Geological History for the Larvikite fra Magne Marthinsen
The history of larvikite goes back a long time. The larvikite is deposited in the area history of the earth called Permian. The larvikite is a rock which origin from a melt that was initiated on the border between the earth’s crust and the viscose mantel, and later forced itself through the crust. Deep down the melt it had a lower density than the crust, and the melt started to ascend through weak zones in the crust created by movements between the continental plates. On the way up the hot intrusion partly melted the rocks it forced itself through, and eventually got the same density as the crust. The shape of this kind of intrusion will be as a mushroom. The intrusion is thought to have been deposited at several kms depth.
The condition of crystallisation was so that the two different feldspars formed intimately together in microperthites instead of forming discrete separate feldspar crystals. The difference in optical properties in the two feldspars causes the special colour effects which make the larvikite so special among the rocks of the world.
The mineral grains are oriented so that their largest crystal plains will be perpendicular to the highest pressure during the crystallisation. When the rock intrudes up through the crust the inner thriving force will pressures against the surroundings and make currents in the intrusion. The grains will orientate themselves with the biggest crystal planes against the outer part of the mushroom shaped intrusion. Normally the customers want the large crystal planes with colour variations. The crystallisation starts in the outer part of the intrusion because the environment is colder than the central part of the ascending magma.
Occasionally one can observe bands with dark mafic minerals and light crystals of feldspar. This shows that there have been a gravitative segregation of the magma due to the difference in density of the two types of minerals. The dark minerals has higher density than the light ones and will descend downwards into the melt. The rest of the melt will become lighter and continues to rise higher in the crust than it would without the process. This also leads to the amount of feldspar increases compared to the dark minerals upwards in the intrusion.
There are outlined 10 different circular intrusions (fig.1) of larvikites and lardalites from Tønsberg in the east to Porsgrunn in the west. The oldest intrusion is found in the eastern part. It is red in colour, and contains minor amount of quartz. The youngest intrusion is in the north-western part of the area around the place Lardal, and the rock is named lardalitt. The lardalite is grey without the colours typical for the larvikite. These intrusion are dated to be between 277+/-3 and 269+/-5 mill. Years.
There are several types of commercial larvikite. One type is a dark green blue larvikite that is sold under the name of Emerald Pearl on the international stone market. This rock is mostly homogenous and is found in the Tjølling area. Blue larvikite is the other main type, but this type is much more inhomogenous, and has several different names due to texture and colour. The geographical extension of blue larvikite is relatively extensive from Tjølling in the east to Eidanger in the west. Three areas are commercially exploited. The biggest volume is in the Tvedalen-området where the rock is called Blue Pearl. In addition there are quarries in Stålaker, where the rock is called Marina Pearl, and there are quarries in Malerød/Vardåsen, which is situated north of E18 between Larvik and Porsgrunn.
The reason that the larvikite today is exposed is that the surface erosion has eroded away the rocks above. The features which are on the surface today is mostly created by the glaciers that existed in several periods between 100.000 and 10.000 years ago (fig2a og 2b).
Only between 5 and 15% of the material can be sold with adequate quality. The remaining blocks have default and colour variations which make the polished end product of reduced quality for building purposes.There are numerous reasons why the waste is such a large portion. The movement in the crust which caused the formation of the Oslo field continued later and made vertical NS going faults. The large faults going NE-SW and NW-SE are caused by movements related to the earlier Caledonian mountain range. There are also sub horizontal fault which in geological term are much younger than the above mentioned. These faults are caused by land release and repeated ice ages. The flat faults are normally parallel to the topography.
Another phenomenon which causes reduced quality is open texture. This phenomenon appear as small discontinuous cracks more or less parallel to the biggest crystal planes, and appear in the upper 10-20 meters of the quarries. The default may be formed by repeated load and release of big masses of glaciers during the last 100.000 years. There are crosscutting veins of different colours and grain sizes which reduce the homogeneity quality of the rock. These veins have their origin in interstitial melts in between the crystals. Cracks are made due to reduction of volume from liquid to solid, and due to movements in the crust. The interstitial melts will force themselves upwards in these small cracks and make veins. These melts have extremely high viscosity and will flow very easily in small weak parts of the rock. The veins are occurring in several generation which the younger ones are cutting the older ones. Small cracks with mineral fillings can also be observed. These cracks also occur in several generations and are probably caused by movements in the crust after the magma has crystallised completely. Intrusions of other rock types (ex. black diabas) are found occasionally specially in the Blue larvikite.
Development of exploitation:
The first use of blocks of larvikite was in the older times where it was used for small local fortresses, memories of Kings, among other things. The first art from older time was made in larvikite as rock carvings. The first mentioning of commercial quarries of larvikite was in Nicolai Thychsens Chemical Handbook which was given out in Copenhagen in 1794. The first commercial use was in basements of houses, among them the church farm in Tjølling from 1805. The first quarry was opened by engineer Erik A. Gude on Lamoya, Viksfjord in Tjølling in 1888. After one year the quarry workers was moved to Varild in the inner part of Viksfjord in Tjølling. The year after mayor of Brunlanes, Louis Narvesen, establishes quarries in Varild, Vik and Klåstad, all within the area. Thereafter several quarries are established in the following years.
After the war Stålaker is established. Swedish firms are among the earliest to start up quarries in the Tjølling area. With these firms experienced and skilled workers from south Sweden and Østfold are coming in to the area. These new workers was quickly integrated with the locals. In 1920s and 30s there were hard times in Norway, and many workers started in the quarry-industry because there was no other work. Together with economical difficult times family tradition have played an important role for recruitment in time between the wars. The work in the quarries was very hard physically. Everything was done by hand. The drill holes were done by workers who hit the drills with big sledgehammer, and the drills were turned between every hit. To cool down the drill water was used. The workers had small tin cans with holes which were placed close to and poured water down the drill hole. Small pieces of pine trees were tied together and placed above the drill holes to prevent spraying of water and save water. To prevent the water from freezing during the winter, the workers added salt. A worker who drilled 1 meter an hour had a good days pay. The most skilled worker could do 12-15 meters a day, 8-10 meters was normal. The first mechanised drill rigs was made in the 1920s, and was driven with steam. Pneumatic equipment was used first time in 1928, and full mechanisation was complete after the war. Black powder or dynamite was used to free the blocks from the quarry. In the beginning they used bars and manual muscle power to lift the blocks, and then keels was used so that the blocks wouldn’t fall down again. To loosen the blocks underneath up to 10 workers with bars would lift the block. One strong worker with a big sledgehammer would insert a keel while the workers with the bars lifted the block. The keel was hit so that the small upward movement the block made was maintained, and didn’t fall down to the next lift. It was important to keep the beat so that the sledgehammer hit the keel at the same moment the block was lifted. These work could take hours with good teamwork. In the beginning of the quarrying, rollers of wood were used to transport the blocks within the quarry. Later on the cranes were installed. The cranes were driven by hand force and dragged through the quarry up to the place where the blocks were trimmed. When they were finished they were put in stock. Waste blocks were moved by special workers which were called “busær” or “busrær”. When the blocks were drilled, or when blocks were to be moved by bars, it was important to have the workers do things simultaneously. Singing was a good way of keeping the beat. No special tradition was developed in the quarries, but among the workers some “rallere” had come from railroad building tradition to Larvik. Songs from that railroad building was extensively used. The workers sang to the stone which made the work go faster and easier. All the old still living workers said that the singing was a nice part of the working day. The beat in the songs were used as a measure for the intensity of work by which they were paid. If one on the guys works faster than the beat, the other told him to slow down.
In the early days there were no cabins in the quarry were the workers could warm up during the winter or eat their lunch. Old workers describes how they cut down trees and made their own shelters were they eat and made coffee with open fire. The house where the blacksmith worked was a pleasant place to stay. The competition between 2-3 big companies and 16 small ones in Tjølling, was extensive. The price was driven down, but still they had few problems of selling their products. Transportation out of the quarry started with big trolleys. When big blocks were transported kasteblokker were used. They were fixed on big poles made of stone and put up along the roadside. Horses were used as power. Blocks up to 16 tons were transported from Hasle quarry to Lauve railway station 1 km. away. The block was placed on a trolley and the rail the trolley was moving along was advanced in front as it progressed. The transportation could last the night through. For transportation of regular blocks four horses were used, for the big blocks (10-12 tons) they used six horses. In addition to transportation by rail there was also build a key in Vikerøysundet in Tjølling which could load ships up to 600-700 tons. The stone was very much used to house founding. When a house was to be constructed, the construction workers tried to find a quarry as close as possible to the construction site. The first founding were moved with bars, later on different kind of cranes were used. The last commercial based founding was put up in 1946, the founding had become too expensive.
Today around 85% of the volume of produced rock is used for building purposes like polished slabs for cladding of office buildings, kitchen tops, bathrooms, tiles for different purposes. In Korea polished slabs are even used for mattresses in beds. A large part is also used for outside decorations. Around 15% is used for gravestones and monuments. The larvikite has a long tradition as excellent material for artwork. Many artists came to Tjølling to find stones for special sculptures. That meant a lot of work for local stone workers. The artist seldom made all the manual work themselves. There has always been a good relationship between artists and quarry workers. Gunnar Janson often visited Tjølling to find suitable stone. Janson rented a cabin in the Hasle-quarry during the war. He worked also in the Bergan-quarry. One of his most famous sculptures is that of Arne Garborg. Among other well-known artists that worked with stone from Tjølling were Odd Hilt, Stale Kyllingstad and Orrestad. The Ulabrand sculpture is placed in Ula. The initiative to the sculpture was taken by Tjølling Song Union. Hans Holmen made the artwork and it was finished in 1932. The raw material came from Fjellheim quarry at Hovland, close to Larvik centre. Hans Holmen made other famous sculptures like Myllarguten which is to be seen at Nordagutu Railway station (1938). The war monument by Hans Holmen is placed at the Bommestad bridge at E-18. Blocks to the victory monument planned by Hitler was taken out in Tjølling. These blocks were later split up and sold.
The turnover from the quarries in the Larvik areas has increased steadily except from some small depression periods. In 1958 the turnover was approx. 30 mill. Norwegian crowns, where 10 mill. crowns was for export. In1988 the turnover was approx. 230 mill. crowns, and in 1994 approx. 450 mill. crowns, which in weight is about 190.000 tons. Today the export part is more than 95%. The stone industry in Larvik employed in directly 360 persons in 1994, i.e. 7,5% of the industry workers in the county.