San Lorenzo de El Escorial, 30miles outside Madrid, Spain.
This was commissioned by Phillip II of Spain in compliance with a promise to Charles V to erect a mausoleum to him and his descendants.
Following his victory at the battle of St Quentin in 1557, Phillip was finally moved to let building begin, in part to celebrate the victory and also in honour of his Patron Saint.
Juan Bautista de Toledo was the original architect between 1559 and 1563 but his untimely death allowed Juan de Herrera to take over between 1563 and 1584.
The building remains Spain’s largest and is testimony both to the construction prowess of the Spanish masons and to the properties of granite.
Examples of granite use in the UK can be found in most towns and cities, where it has been used as cladding to office buildings, in particular banks, which like to provide an impression of impregnability.
But the best examples are in Aberdeen. Here we have Marischal College, reputedly the second largest solid granite building in the world.
Aberdeen has a long history of granite production and use, which flourished in Georgian times to build a city that shimmers in the sunlight, earning it the name of the ‘Silver City’ or, more commonly, the ‘Granite City’.
The oldest structure in London is Cleopatra’s Needle, an obelisk created in 1475 BC for the Pharaoh Thothmes III and originally erected in ancient Heliopolis (North Cairo).
The needle was moved to Alexandria where it stayed for more than 1,000 years until it was given to the British in 1819.
However, it was not until 1877 that the needle was actually moved, almost being lost in the Bay of Biscay, where saving it cost six lives.
Another notable London structure is Nelson’s column by William Railton, built in 1843 using Foggintor granite from Dartmoor, which was also used for the building of the nearby Princetown Prison (granite quarrying on Dartmoor was for many years associated with convict labour).
Nelson’s column itself is said to be the largest Corinthian column in the world, rising 44m before being topped by Edmund Hodges Bailey’s 5m high effigy of Nelson. Reputedly 14 stonemasons held a dinner on top of the column before the statue was put in place. In recognition of that, a meal was served on top of the column again a few years ago when the column was renovated.
Scottish granite is still used, although in nothing like the quantities of years ago. The bulk of the cladding on the Scottish Parliamentary buildings are Kemnay granite from a quarry near Aberdeen.
Regardless of the wish to use only Scottish products, Norwegian granite was used for some of the stone cladding details.
Probably the most famous use of the Kemnay granite was for the construction of the old London Bridge that now spans an artificial lake beside Lake Havasu in western Arizona.
The children’s nursery rhyme “London Bridge is falling down” refers to the bridge that collapsed around 1014, and not the one built by John Rennie in 1831 that was sinking under its own weight into the London clay.
Legend has it that a band of Danish pirates was defending the bridge by hurling stones from it, and so the services of the Viking chieftain Olaf Haralsen were employed, his longboats being secured to the bridge and rowed to pull it and the pirates down.
Rennie’s bridge was sold in 1968 for $2.46million to the chainsaw magnate Robert Paxton McCullogh, who then spent another $5million transporting 130,000tonnes of the granite to Arizona – and that was only part of the weight of the whole bridge. The face was sawn off the stone and used to clad a concrete core that had been prepared in Arizona, while the original granite core is said to have been left in the UK, sawn into slabs, and resold as cladding.
Granite resources in the UK derive from two main areas in Scotland and South-West England, although there are also granites in Ireland (perhaps the best known coming from the Mourne mountains) and Wales.
A hundred years ago there were more than 100 quarries operating in Aberdeenshire alone.
Today, 14 granites in Scotland are listed as being in production for dimensional stone purposes. Some (Kemnay and the pink Corrennie, for example) are not actually currently being quarried, although the stone is still available because there are plenty of blocks on the ground that are being processed for the few projects that demand them from customers willing to pay the price – because granite produced in the UK is more expensive than granite imported from the Far East, where labour is less expensive and imports now dominate.
However, indigenous stone is making a come-back in the UK as customers become concerned about their carbon footprint, matching existing materials and the eight weeks or so it takes to ship stone half way round the world.
Nevertheless, low cost imported granite setts and paving has transformed many urban landscapes and, as polished slabs, has become ubiquitous as worktops in commercial and domestic kitchens.
Fitness for purpose
Of all the building stones, granite should be considered the most versatile as there are few purposes it cannot be considered fit for, while the uniformity some it displays allows it to sit well in most surroundings.
Granite can take a high polish or be given a textured finish (flamed or dolly punched, for example) that will normally be expected to last for decades, at least, and potentially centuries.
When considering the excellent physical, chemical and mechanical properties of granite, more than for any other stone, the final choice depends on aesthetics rather than build quality.
Granite is the engineer’s favourite stone group because of its high strength in all directions, low water absorption and excellent durability.