Dolomite, also known as dolostone, is a sed-imentary carbonate rock, consisting mainly

of the mineral dolomite [CaMg(CO3)2]. Rockscontaining only 10–50% of the mineral dolomiteare called dolomitic. Most, if not all, dolomite isa replacement of pre-existing limestone andthis replacement process is known as dolomiti-

sation. The process is often incomplete androcks termed 'dolomite' are usually a combina-tion of dolomite, dolomitic limestone and lime-stone. Dolomite deposits are, therefore, usuallyassociated with limestones. This fact, togetherwith the presence of variable amounts of impu-rities, such as silica, sulphur, iron oxides andalumina, has an important bearing on the suit-ability of dolomite for specific applications.

Dolomite has a number of uses, the mostimportant of which, by volume, is in construc-tion, where it may substitute for limestone.However, for some uses dolomite is specificallyvalued for its magnesia (MgO) content, andchemical composition is all-important.

Industrial dolomite is a commercial term fordolomite used for non-construction purposes

where its chemical properties (or degree ofwhiteness) are important. The MgO content ofdolomite is commonly expressed after calcina-tion (heat treatment involving the removal ofcarbon dioxide). Pure dolomite has an MgOcontent of about 40%. However, glass manufac-turers normally use pre-calcined MgO contentfor control purposes and there is a theoreticalmaximum of about 21.8% MgO. Dolomite forindustrial purposes accounts for a relativelysmall and decreasing proportion of totaldolomite output. Like limestone, dolomite usedin construction is a low-value commodity,which does not normally lend itself to longtransport distances, although this may not betrue for high-quality industrial dolomite.

Demand

The principal uses of industrial dolomite, firstlyas a refractory and later as a flux, have beenlinked with iron and steelmaking since the lat-ter part of the 19th century. For this reasonindustrial dolomite has been regarded as ofvital importance to the iron and steel industry.The other major markets for dolomite are inglassmaking and for agricultural use (Figure 1).

Raw dolomite and calcined dolomite have anumber of different uses in the iron and steelindustry. However, changes in iron and steel-making technology during the 20th centuryhave had a marked effect on the demand fordolomite for specific uses and the market con-tinues to evolve.

The principal uses of dolomite are those thatutilise the mineral in the calcined form(dolomitic lime). The most important of these isas a steelmaking slag flux, where the dolomiticlime replaces some of the quicklime (CaO) usedin slag production. In addition to increasing slagfluidity, the presence of magnesia also helps toprotect, and thus improve the life of, the steelvessel’s refractory linings, which are made ofmagnesia. The total quantity used has beendeclining in line with a fall in iron and steel pro-duction. Some 260 000 tonnes of calcineddolomite were used for this purpose in 2004.

Hard burnt dolomite, which is subsequentlyformed into pellets and fired again to achieve a

Dolomite

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Mineral Planning Factsheet

Dolomite

Dolomite is used asa soil conditioner inagriculture.

This factsheet pro-vides an overviewof industrial

dolomite supply inthe UK. It is one ofa series on eco-nomically impor-tant mineralsextracted in Britainand is primarilyintended to informthe land-use plan-ning process.

January 2006

(Table 1 updatedAugust 2006)

Dolomite

Dolomite 2

higher bulk density, is used in the manufactureof dolomite refractory bricks. Dolomite refracto-ry bricks are no longer produced in the UK butcalcined dolomite is exported to Germany andTurkey for this purpose. Low levels of silica andiron oxides are required for this use. Anotherform of calcined dolomite with added ironoxide is used to repair furnace linings.

Dolomitic lime was formerly used on a sub-stantial scale for the manufacture of seawatermagnesia principally for refractory use at aplant in Hartlepool. However, the production ofrefractory magnesia ceased in 2002. Productionof chemical grade magnesium oxide powdersand magnesium hydroxide suspensions contin-ued until June 2005, when the seawater plantcompletely closed.

The use of raw dolomite as part of the flux bur-den in ironmaking has been replaced by anigneous rock containing a high proportion ofthe mineral olivine [(Mg, Fe)2SiO4], which inaddition to supplying magnesia, also con-tributes silica. However, raw dolomite may beintroduced as a flux directly into the BasicOxygen Steelmaking vessel where it alsoreplaces steel scrap as a coolant.

For many of the applications in the iron andsteel industry there are strict limits on thechemistry of the dolomite used, which mainlyneeds to be low in silica (often <0.55% SiO2) or<0.3% for some applications, with low iron(<0.55% Fe2O3), sulphur (<0.1%) and phospho-rus (<0.02%).

Another important market for industrialdolomite is in glassmaking. Most commercialglasses consist essentially of silica togetherwith soda (Na2O) and lime (CaO), the limebeing partly replaced by magnesia (MgO) forsome purposes. Lime is introduced into theglass melt as limestone (CaCO3) and magnesiaby adding dolomite [CaMg(CO3)2]. However, inthe flat glass industry most lime is introducedwith the dolomite and only a little limestone isused to balance the CaO/MgO ratio. Lime andmagnesia improve the durability of the glassbut magnesia also inhibits the devitrificationprocess, which is particularly important in themanufacture of flat glass. Dolomite is also used

in container glass. A critical factor in the supplyof any glassmaking raw material, includingdolomite, is iron content as this is a seriousimpurity in the manufacture of colourlessglasses. In contrast to silica sand, mineral pro-cessing cannot effectively lower the iron con-tent of dolomite (or limestone). Although theUK has high quality limestone resources withvery low iron contents (see factsheet onIndustrial Limestone), there is a deficiency oflow iron dolomite resources, which only rarelyhave iron contents as low as 0.2–0.25% Fe2O3.Imported dolomite, with iron contents of lessthan 0.03% Fe2O3, is required for the manufac-ture of colourless glass containers and, some-times, low iron float glasses.

Dolomite is relatively soft and easily crushed toa fine powder, which is used as agriculturallime (‘aglime’) by farmers to reduce soil acidityand also to adjust magnesium deficiencies.Dolomite is equally good as limestone in neu-tralising soil acidity, but the element magne-sium is itself also an important plant nutrient.Two types of aglime are produced (unburnt andcalcined).

Dolomite is also used for a range of filler appli-cations in plastics, paints, rubbers, adhesives

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Mineral Planning Factsheet

Dolomite 12.2 Mt

Industrial/agricultural 1.4 Mt

INDUSTRIAL DOLOMITE SUPPLY 2004

Constructional use10.8 Mt

Calcination (Dolime)

Steelmaking Flux

Glass making Fillers

Agricultural Industrial

Steelmaking Refractories

Seawater Magnesium Oxides &

Hydroxides (Now ceased)

Figure 1 Principal uses of dolomite and

dolomitic lime.

and sealants. Dolomite is finely ground to pre-cise size specifications. Pure white (high bright-ness) filler grades are preferred but these arerare in the UK.

Most markets for industrial dolomite aremature markets, or are in decline, due to thedecline in UK manufacturing. A notable excep-tion is the manufacture of flat glass. Exportmarkets for dolomite are, therefore, of consid-erable importance.

Supply

Production data for dolomite for industrial andagricultural use have not been disclosed sepa-rately for a number of years, because of com-mercial confidentiality considerations.However, a combined figure is available andabout 1.4 million tonnes of dolomite werereportedly produced for industrial and agricul-tural use in 2004. Total production of dolomitein the UK in 2004 was 12.2 million tonnes,most of which was used in construction.Almost all of the dolomite produced in the UKis sourced from quarries working Permiandolomites in Durham, South Yorkshire andDerbyshire. Minor quantities are producedfrom dolomites of Carboniferous age inShropshire, Derbyshire, Gloucestershire andSouth Wales, although not for industrial use.Dolomite is an important soil conditioner but

Dolomite

Dolomite

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0

500

1000

1500

2000

2500

3000

3500

4000

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

Thousand tonnes

Figure 2 Great Britain: Dolomite production

for industrial and agricultural purposes,

1980–2004. Source: Annual Minerals RaisedInquiry, Office for National Statistics.

Exports Imports

Tonnes £thousand Tonnes £thousand

1999 91 489 4 358 228 874 4 198

2000 112 875 4 947 174 353 3 798

2001 131 073 4 653 188 312 3 671

2002 104 126 4 393 184 948 3 694

2003 35 804* 1 677 179 003 4 129

2004 24 736* 1 271 170 888 3 631

2005 126 022 4 411 215 990 4 019

* These figure are incomplete because some data are confidential.

Table 1 UK: Imports and exports of dolomite, 1999–2005.

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Dolomite

Dolomite 4

the largest industrial uses are in the produc-tion of calcined dolomite (dolomitic lime) andfor glassmaking.

Production of dolomite for industrial use hasdecreased significantly in recent years (Figure2) due to an overall decline in iron and steelproduction following the closure of theRavenscraig and Llanwern iron and steelworks,the cessation of dolomite refractory brick pro-duction and the closure of the Hartlepool sea-water magnesia plant. In addition, the use ofdolomite for sinter feed for ironmaking hasbeen replaced by imported olivine.

Trade

The UK is a net importer of dolomite (Table 1).Exports, consisting of both calcined dolomitefor use in steel making and refractories, andagricultural dolomite, are to a number of coun-tries, but mainly the Republic of Ireland, IvoryCoast, Netherlands and Germany (official fig-ures from HM Revenue & Customs). Imports areof high purity, low-iron dolomite mainly fromSpain and Norway for use in glass manufacture.Imports of calcined dolomite are minimal.

Consumption

Most (89%) of the dolomite used in the UK isfor construction use where chemistry and mag-nesium content is not important. Magnesiumoxide content and the levels of impurities pres-ent are important for industrial and agriculturaluses. Total consumption for these applicationshas declined significantly in recent years and isabout 1.4 million tonnes, although this figure isbelieved to be somewhat underestimated. Nomajor increases in demand are anticipated.

Economic importance

The long association of dolomite with the ironand steel industry has meant that the mineralhas been regarded as of considerable econom-ic importance. Despite a decline in usage, steel-making remains the major market for dolomiteboth for use as a flux and refractory raw mate-rial. Because of the restricted distribution ofsuitable quality dolomite for these applications,certain sites will remain of considerable eco-

nomic importance. In addition, dolomite is animportant raw material in the glass industrywhere it is used notably as an essential con-stituent of flat glass.

Structure of the industry

There are a limited number of industrialdolomite producers in the UK (Figure 3).Lafarge Aggregates Ltd owns and suppliesmost of the rock for industrial dolomite produc-tion from three quarries; Whitwell Quarry inDerbyshire, Thrislington Quarry in CountyDurham and Cadeby Quarry near Doncaster.The actual production of industrial dolomite isby Steetley Dolomite Ltd, which now owns andoperates the kilns at Whitewell and Thrislingtonquarries and is the only UK producer ofdolomitic lime for the steel industry. SteetleyDolomite Ltd was formed in 2004 following amanagement buyout of the manufacturingoperations, including kilns, that formed LafargeLime, i.e. Whitwell in Derbyshire andThrislington in Durham. The Whitwell plant pro-duces only hard burnt refractory dolomitewhilst the Thrislington plant produces onlydolomitic lime, principally for use as flux in thesteel industry. Lafarge has retained the quarriesat Whitwell and Thrislington, which also supplylarge quantities of aggregate. LafargeAggreagates also supplies dolomite to OMYAUK, which operates a grinding plant at CadebyQuarry to supply dolomite for glassmaking andfiller and agricultural uses. Warmsworth (TheDolomite) Quarry, also near Doncaster, is oper-ated by WBB MINERALS Ltd and suppliesdolomite to the glass industry, principally forflat glass manufacture. All of these sites alsoproduce dolomite for agricultural use, some forexport, and crushed rock aggregate. Dolomitefines produced at several other crushed rockaggregate quarries are also sold for agriculturaluse.

Britain’s sole seawater magnesia plant atHartlepool closed in June 2005.

Resources

Permian dolomites are the main source ofdolomite in the UK and are a resource ofnational and regional importance. Dolomite D

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Mineral Planning Factsheet

also occurs in some parts of the Carboniferouslimestone sequence but in most areas thedolomitisation is not sufficiently extensive, orof consistently high grade, to form a resourceof industrial dolomite. In sharp contrast to thelarge resources of high-purity limestone thatoccur in the UK, dolomite resources are oflower chemical purity notably with respect toiron content which is only very rarely in therange of 0.2–0.25% Fe2O3. However, a low ironcontent is not critical for all applications.

Dolomites and dolomitic limestones of latePermian age crop out as a narrow, easterly dip-ping, north-south belt running for some 230 kmfrom Newcastle to Nottingham (Figure 3). Itcomprises a series of dolomites, dolomiticlimestones and limestones up to 300 m thick.The sequence is highly variable, both regional-ly and locally, in its geology, and chemical andphysical properties and thus in its suitability forparticular applications. Impurities such as silica,iron oxides and alumina are a prime considera-tion in the selection of dolomite for industrialapplications, and some industrial uses alsorequire a relatively hard stone. Dolomites withsufficiently low levels of impurities to be usedas a flux in steelmaking, for refractory use andglassmaking are comparatively scarce in theUK.

In north-east England (County Durham), theRaisby Formation and Ford Formation areimportant carbonate resources. The RaisbyFormation at Thrislington Quarry is a majorsource of high-grade dolomite for steelmaking.Other quarries in these formations providelocal sources of aggregates, with quarry finesbeing used as aglime. In South Yorkshire,Derbyshire and Nottinghamshire, the Permiansequence is made up of two carbonate units(the Cadeby and Brotherton formations) sepa-rated by calcareous mudstone. The total thick-ness (mostly <125 m) is much less than inCounty Durham. The Cadeby Formation isbetween 30–70 m in thickness and consists of avaried sequence of dolomites and limestones.Most quarries in the formation produce aggre-gate, but locally near Doncaster it is of higherpurity, with a low iron content, and is extractedfor glassmaking at Warmsworth and Cadebyquarries. It is also of relatively consistently high

quality near Worksop where it is quarried atWhitwell for use in manufacturing refractoryproducts. The quality of the stone is variableand selective quarrying of specific horizons isrequired to ensure that the stone meets the dif-fering raw material requirements.

The Carboniferous limestone has been dolomi-tised, or partially dolomitised, in many parts ofits outcrop and in some areas the dolomitisa-tion is sufficiently extensive to form a dolomiteresource. In the Peak District of Derbyshire alarge area of Carboniferous limestone betweenMatlock, Monyash and Brassington has beendolomitised, although it is of variable thicknessand quality. There is currently no production ofindustrial dolomite from these rocks, althoughthey are locally of relatively high purity andmay be of sufficient quality locally to be suit-able for glassmaking. Dolomitic limestone ofCarboniferous age is also extracted nearOswestry in Shropshire mainly for constructionuse, although some is sold as aglime. SomeCarboniferous dolomite is also produced inGloucestershire for agriculteral use.

Carboniferous limestones containing dolomiteresources of commercial significance are foundin South Wales, cropping out around the flanksof the South Wales Coalfield. To the south of thecoalfield, along its eastern fringes in the TaffsWell-Risca-Pontypool area, the whole limestonesequence is dolomitised and has been workedat a number of quarries. The dolomites hereare generally much finer and denser thandolomitised Carboniferous limestones else-where and hence produce strong and durableaggregate. However, they have limited use as asource of industrial dolomite. Dolomite occursinfrequently in North Wales, but has beenworked on a small scale near Llandudno foragricultural purposes.

In contrast to the rest of the UK, Scotlandpocesses few limestone resources. The DurnessLimestone in north-west Scotland is mainly ofCambrian age and is worked at Ullapool fordolomite which is sold mainly for aggregateand agricultural purposes. In Skye metamor-phosed Durness Limestone known as SkyeMarble is worked at Torrin for dolomite, whichis largely used for agricultural applications.

Dolomite

Dolomite

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Dolomite

Dolomite 6

Dolomite is unusual in the Dalradian lime-stones of Scotland, with the exception of theAppin Limestone, which is reported to bedolomitic in most outcrops.

Dolomite is not produced in NorthernIreland, but resources occur within the mainCarboniferous limestone units in Fermanaghand Tyrone.

Reserves

Permitted reserves of industrial dolomite needto be considered on a site-by-site basis, andalso by their suitability for specific applica-tions. Permitted reserves at current sites rangefrom less that 10 years to some 15 years sup-ply. Plants producing industrial dolomite, andparticularly those with kilns for calciningdolomite, require a large capital investment ofthe order of tens of millions of pounds.Ongoing capital investment is over one millionpounds a year. Permitted reserves shouldreflect this large investment.

Relationship to environmental designations

The Permian dolomites are not covered byany national landscape designations butresources are constrained in part by natureconservation designations. However, atThrislington Quarry an SSSI (limestonegrassland) was successfully translocated toanother piece of land within the companyownership. Cadeby Quarry is a geologicalSSSI and the type locality for the CadebyFormation. The adjacent Sprotborough Gorge isan also SSSI. The Creswell Crags SSSI boundsWhitwell Quarry to the south.

Extraction and processing

Dolomite is extracted by surface quarryingusing drill and blast techniques although break-ing by impact hammer is used at one opera-tion. The dolomite is selectively quarried at sev-eral distinct levels, known as 'benches', to man-age the stone quality, which may vary consider-ably in chemistry and hardness. Lower qualitydolomite is sold for construction use, althoughthe dolomite forming the top bench atThrislington Quarry is soft and mainly waste

rock. Processing can be simply divided intocrushing, screening, grading and storage priorto loading and transportation. However, vari-ous grades of dolomitic lime are produced atThrislington and Whitwell quarries by burningthe stone in rotary kilns at very high tempera-tures in the range 1450°C–2000°C. Residencetimes in the kiln are between 3.5 and 6 hours.At such high temperatures the dolomite istransformed from the double carbonate

Mineral Planning Factsheet

Thrislington

WarmsworthCadeby

Whitwell

Industrial Dololomite Resources

Industrial dolomite quarry

Permian, dolomite and dolomitic limestone

Carboniferous, dolomites (Derbyshire and S Wales)

Cambro−Ordovician, Durness Group, dolomites

Figure 3 Distribution of principal industrial

dolomite resources.

(CaCO3.MgCO3) to the oxide form (CaO.MgO),with carbon dioxide being driven off as a gas.Depending on the product being produced,additives, mainly iron, are also injected into thekiln. For refractory brick manufacture thedolomite goes through a second sintering (fir-ing) stage after being pelletised to achieve thehigh bulk densities necessary for refractoryuse. Lower temperature calcination produces amore reactive, dolomitic lime suitable for useas flux. Distinct size fractions (typically 38 mm–19 mm and 19 mm–8 mm) are required forburning. This is a factor of some practicalimportance in that the yield from crushing toachieve suitably sized stone for burning can beas low as 45% because of losses into the fines.These fines, including fines generated in thekiln, are sold for agricultural use.

A critical factor in dolomite used for glassmak-ing is consistency in quality and notably in ironcontent. A major feature of processing is, there-fore, achieving a consistent product by careful-ly controlled blending.

By-products

All industrial dolomite quarries also producesignificant quantities of crushed rock aggre-gates. The largest quarries producing industrialdolomite are Thrislington and Whitwell andeach quarry produces over 1.2 million tonnesannually. The proportion of dolomite going forindustrial use is generally less than 50% of thetotal. The fines from quarrying dolomite bothfor industrial and construction use are typicallysold as aglime.

In Durham the Permian Yellow Sands crop outintermittently at the base of the Permianescarpment and dip to the east beneath thedolomite. They consist of fine to medium-gradesand and comprise a resource of fine aggregatemainly used as building sand. The sand ismainly worked in association with the overly-ing dolomite, for example where they areexposed in the base of Thrislington Quarry.Permian limestones overlie concealed coal-bearing strata and some coal extraction hastaken place in the floors of large dolomite quar-ries in Durham.

Alternatives/recycling

Dolomite is valued for its magnesia (MgO) con-tent and it is this, which distinguishes it fromlimestone. It can be partly substituted for bylimestone for certain applications, although inpractice it is dolomite that tends to replacelimestone. Dolomite and limestone both neu-tralise soil acidity but only dolomite can correctmagnesium deficiencies in the soil.Magnesium, like calcium, is a plant nutrient. Asa flux in steelmaking, dolomitic lime also con-tributes magnesia and this imparts additionalbenefits, notably protection of the steel vessellinings from chemical wear. In ironmaking,however, olivine has largely replaced dolomiteas a lime-free source of magnesia for use as aflux and slag conditioner.

In glassmaking both lime and magnesiaimprove durability, but magnesia is essential inimproving the devitrification properties ofsome glasses (e.g. float glass). Dolomite is anessential raw material for float glass manufac-ture and there is normally no economic alterna-tive.

One of the main advantages of dolomite as araw material is that it is relatively inexpen-sive. Dolomite, because of its low price,remains the popular choice when availablelocally. However, the use of dolomite over itslimited mineral alternatives is dependent onthe mineral's purity and its proximity to themarket.

Effects of economic instruments

Dolomite that is used for prescribed industrialand agricultural processes is not subject to theAggregates Levy.

Transport issues

Most dolomite is transported by road, usingbackhaul opportunities where feasible. BothThrislington and Whitwell quarries have raillinks, but only the rail link at ThrislingtonQuarry is in use. Substantial quantities of steelflux are transported by rail to Port Talbot steelworks in South Wales. Some dolomite is trans-

Dolomite

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Dolomite

Dolomite 8

ported by rail to Scotland for soil conditioning.Elsewhere dolomite is transported by road,either loose or in bulk tankers, or packed inindividual bulk bags. Some bulk shipments aremade overseas but mostly it is exported insealed containers.

Planning issues

Resources of higher purity dolomite anddolomitic limestone are more scarcely distrib-uted than high purity limestone. However, thedemand for dolomite is significantly lower.Industrial dolomite is currently produced atonly four sites in the UK but constraints onquality mean that indigenous dolomite is not ofsufficient purity for all applications and importsare required. The close association of the usesof dolomite with iron and steelmaking, both asa flux and refractory, has meant that the miner-al is considered to be of considerable nationalimportance. Both Derbyshire and Durham havemade provision to protect resources at the twomain sites (Whitwell and Thrislington).Consequently, in allocating reserves, MineralPlanning Authorities, have wished to see thesemaximised for industrial end uses. However, allsites also produce substantial amounts ofaggregate from inferior quality dolomiteunsuitable for industrial use. In addition,because of particle size requirements for kilnfeed material, the yield of calcined product canbe as low as 50%.

Processing dolomite, and particularly high tem-perature calcination, requires substantial capi-

tal investment in plant. Longer-term security ofsupply issues are, therefore, of concern to theindustry.

Authorship and acknowledgements

This factsheet was produced by the BritishGeological Survey for the Office of the DeputyPrime Minster to support the research project‘Review of Planning Issues Relevant to SomeNon-Energy Minerals other than Aggregates, inEngland’ (2004). It was updated as part of theresearch project ‘ODPM-BGS Joint MineralsProgramme’.

It was compiled by David Highley, AndrewBloodworth (British Geological Survey) andRichard Bate (Green Balance Planning andEnvironmental Services), with the assistance ofDon Cameron, Paul Lusty and Deborah Rayner.

The invaluable advice and assistance of theminerals industry in the preparation of this fact-sheet is gratefully acknowledged.

Mineral Planning Factsheets for a range ofother minerals produced in England are avail-able for download from www.mineralsUK.com

© Crown Copyright 2006.

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

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Mineral Planning Factsheet