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Building, paving and roofing stone: Geology and mineral planning factsheets for Scotland

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Natural stone is the principal construction material of Scotland's pre-1919 building stock and its use can be traced over a period of 5000 years from the early dry-stone constructions of Caithness and the Northern Isles. Traditionally, locally sourced stone was used so that the varied geology of Scotland has had a profound influence on the nation's cultural identity and built heritage. Stone was used for a wide variety of construction purposes including strategically important medieval defences (castles, towers, walls), simple dwellings and farms. From the 16 th century onwards there was a burgeoning requirement for stone to supply villages, towns and cities. This demand for stone reached a peak during 19 th century with the expansion of Scottish cities with their extensive tenement developments. Stone was also supplied for lighthouses, harbours and bridge construction. At the same time Scottish stone, particularly granite and flagstone was exported to the continent, the eastern seaboard of America and beyond. At the height of production in the 1850s stone was supplied from over 700 quarries across Scotland. Improvements in transport, dwindling local supplies and architectural choice encouraged the importation of stone, especially sandstone, from northern England from the end of the 19 th century. From this peak of activity in the indigenous stone industry, the rapid decline in use of stone, accompanied by a decline in knowledge and skills to work and use this material, occurred during the early decades in the 20 th century as cheaper manufactured materials including brick and concrete were introduced. However, recent decades have witnessed renewed activity as the demand has increased for repair, maintenance and conservation projects and for thin panel cladding for new building, mainly for town and city office and retail buildings. The wholesale demolition of historic properties in Scottish cities during 1960s stimulated a vigorous conservation response from the public and since then planning requirements to maintain the local character of cities, towns and villages have created a demand for local stone. Initially this demand was satisfied by recovery from demolition but as the requirement for repair and conservation has increased, alternative supply options have been promoted. Consequently there has been a noticeable increase in the interest in, and the demand for, new resources of natural stone. Overall there has been a modest increase in the diversity of supply of local stones.

Flagstones (thinly laminated sandstones and siltstones) of Devonian age, quarried for paving stone, Spittal Quarry near Thurso, Caithness.
Flagstones (thinly laminated sandstones and siltstones) of
Devonian age, quarried for paving stone, Spittal Quarry near
Thurso, Caithness.

Building, paving and roofing stones, including slate, are naturally-occurring rocks of igneous, sedimentary or metamorphic origin which are sufficiently consolidated to enable them to be cut, shaped, or split into blocks or slabs for use as walling, paving or roofing materials in the construction of buildings and other structures, such as bridges and monuments. Most natural stone is quarried from bedrock which may be exposed at the surface or concealed by superficial deposits. Stone for building may also be taken from quarries whose main mineral product is extracted for other purposes. In the days of land improvement during the 17 th and 18 th century for agricultural purposes field boulders also formed important building and walling materials. Traditionally the varying characteristics of natural stone were effectively exploited thus allowing the best use of the resource from any one source. Thus for example, thinly bedded or laminated sandstone could be split or riven for pavement whilst thickly bedded and massive (structureless) sandstones allowed masonry block of a range of dimensions to be cut. With modern stone-cutting equipment today's industry is geared to cut thickly bedded and massive sandstone in dimensions suitable for many purposes including paving and cladding. The term natural stone does not include manufactured products, such as reconstituted stone or 'artificial' stone, although these are an increasingly important sector of the building materials market.

In Scotland a wide range of rock types is used as sources of building stone, including sedimentary sandstones, metamorphic slates, and some igneous rocks, principally granite and to a lesser extent dolerite. Limited resources of marble have been extracted mainly for ornamental uses. The suitability of a stone for building purposes depends not only on factors such as strength and durability, and commercial considerations such as the size of block or slab that can be extracted, but also on aesthetic qualities, such as colour and texture. Other factors, including the bed thickness, ability to polish, and ease of carving or sawing for mouldings, may also be important.

Demand

Two principal markets - new buildings and the repair and maintenance of historic buildings drive the demand for natural stone products .

  • New building involves both maintaining vernacular styles using materials that are compatible with traditional local building practices, or in contemporary design requirements including internal and external decoration. For new housing there is a trend towards utilising stone as rough finished cladding to fronts of buildings to provide an aethestic attraction which has a positive impact on property value. New build also includes prestige or major commercial work that may have a high-tech, contemporary or classical style where the use of any specific stone may be secondary to the proposed architectural impact.
  • Repair and maintenance of historic buildings and structures requires the use of material from the original or compatible quarry sources. This principle is in accordance with internationally recognised best conservation practice. The reasons are twofold, firstly to ensure that the introduction of replacement stone does not accelerate the natural decay processes in the original fabric and secondly to retain the character of the building - an important aspect of the built heritage which is appreciated by both local communities and visitors.

The market for stone for new building is small and specialised but relatively buoyant. Small builders have seen a growth in demand for individually designed stone-built houses that can command premium prices. There has been an increasing demand for a wider variety of building materials, including stone, throughout the house construction industry. Even where brick or block is the main walling material, details such as steps and lintels may be in stone. Interior fittings, for example granite worktops are also popular. In addition, stone is becoming more widely used in boundary walls and street furniture.

Scotland

England

Wales

Northern
Ireland

Isle of
Man

Total

Building sandstone

19

159

14

1

0

193

Building limestone, incl. Chalk

5

117

11

2

2

137

Granite & other igneous rocks

25

16

3

3

1

47

Slate & marble

1*

23

16

0

4

44

Ironstone flint, serpentine etc

3

14

1

0

0

18

* marble quarry. There are no slate quarries currently operating in Scotland.
Table 1 Distribution of active building stone quarries in the UK, March 2005.
Source: BGS

Scottish indigenous natural stone is highly sought after for large and prestigious building projects such as the Museum of Scotland, Edinburgh which employed Clashach Sandstone from Elgin for its rain-screen cladding, and the Scottish Parliament Buildings, Edinburgh which utilised Kemnay granite from Aberdeenshire. Caithness Flagstone continues to be widely used for recent streetscaping projects and there is now interest to investigate the possibility of reintroducing stone for paving from Angus, a county which traditionally supplied this material.

The heritage market is of increasing importance. Scotland has a large stock of historic stone structures that are protected by legislation that demands like-for-like replacement of stone wherever possible in conservation projects. These structures form an important part of the nation's cultural heritage and are a considerable attraction for both domestic and foreign tourists. In essence they provide a 'sense of place' and character to our cities, towns and villages. The need to protect, restore and conserve these buildings, many of which are built of indigenous stones, is recognised as an essential objective in the maintenance of landscape and townscape.

Natural building and roofing stone products are rocks quarried for the purpose of obtaining blocks or slabs that can be used non-dressed or subsequently dressed (shaped), riven (split) or sawn (ashlared) for general building. They include:

Stone cladding - material quarried, split, sawn and/or polished for non-load bearing walling material.

Kerbstone - stone used for edging roads and footpaths

Setts - stone roughly squared for roads and paving

Flagstone - quarried, sawn and split (riven) specifically for flooring or paving.

Slate - rock with a pronounced metamorphic (slatey) cleavage allowing it to be split into thin sheets - principally for roofing but also for decorative cladding and monumental use.

Stone slate - rock (other than slate) that is thinly bedded and fissile (easily split or riven into thin slabs) and quarried specifically for roofing purposes (includes flagstones and sandstones).

Monumental stone - rock quarried cut, split, dressed or polished specifically for use in monuments, gravestones or memorial tablets .

Decorative stone - rock quarried, sawn, worked and polished for (architectural) ornamentation - fireplaces, stone mouldings.

Marble - geologists only apply this term to limestones that have been altered by metamorphism, however, the building trade uses the term to include any limestone that is hard enough to provide a polished surface.

Walling stone - rock quarried for non-dressed (rubble) or dressed blocks.

Rockery stone - stone cobbles and boulders, of varied lithological composition, used in landscaping and gardening.

Supply

Quarries primarily producing building stone in Scotland vary significantly in size and output. They range from relatively large operations with areas in excess of 50 ha and operating continuously with a high face, to very small sites less that 0.5 ha in extent and worked occasionally to recover stone from a thin bed. In addition, almost all crushed rock aggregate quarries produce, or can produce, building stone. Larger operators, controlling several quarries commonly in different geological rock types may serve an extensive national (and sometimes international) market with production in the order of 5-10 000 tonnes yr. Small producers, usually operating a single quarry, principally serve local or national niche markets and have an annual production of less than 500 tonnes. Intermittent quarrying to supply specific projects is also a common form of working. The concept of 'snatch' quarrying developed in the 1980s with examples from Dundee and West Lothian where stone producers were granted planning permission for the extraction of stone for a specific duration before the quarry was closed.

Out of a total of 439 active building stone and slate quarries in the UK currently there are some 53 quarries in Scotland producing a range of building stone products. Products include dimension stone, paving stone, and stone for walling. The distribution of these quarries is shown in Table 1. Whilst the UK industry is still capable of meeting the current demand for natural stone there are some serious gaps in terms of supply of Scottish indigenous stone for the repair and conservation. Examples include the supply of slate. Scotland has had no working quarries in slate since the mid 1950s. Options for roof repair have included salvaging slate from the roofs of other buildings or utilizing slate of uniform size and textured character from England, Wales or the continent. Traditionally slated roofs on many Scottish buildings have employed indigenous slates of a range of dimensions, in diminishing courses. There is also a need to increase the supply of indigenous sandstone. Assumptions regarding the compatibility of replacement sandstones (e.g. from northern England) have tended to be made simply on aesthetic considerations. Recent research indicates that local sources of sandstone within the same geological and geographical setting are better matches for the original stone using mineralogical and porosity criteria.

The diverse nature of Scotland's stone built heritage has meant that many local stones are now no longer actively quarried. This shortage of local materials has already reached a critical point for some building stone materials (e.g. Craigleith Sandstone, West Highland slate). The Scottish Stone Liaison Group, with objectives to promote awareness of the stone built heritage and indigenous materials and skills training needs, is addressing the issues of reopening of quarries or opening new ones to supply indigenous stone. As a result, local authorities, landowners and users of natural stone are becoming more aware of the local resource potential and its value for repair, conservation and new build. An example of this proactive approach is the recent reopening of an historic quarry in Fife to supply sandstone of near identical properties to that of Craigleith Sandstone for repair work in Edinburgh. Research sponsored by Historic Scotland, is ongoing to address the resource potential of Highland slate formations to meet demand for roofing repair. In some cases, the demand for some natural stone may be only for local requirements or for specific projects. Whilst this may not justify either the environmental or the economic costs of opening disused quarries or starting new operations, a snatch quarrying policy (opening for short durations on a need basis) offers one solution to be considered.

Scottish production tonnages of the principal rock types for all uses (including aggregate) are shown in Table 2. Totals for building and roofing stone are highlighted. Some figures have had to be estimated because selected information is confidential. These figures should be treated with some caution, as they are believed to over estimate production, particularly with respect to igneous rock. According to the Annual Minerals Raised Inquiry there is slate production in Scotland. No figures are given for tonnage but returns have been received from West Central Scotland, Tayside and Fife and North East Scotland. It is possible that some flagstone products are being described as slate.

Sandstone represents Scotland's major building stone resource. Sources are focussed within geologically defined sedimentary basins in southern Scotland, the Midland valley (central belt), the Moray Firth and Caithness and Orkney. Sources of granite are available from Galloway and Aberdeenshire and dolerite from the Midland Valley. The principal slate belts are found in Lochaber and Easdale, in parts of north-east Scotland and along the line of the Highland Boundary Fault.

Trade

There are no separate trade statistics for Scotland. In common with the rest of the UK Scotland is a major net importer of dimension stone and slate and low cost imports are seen as the biggest threat to the indigenous natural building stone industry. These imports are primarily of material used in prestige construction projects, street furniture and internal decoration, and imports have not, as yet, significantly penetrated the market for stone for house building and walling. However, imports of paving material are increasing and imports of roofing and walling slate substantially exceed domestic production. Recently imported stone (for cladding and for street setts) and roofing slate have come from as far afield as India, China and Brazil. European sandstones are also making their appearance in new build projects. The durability of some foreign products has yet to be proven in the variable Scottish climate and further research may be needed into issues such as colour changes occurring of roofs employing imported roofing slates.

Currently much sandstone from Northern England is used in Scotland. Stemming from the introduction of English stone for new buildings in the late 19 th century, this source of supply to Scotland continued throughout the 20 th century and continues to be commissioned for new build projects requiring 'uniform' cladding. The presumption that these sources are also satisfactory for repair work to historic properties constructed of local sandstone has been challenged in recent years as a recognition that mineralogical and porosity differences are exacerbating decay processes existing stone masonry.

Consumption

The total UK market for natural stone is roughly of the order of one million tonnes a year. This figure is in sharp contrast to the 225 million tonnes of natural aggregates that are consumed in the UK each year. However, the unit value of building stone is much greater than for aggregate. The domestic building stone industry is broadly able to meet demand. However, imports are required for the more specialised types of dimension stone, notably limestone marble of which there are only minor indigenous resources, and also the many types of igneous rock used for cladding. Imports are increasingly penetrating other sectors of the market.

Year

Sandstone Total

Sandstone for building stone Total

Igneous rock Total

Igneous rock for building stone Total

Limestone Total

Limestone for building stone Total

Thousand Tonnes

1990

1834

10

19280

109

1778

-

1991

1555

na

19588

94

2018

-

1992

1658

9

20064

112

1410

-

1993

1716

30

20806

142

1432

-

1994

1772

22

20672

na

1650

-

1995

2400

15

21731

130

1540

na

1996

2172

11

19933

128

1607

-

1997

1712

8

19863

129

1624

-

1998

2539

17

20500

107

1535

na

1999

1657

14

21761

141

1507

na

2000

1715

na

21455

179

1722

na

2001

1603

18

20034

423

1733

na

2002

1645

na

20543

196

1635

1

2003

1481

63

20920

179

1730

na

2004

1613

28

23724

174

1746

na

2005

1466

33

23052

130

1746

na

Table 2 Scotland: Sales of building stone, 1990-2005
Source: Annual Minerals Raised Inquiry, Office for National Statistics
na: not available

The market for new building projects has fluctuated in recent years. The prestige sector has maintained a steady rate of production, recently boosted by involvement in numerous national and local regeneration projects, many being undertaken with Lottery Heritage Funding. The heritage repair market for stone is also growing. National and local planning regulations encourage, wherever possible, like-for-like replacement of stone in building conservation. New building, extensions to existing buildings, paved areas and walls within Conservation Areas are required to use materials compatible with the surrounding historic built environment. In addition, the desire to create a diversity of building form with a wider range of materials in new housing outside Conservation Areas has increased new build demand for natural stone.

Economic importance

Building stones have an inherently higher unit value than most other minerals produced in Britain. Prices can range from a few tens of pounds per tonne to several hundreds of pounds, with the ultimate price of a building stone being essentially a function of the degree of processing that the rock has undergone.

Total sales of building stone in Great Britain are reported by the Office National Statistics as £49 million in 2004, of which sandstone accounted for some 65%. This figure probably relates to the value of crude blockstone production (stone roughly squared at the quarry) and thus underestimates the true value of the industry. The value of roofing and cladding slate sales was about £47 million in 2004.

The total value of sales of worked or monumental stone and slate that has been cut, shaped or finished, was £367 million in 2004. Although this value includes sales of material imported into the UK for 'finishing' it provides a better indication of the true value of the industry. Building stone is a construction material and its ultimate value resides in the final product - the built environment.

Structure of the Industry

The industry is characterised by a relatively large number of fairly small producers. The Stone Federation Great Britain is the trade association that represents the industry in its widest sense. It has 159 members, which include importers of stone and stone products, and processors and masons, in addition to domestic natural stone producers. Most producers are single site operations and are not engaged in aggregate quarrying.

Sandstone (including flagstone)

A & D Sutherland

Block Stone Ltd

Caithness Stone Industries Ltd

Locharbriggs Sandstone Ltd

Moray Stone Cutters

Natural Stone Quarries Ltd

Orkney Island Council

Sutherland Stonework

The Hutton Stone Company

Tradstocks

Igneous (including granite) and metamorphic rocks

Bardon Aggregates - North and Scotland

Ennstone Thistle Ltd

Leiths (Scotland) Ltd

Tarmac Limited - Northern and Scotland

Limestone (including marble)

Ledmore Marble Ltd

Leiths (Scotland) Ltd

MacFadyens Contractors

There are many other stone companies based in Scotland, which are supplying both indigenous and foreign products.

Resources

Scotland has numerous geological formations that are potentially suitable for use as building stone. Reflecting geology, different parts of the country have distinctive rock types, which also results in the distinctive character of the built environment in these areas. This makes it difficult for building stones for repair and maintenance projects to be matched from alternative sources. Replacement stone is commonly specified on colour alone: good practice demands that stone matching should include mineralogical, grain size and structural compatibility to ensure that the new material is geologically the same as the original.

The principal building stone resources are listed in Table 3 and their distribution is shown in Figure 1. The apparent extensive nature of these resources disguises the fact that rocks suitable for use as building and roofing stone may be highly localised. This is a direct function of local geology where bed thickness and extent, incidence of discontinuities, such as fractures, and degree of cementation of the rock all have a fundamental effect on the suitability of the rock for building stone. As a result workable deposits may be difficult to find and where they do occur may be restricted in extent. Subtle or substantial lateral differences in stone properties can significantly affect the characteristics of the product. Minor changes in cementation or grain size may affect weathering properties and thus durability, which may be particularly important in restoration work or where a large façade needs to maintain a consistent effect. Changes in bed thickness alone within the same rock unit can create a different building product (block as opposed to thin slab), which, if used together, can totally alter the aesthetic aspects of structures and create an incongruous impact.

The major rock types that are used as sources of building stones in Scotland are:

  • Sandstones, formed by the weathering and erosion of all types of pre-existing rocks. These rocks consist of small fragments or grains held together by natural cements such as calcium carbonate (calcite), silica, iron oxide or clay minerals. Most sandstones consist of grains of quartz, feldspar and lithic (rock) fragments. It is their high quartz content that makes them hard, durable building stones. Sandstones can be divided into fine, medium or coarse-grained types by measuring the average size of the grains. Sandstones from the Devonian, Permian and Triassic are characteristically red because of the presence of iron-staining on the grains. Red sandstones have been traditionally exploited as building stone in Ayrshire, Arran, Dumfriesshire and the Borders. Devonian flagstones (thinly bedded sandstones) were greatly prized as sources of paving stone from Angus and from Caithness and Orkney. Pale grey and white coloured sandstones of Carboniferous age predominate in the Midland Valley: these have been extensively quarried for building stone for towns and the cities of Edinburgh and Glasgow. Hard greywacke sandstones (sometimes colloquially referred to as 'whin' or 'whinstone') of Lower Palaeozoic age in the Southern Uplands, have a high proportion of rock fragments. These sandstones are difficult to work but were used locally across the south of Scotland together with more easily dressed sandstone quoins and window dressings. The sedimentary structure and mineralogy of a sandstone can often distinguish whether it is of eolian (wind-blown dunes), fluvial (river channel) or marine origin. Importantly for building stone, mineralogical analysis can determine the clay mineral content and porosity of the material.
  • Igneous rocks, hard, crystalline rocks composed of the primeval material of the earth. These rocks formed directly by the cooling of hot molten magma of varying composition and under variable conditions of temperature and pressure that consequently produce a very wide spectrum of rock types. They are widely used as building stone but are commonly termed ' granites' by the trade . Scientifically, however, igneous rocks show a range from pale-coloured, coarsely-crystalline, quartzo-feldspathic varieties, that include the true granitic rocks, used as building stone in Galloway and Aberdeenshire (including Aberdeen - the 'Granite' City), to dark coloured, finely crystalline basic or basaltic rock types and dolerites, typically found in the Midland Valley of Scotland. The latter have been used extensively both for local building work and as kerb stones and setts. Other igneous rocks used for building or decorative purposes include coarse grained granodiorites, diorites, syenites, gabbros and monzonites.

Sandstones

Principal producing counties

Triassic (red & white)

Dumfries & Galloway, Fife and Moray

Permian (red)

Dumfries & Galloway

Carboniferous

Fife, Scottish Borders

Devonian (Old Red Sandstone - red purple sandstone; grey flagstone)

Caithness, Angus

Lower Palaeozoic (greywacke sandstone)

Scottish Borders and Dumfries & Galloway

Limestones

Pre-Cambrian

Highland, Skye, Grampian

Slate

Lower Palaeozoic (stone 'slate')

Dumfries & Galloway, Scottish Borders

Pre-Cambrian

Argyll & Bute, Aberdeenshire

Granites & other igneous rocksAberdeenshire, Argyll & Bute, Fife, Highland; Dumfries & Galloway

Table 3 Principal building stone resources in Scotland.

  • Metamorphic rocks, hard rocks such as gneiss, schist and quartzite recrystallised under high pressure and temperature. These rocks occupy large tracts of ground to the north of the Highland Boundary Fault. Traditionally used locally for rubble construction, they were difficult to dress and were not exploited for national markets. Although structurally complex, and often extensively joined, Scottish metamorphic rocks offer potential for new building stone projects in the Highlands.
  • Slates, fine-grained, low-grade metamorphic rocks showing strong fissility (i.e. slatey cleavage) which allows the rock to be split into thin sheets of consistent lithology. Slates are formed by the recrystallization of fine-grained sedimentary or igneous rocks (usually volcanic ash) under extremes of temperature and pressure. Under such conditions, which develop over many millions of years, new minerals, most notably micas, grow and the characteristic slatey cleavage is formed. It is the alignment of these new minerals that enables the slates to be easily split into thin sheets. An important feature of metamorphic slates is their lack of porosity, which makes them impervious to fluid flow. In Scotland, the West Highland Slate industry focussed on Ballachulish and Easdale: there is potential to reopen former quarries or consider new sites to supply a growing repair market in Scotland.

Figure 1 Distribution of the principal building stone resources of Scotland and the location of active quarries.
Figure 1 Distribution of the principal building stone resources of Scotland and the location of active quarries.

Other rock types which have had limited use as building stone in Scotland include:

  • Limestones, principally composed of calcium (calcite) and/or magnesium (dolomite) carbonate. These rocks are relatively soft in comparison to sandstones and are not found in abundance in Scotland. Limestone was exploited in the past for agricultural purposes, lime mortars and limited supplies of masonry. Today it is used for cement manufacture. There is little potential as a building stone. Most limestones are formed by the accumulation on the seabed of the broken shells of marine organisms, in tropical or sub-tropical settings. These bioclastic grains are cemented together by natural calcium carbonate. In coarse-grained limestones, fossil shell fragments are easy to see with the naked eye. Also included in this group of rocks are the magnesium-rich or dolomitic limestones. The Durness Limestone of North West Scotland is an example. Dolomitic limestones are principally formed by the chemical alteration of an original calcium-rich limestone. This alteration process may preserve any original shelly or ooidal limestone fabric or completely destroy it to produce a crystalline rock.
  • Marbles, limestones that have been recrystallised by metamorphism. The building trade uses the term to cover any hard, polishable, limestone. Metamorphosed limestones (marbles) are texturally and colourfully distinctive but they are still principally composed of calcium or magnesium carbonate. Rare occurrences of marbles in the Scottish Highlands (e.g. Ledmore) have been used for decorative purposes.

Reserves

Total reserves of building, paving and roofing stone with planning permission are not available for reasons of commercial confidentiality. However, quantifying building stone reserves is difficult. This is because of variations in the physical quality, geometry and lateral continuity of different rock units and irregular joint and bedding planes, all of which can markedly affect yields. Indeed yields may not be quantifiable until the stone is extracted.

Significant reserves of sandstone are likely to be present in Dumfriesshire, parts of the Midland Valley and around the Moray Firth. There are also significant reserves of flagstones in Caithness. There is also potential for exploitation of reserves in Angus (flagstone for paving and thicker bedded sandstone for masonry). The traditional areas of granite exploitation in Galloway and in Aberdeenshire offer some potential. Slate reserves are present in the west Highlands.

Relationship to environmental designations

Large areas of Scotland are covered by national landscape and nature-conservation designations. Any development in these areas is subject to rigorous examination. Many of these areas coincide with building stone resources and current and former operations. Notable examples include granite within the Cairngorms National Park, and slate and other metamorphic rocks within the Loch Lomond & Trossachs National Park.It is important that mineral extraction does not adversly affect the qualities for which landscape or natural heritage areas may be designated.

Stone used in buildings, walling and other structures frequently forms a prominent element in the visual character and cultural history of protected landscapes.

Scottish Planning Policy 4 aims to safeguard minerals so far as possible for future use, encourage sustainable working practices and to minimise adverse impact on communities in the environment. The SPP recognises the importance of non-aggregate construction mineral such as building stone.

Extraction and processing

Building stones are mainly extracted by surface quarrying. Underground mining, where overburden became too great for surface working, was undertaken over 100 years ago at a few former quarries (e.g. Giffnock and Bishopbriggs, Glasgow).

Unlike in aggregate quarrying, where the objective is to reduce the stone to small fragments, blasting is now almost never used in the extraction of building stone as the requirement is to recover large blocks from the quarry face that can be subsequently dressed. Blasting could have a serious detrimental effect on the structure of the softer stone varieties if not undertaken with care. The quarry face is initially opened up using limited quantities of explosive placed in shallow holes drilled at intervals on the upper surface of the rock. The naturally occurring lines of weakness, provided by joints and / or bedding planes, in the rocks determine the maximum size of the blockstone that can be produced. Large blocks produced are reduced in size by hammer and chisel, drilling and the use of iron wedges ('plug and feathers') or by diamond wire saw techniques. However, for some monumental and prestige work very large blocks (more than 2 m on bed) may be specifically sought. In most sedimentary rocks, blocks are recovered directly from the face by mechanical excavators. Joint and bedding plane surfaces rarely provide a near cubic/rectangular block and more typically will produce rhombic shapes that need careful cutting to maximise saleable block and minimise waste.

The new National Museum of Scotland, Edinburgh, opened 1998, with rain screen cladding in Permian sandstone from Clashach Quarry, near Elgin, Morayshire.

The new National Museum of Scotland, Edinburgh, opened 1998,
with rain screen cladding in Permian sandstone from
Clashach Quarry, near Elgin, Morayshire.

Processing of the stone begins at the quarry or following transportation to centralised cutting sheds depending on the requirements of the contract. Softer stones, such as limestones, can be shaped and roughly dressed by hand or cut using a handsaw or mechanical guillotine at the quarry. Harder stones may need to be sawn using frame-saws, gang-saws, diamond rotary blades, diamond wire saws or high pressure water-jets. Surface finishing of some stones can involve polishing using abrasives and flame-jet texturing. Riven stone is produced by hand and there is a still a demand for stone processed in this way to impart roughness of texture on a Scots-slated roof or for a rough non-slip finish for paving.

By-products

Some building stone quarries also produce armourstone and rockery stone. The extraction and processing of building stone generally involves the production of a large proportion of mineral waste, sometimes in excess of 80% of the raw material extracted. As a result, aggregates are produced, to a greater or lesser extent, at the majority of building stone operations, although the technical properties of this material mean that it is often only suitable for lower value aggregate applications.. The amount of by-product aggregate produced from building stone operations is. Use of this material improves overall resource utilisation, replacing primary aggregate that might be extracted elsewhere. However, it may also result in greater impact on the environment than would be associated with building stone production on its own. However, using mineral waste removes the disproportionately large and sometimes prominent, stockpiles that may be visually intrusive, delay restoration or will be tipped on other land.

Building stone is also produced as a by-product of an increasing number of aggregate quarries and also a few sites producing cement raw materials. This activity requires careful planning of the life of a quarry, ensuring that suitable quarry faces are set aside and protected from explosive blast damage to allow the extraction of building stone.

Alternatives/recycling

Building stones are valued for their physical properties, such as colour, texture, strength and durability. These properties are generally unaltered in use and thus building stones can be readily recycled into other structures. As such, natural building stone is a more sustainable commodity than manufactured products. Building stones were one of the very first products to be recycled by man. This sometimes resulted in the destruction or damage of historical structures. Recycling continues to be a problem today with the theft of building stone and slate from existing structures. Stone recovered by recycling derelict building was formerly the major source of local stone for house building, although the quality of recovered stone may be variable due to weathering.

As individual types of building stone often have very distinctive characteristics they cannot be easily matched by stone from alternative sources. Maintaining a supply of local stone is, therefore, important in maintaining local vernacular styles of architecture.

Concrete, brick and steel are alternative construction materials, although they cannot be viewed as alternatives to natural stone, which supplies a valued added market. The production of 'artificial stone' or 'reconstituted stone' products has increased substantially in recent years and compete directly with natural stone in some markets. Crushed rock fragments bonded together by lime, cement or organic resins are now a commonplace, cheaper alternative to natural building stone. The roofing industry has used concrete tile products for some time but recently the use of 'tiles' made by blending of natural rock fragments or synthetic materials with cements or resins to replace both natural stone and metamorphic slates has become more commonplace. Similar products are also produced for paving. In many cases the raw materials used in these products are derived from the waste produced at building stone quarries. These 'alternatives', although cheaper, lack the aesthetic qualities of natural stone products.

Effects of economic instruments

The Aggregates Levy was introduced in April 2002 at the rate of £1.60/t. Although building and roofing stone are exempt, sales of waste rock from building stone quarries as aggregate are subject to the Levy, irrespective of whether the aggregate is a mineral waste from quarrying or processing. It is reported by the industry that the introduction of the Levy has had an adverse effect on sales of these low-grade aggregates, which can command only low prices, resulting in disposal problems at the quarry.

Planning issues

The location of building stone resources is determined by geology and it is important to ensure that access to deposits, which may be of commercial interest, is safeguarded. The extent of natural stone resources should be understood, not just in terms of quality and location, but also in relation to environmental constraints. Safeguarding does not necessarily indicate acceptance of working. However, deposits considered unacceptable for working under today's technology may be acceptable with future technology. Policy should therefore be based on the following principles:

  • Mineral resources are finite and care must be taken to safeguard those deposits which are or may be of commercial interest against other types of permanent development which would either sterilise them or be a serious hindrance to their extraction.
  • Other development proposals should be phased wherever possible in order that sufficient opportunities are allowed for mineral extraction.

With variation in scale of quarrying operations the impacts and planning issues associated with building stone extraction can also show marked differences. This variation is further increased by locational considerations. Quarries may have to be located prominently in exposed uplands or coastal situations where climatic conditions are more severe making operational conditions, landscaping and restoration more difficult. Alternatively it may be possible to locate a new quarry where topography and vegetation screen operations successfully.

Quarries, particularly those with a long history, may now suffer from urban encroachment constraining development options and sterilising valuable and scarce resources. Shifting economic conditions may now mean that nearby property is no longer occupied by the quarry workforce but by those who have no interest in the continuation of production.

The impacts of the extraction of building and roofing stone cannot, therefore, be simply categorised. Generally, impacts are much less than for the quarrying of aggregates or other major opencast operations mainly because the scale of extraction is much smaller. Associated impacts on amenity, such as noise, dust, mud and transport, are also not so great, although transport of block may actually only involve a small tonnage per movement thus increasing the total number of movements. Actual impacts will vary from site to site, depending not only on output but also location with respect to sensitive designations and the rock type being produced and the amount of associated waste.

Sweetheart Abbey, New Abbey, Dumfries and Galloway, a late 13th and early 14th Century Cistercian abbey constructed of local Permian red sandstone.
Sweetheart Abbey, New Abbey, Dumfries and Galloway, a late 13th
and early 14th Century Cistercian abbey constructed of local Permian red sandstone.

Further information

Scottish Planning Policy 4. Planning for Minerals

National Planning Policy Guideline NPPG 18: Planning and the Historic Environment

Technical Advice Notes and research reports and Inform Guides by Historic Scotland www.historic-Scotland.gov.uk

Building with Scottish Stone (2005) a publication of the Natural Stone Institute www.nsiuk.org

Scottish Stone (2006), published by UNESCO Publishing, International Association of Engineering & Environmental Geology, Historic Scotland, British Geological Survey

Other useful websites

Scottish Stone Liaison Group
www.sslg.co.uk

Stone Federation Great Britain:
www.stone-federationbg.org.uk

Building Research Establishment:
www.bre.co.uk

Department for Communities and Local Government
http://www.communities.gov.uk

Authorship and Acknowledgements

This factsheet was produced by the British Geological Survey for the Scottish Executive. It was compiled by Andrew McMillan, Ewan Hyslop, David Highley, Don Cameron, and Gill Norton (British Geological Survey) and Alan McKinney (Scottish Stone Liaison Group), with the assistance of Deborah Rayner ( BGS).

The advice and assistance of the industry is gratefully acknowledged. Mineral Planning Factsheets for a range of other minerals produced in Scotland are available for download free of charge from www.mineralsUK.com

© Crown Copyright 2007.

Unless otherwise stated all illustrations and photographs used in this factsheet are BGS© NERC. All rights reserved.