NGU-BULL 436, 2000 - PAGE 15 Natural stone in Norway: production, deposits and developments TOM HELD AL & PE ER R. NEEB Heldal, T. & Neeb, P. R. 2000: Natural sto ne in Norway: produc tio n, deposits and developments. Norgesgeologiske undersokelseBulletin 436, 15-26. The natural sto ne industry has, during the last two decades, experienced a tremendous growth both on a glo bal scale and wit hin a Norwegian context. At th e present time, the natura l stone industry contributes significantly to total Norwegia n mi neral production and export. The production of larvikite is, by far, the most important part of the indu stry, followed by slate and metamorphic flagstone . Future reserves of these important resources are considered to be large. In addition, a diversified natural stone industry aimed for local and dome stic markets is growing in most parts of th e country, driv en by an increased useof stone fo r building sdome stically, and by th e need for paving stones in urban areas. There exists a considerable pot enti al for th e develop ment of new natu ral stone depo sits, as well as revitalising old quarries in the light of the expanding and increasingly diversified use of sto ne. However, t he possibilities for th e develop ment of new deposits for export-oriented produ ction is probab ly limited to a few geological provinces containing unique rock types. Environmental issues and land use regul ations will undoub tedly influence natu ral sto ne exploitation in Norway, and there are conside rable futur e challenges concerning the handling of waste from product ion,'peaceful' co-existence between industry and community, and th e integration of informat ion on natural sto ne deposits into plans fo r land use. Tom Heldal & Peer Richard Neeb, Norgesgeologiskeundersekelse, N-7491Trondheim, Norway. depend s mo re on t he consumer's personal taste and on fash­ Introduction ion tre nds th an t he chemical and physical quality of the Building sto ne differsfrom ot her mineral resources in several material concerned . ways. First of all, sto ne quarrying isabo ut the art of collecti ng In many places around th e world, t he stone industry is w hole, massive pieces of rock, w it hout the need for crushing based on the collect ion and shaping of field stones and sim­ and grinding and separation of individual minerals. Furth er­ ple quarrying of soft and hard sto ne for local building pur­ more, stone pro cessing does not includ e removal of poses. For small-scale. local-market production of stone, the 'unwanted' compo nents from t he rock; it simply deals with a basic requirement s are rocks th at are easily worked wit h a more or less advanced way of shaping pieces of rock into fin ­ min imum of labour (Shadmon 1997). An attractiv ely col­ ished products . In addition, th e market for stone products oured granite is not of commerci al interest if it takes an excessive number of working hou rs to shape a block or a Natural stone brick for construct ion. A 'boring', grey granite may, however, be very interesting if th e cleavage properti es facilitate th e shaping of the blocks. This perspective differ s comp letely from th e search for stone for the internat ional market. Most of th e expo rt quality stone of th e wo rld ends up as polished slabson floors, walls and astom bstones.The aesthetic aspect (e.g. th e colour and st ruct ure of t he rock) is here far more important in th e pricing of stone th an physical prop erties. Predominantly, rare colours such as blu e, yellow, pu re white and deep black are high ly priced, w hilst rocks of mor e 'ordi­ nary' colours obtain lower prices. For raw bloc ks, t he most exclusive rocks may be 20 times more expensive th an the cheapest. All over the world we have seen, during th e last decades, an expanding business in stone, both for local/ domestic and for int ernational markets (Conti et al. 1990). This is not only because of a short-term fashion able tr end, but rather more a 'catching up' on 70 years of concrete hegemony in const ruc­ t ion. Building ston es are often classified according to their Fig. 1. Industrial classificatio n of natural stone (ty pes found in Norway) . technical quali ty and usability. A standardised, internation al NGU-BULL 436, 2000 - PAGE 16 TOMHELDAL& PEERR.NEEB classification scheme do es not exist, but it is common, as tate the extracti on process. The structural features are also of shown in Fig. 1, to differe nt iate between massive stone importance to the commercial value ofthe fin ished products. (extracted in large blocks) and slabby stone, extracted as Foliated or layered rocks will obviously have improved tech ­ slabs which are cleaved along a planar str ucture,such assedi­ nical properties when cut parallel to the lami nation instead mentary layerin g or metamorphi c foliation . Massive stone is of perpendicular to it. In addit ion, the colour and structure, further divided into 'soh' varieties such as carbonates and which contri bute to the aesthetic qua lity, vary accordin g to serpentinite, and 'hard',essentially quartzo-feldspath ic rocks. cutt ing directions. In some extreme cases, rocks must be cut in a specific direction to have any com mercia l value at all, such as the Norwegian larvikites. Exploitation of natural stone Another important aspect in the production of rough The most important aspect in th e exploitation of natural blocks for the intern ational market is the need for heavy stone deposits is th e need for ext racti ng large and whole machinery in the qua rries (Fig. 2). A standard size for trad e bloc ks and slabs of rocks w ith a uniform quality. This is don e blocks is 2.4 x 1.2 x 1 m (ca. 8 tonnes ). Most suppliers will be by wedging, careful blasting and primary sawing, or a combi­ asked for even bigger sizes, up to 30 tonnes, to feed the giant nati on oft hese met hods (Figs. 2 and 3). Sawing, especially by frame saws in Italy or oth er coun tr ies pro ducing finished diamond w ire, is most applicable to rocks wi th low or inte r­ products. The bloc ks should be well-shaped and rectangular, mediate hardne ss, such as limestone, marble, slate and ser­ with no veins, cracks or inclusions. For small blocks and pentin it e, but is also wi dely used for feldsp athi c igneous bloc ks with such 'faults', the price may be reduced by up to rocks and, to some extent , also for granit es. However, blast­ 70% if one is fortunate to find a buyer for them. ing and wedging is still th e mo st common extraction method The need for large blocks creates a waste problem in nat­ for hard siliceous rocks. Some of these rock types have excel­ ural sto ne qua rries, and generally the percentage of waste is lent natural splittin g prop erties due to more or less visible well above SO%. In some Norwegian quarries, it may be as structural anisot ropic feat ures, such as directionally distrib­ high as 95%. The prop ortion of waste is a good ind icator of uted minera ls or microfractu res. Experienced quarry workers extract ion costs, whi ch in Norway vary from USD 150 to USD know how to make use of t hese directio ns in order to facili- 1000 per m3 for commercial blocks, reflect ing differences in uniformity, fracture density and splitting properties.Only the most exclusive rock types can be produced at such a high 3 unit cost. For most granites, prices (per m ) are lower than USD 500, and thu s the waste ratio should be below 80 % and the deposits hom og enous and massive. The varying price for raw blocks is highly dependent on t he colour of th e rocks; rare colours give higher prices on the world market. Blue, yellow, deep black and pure wh ite are among the most expensive colo urs, whilst pink and grey rocks are low-priced. Generally speaking, all rocks showing an attractive play of colou rs, such as iridescence in feldspars, are highly priced. Fig. 2. Larvikite quarry, close to Larvik, Southeast Norway. A combination Important geological aspects in the of drillin g/bl asting, diamond wi re sawing and wedging is applied in th e evaluation of natural stone deposits extractio n process. Given the comp lex market mechanisms for natura l ston e, including local needs for raw materials, as well as trends and behaviou r of the glo bal market, some knowledge of markets for finished products is a prerequisite in geological investiga­ tions ofstone deposits. In any case, there are some important geological aspects that need to be focused upon, includin g: Geological aspects influencing the uniformity ofrock col­ our and structure, such as veins and dykes, inclusions and segregati ons, foliations and layering and other structural eleme nts. Geological aspects influencing the block and slab size, such asfracture density, folds,'open' foliations, remanent st ress field s and weat heri ng and deloading features. Geolo gical aspects influencing the quality ofthe rocks, in th e shorter or long er terms,such as deteriorating miner­ Fig. 3. Diamond wire sawing applied in th e Lovgavlen marb le quarry, als and minerals causing staini ng oft he rock (e.g.