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58-557: The elevation of this region varies from 750 to 1,400 m and the annual rainfall ranges from 350 mm in the west to 600 mm in parts of the northeast. There are four significant mountain ranges in this region: the Magaliesberg which runs from Rustenburg in the west to Bronkhorstspruit in the east and forms the southern border of the Bushveld; the Drakensberg escarpment that forms

116-541: A curved prominence that intersects suburban Pretoria before it peters out some 50 km (31 mi) to the east, just south of Bronkhorstspruit . The highest point of the Magaliesberg is reached at Nooitgedacht , about 1,852 metres (6,076 ft) above sea level. A cableway reaching to the top of the mountain range is located at Hartbeespoort Dam , providing sweeping views of the Magaliesberg and surrounding area. The Magaliesberg has ancient origins. Its composition

174-434: A drop of dilute hydrochloric acid is dropped on it. This distinguishes dolomite from limestone, which is also soft but reacts vigorously with dilute hydrochloric acid. Dolomite usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Dolomite is usually granular in appearance, with a texture resembling grains of sugar . Under

232-405: A high percentage of CaMg(CO 3 ) 2 in which natural caves or solution tubes have formed. Both calcium and magnesium go into solution when dolomite rock is dissolved. The speleothem precipitation sequence is: calcite , Mg-calcite, aragonite , huntite and hydromagnesite . Hence, the most common speleothem (secondary deposit) in caves within dolomite rock karst , is calcium carbonate in

290-544: A high-calcium limestone, such as manufacture of sodium carbonate . Dolomite is used for production of magnesium chemicals, such as Epsom salt , and is used as a magnesium supplement. It is also used in the manufacture of refractory materials . As with limestone caves , natural caves and solution tubes typically form in dolomite rock as a result of the dissolution by weak carbonic acid. Caves can also, less commonly, form through dissolution of rock by sulfuric acid . Calcium carbonate speleothems (secondary deposits) in

348-566: A result, attempts to precipitate dolomite from seawater precipitate high-magnesium calcite instead. This substance, which has an excess of calcium over magnesium and lacks calcium-magnesium ordering, is sometimes called protodolomite . Raising the temperature makes it easier for magnesium to shed its hydration shell, and dolomite can be precipitated from seawater at temperatures in excess of 60 °C (140 °F). Protodolomite also rapidly converts to dolomite at temperatures of 250 °C (482 °F) or higher. The high temperatures necessary for

406-453: A very high ratio of calcium to magnesium. Dolomite is used for many of the same purposes as limestone, including as construction aggregate ; in agriculture to neutralize soil acidity and supply calcium and magnesium; as a source of carbon dioxide ; as dimension stone ; as a filler in fertilizers and other products; as a flux in metallurgy ; and in glass manufacturing . It cannot substitute for limestone in chemical processes that require

464-468: Is a nature reserve above Rustenburg covering 4,257 ha (10,520 acres) of the Magaliesberg. Numerous smaller reserves, private and state, are to be found along the length of the range. After nearly a decade of lobbying and sustained efforts by a small committee of dedicated environmentalists, the Magaliesberg has been declared a World Biosphere Reserve . The announcement was made on 9 June 2015 in Paris by

522-473: Is ascribed to successive geological processes over a very protracted history. Its quartzites , shales , chert and dolomite were deposited as sediments in an inland basin on top of a 3 billion year old Archaean Basement Complex, known as the Kaapvaal Craton . This process of sedimentation lasted for about 300 million years. About 2 billion years ago, a massive upwelling of molten magma resulted in what

580-467: Is characterized by its nearly ideal 1:1 stoichiometric ratio of magnesium to calcium. It is distinct from high-magnesium limestone in that the magnesium and calcium form ordered layers within the individual dolomite mineral grains, rather than being arranged at random, as they are in high-magnesium calcite grains. In natural dolomite, magnesium is typically between 44 and 50 percent of total magnesium plus calcium, indicating some substitution of calcium into

638-533: Is due to the Bushveld igneous complex , an extremely rich saucer-shaped geological formation that stretches over more than 50,000 square kilometers. This formation contains most of the world's reserves of minerals such as andalusite , chromium , fluorspar , platinum and vanadium . The complex includes the Merensky Reef , which is the world's biggest source of platinum as well as platinum-group metals. As most of

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696-466: Is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 66 million years in age). One of the first geologists to distinguish dolomite from limestone was Déodat Gratet de Dolomieu; a French mineralogist and geologist whom it is named after. He recognized and described the distinct characteristics of dolomite in the late 18th century, differentiating it from limestone. Most dolomite

754-487: Is mostly traditional , with a small number of sport climbing venues and hundreds of routes across a wide range of grades . The relatively mild climate allows year-round climbing. Dolomite (rock) Dolomite (also known as dolomite rock , dolostone or dolomitic rock ) is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite , CaMg(CO 3 ) 2 . It occurs widely, often in association with limestone and evaporites , though it

812-626: Is no consistent trend in its abundance with age, but most dolomite appears to have formed at high stands of sea level. Little dolomite is found in Cenozoic beds (beds less than 65 million years old), which has been a time of generally low sea levels. Times of high sea level also tend to be times of a greenhouse Earth , and it is possible that greenhouse conditions are the trigger for dolomite formation. Many dolomites show clear textural indications that they are secondary dolomites, formed by replacement of limestone. However, although much research has gone into understanding this process of dolomitization ,

870-423: Is not seen to precipitate in the oceans. Likewise, geologists have not been successful at precipitating dolomite from seawater at normal temperatures and pressures in laboratory experiments. This is likely due to a very high activation energy for nucleating crystals of dolomite. The magnesium ion is a relatively small ion, and it acquires a tightly bound hydration shell when dissolved in water. In other words,

928-506: Is now known as the Bushveld Igneous Complex . The enormous weight of this intrusion depressed the sediments that lay beneath and tilted the sediments along the edges so that the broken escarpments faced outward and upward, and the gentler dip slopes inward. During the same period, these sediments were fractured and igneous intrusions of dolerite filled the cracks. With the passage of time these intrusions eroded, especially on

986-419: Is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater , but it can still develop solution features ( karst ) over time. Dolomite rock can act as an oil and natural gas reservoir. Dolomite takes its name from the 18th-century French mineralogist Déodat Gratet de Dolomieu (1750–1801), who was one of the first to describe

1044-416: Is secondary, formed by replacement of calcium by magnesium in limestone. The preservation of the original limestone texture can range from almost perfectly preserved to completely destroyed. Under a microscope, dolomite rhombs are sometimes seen to replace oolites or skeletal particles of the original limestone. There is sometimes selective replacement of fossils, with the fossil remaining mostly calcite and

1102-538: Is stained by Alizarin Red S while dolomite grains are not. Dolomite rock consisting of well-formed grains with planar surfaces is described as planar or idiotopic dolomite, while dolomite consisting of poorly-formed grains with irregular surfaces is described as nonplanar or xenotopic dolomite. The latter likely forms by recrystallization of existing dolomite at elevated temperature (over 50 to 100 °C (122 to 212 °F)). The texture of dolomite often shows that it

1160-543: Is subject to high rates of evaporation. This results in precipitation of gypsum and aragonite , raising the magnesium to calcium ratio of the remaining brine. The brine is also dense, so it sinks into the pore space of any underlying limestone ( seepage refluxion ), flushing out the existing pore fluid and causing dolomitization. The Permian Basin of North America has been put forward as an example of an environment in which this process took place. A variant of this model has been proposed for sabkha environments in which brine

1218-630: Is sucked up into the dolomitizing limestone by evaporation of capillary fluids, a process called evaporative pumping . Another model is the mixing-zone or Dorag model, in which meteoric water mixes with seawater already present in the pore space, increasing the chemical activity of magnesium relative to calcium and causing dolomitization. The formation of Pleistocene dolomite reefs in Jamaica has been attributed to this process. However, this model has been heavily criticized, with one 2004 review paper describing it bluntly as "a myth". A 2021 paper argued that

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1276-467: Is the dry season throughout most of Southern Africa. The undisturbed portions of this habitat, such as much of the Waterberg Biosphere , are home to many large mammal species including white rhino , black rhino , giraffe , blue wildebeest , kudu , impala and a variety of additional antelope species and other game. The Bushveld is one of the most mineral -rich regions of the world. This

1334-476: Is thermodynamically favorable, with a Gibbs free energy of about -2.2 kcal/mol. In theory, ordinary seawater contains sufficient dissolved magnesium to cause dolomitization. However, because of the very slow rate of diffusion of ions in solid mineral grains at ordinary temperatures, the process can occur only by simultaneous dissolution of calcite and crystallization of dolomite. This in turn requires that large volumes of magnesium-bearing fluids are flushed through

1392-527: The Hartbeespoort Dam , situated in one of the valleys of the range, was completed. It became a popular holiday and weekend destination for the inhabitants of Johannesburg and Pretoria, and the villages of Hartbeespoort and Kosmos developed as a result. At present, the Magaliesberg area is still largely agricultural , although tourism is a rapidly growing industry in the area. Kgaswane Mountain Reserve

1450-574: The Matabele . As he feared an attack from Shaka if he returned home, he settled in the Magaliesberg region. On 17 January 1837, after some Voortrekkers had been attacked and killed by Mzilikazi's impis , they counter-attacked and, under the leadership of Hendrik Potgieter and Gerrit Maritz , and with the help of local Sotho- Tswana chiefdoms, drove the Matabeles north across the Limpopo River . Because

1508-706: The International Coordinating Council of the Programme on Man and the Biosphere (MAB). This is a UNESCO programme that aims to build a supportive and sustainable relationship between people and their environments. In effect, this means a specific focus on safeguarding natural ecosystems through innovative approaches to economic development. The World Network of Biosphere Reserves , which Magaliesberg now joins, counts 631 biosphere reserves in 119 countries. "We are delighted with this final acknowledgement of

1566-655: The Magaliesberg in the Highveld, leaving the Bushveld north of the Magaliesberg mostly to their Sotho-Tswana friends and allies; according to Sarah Heckford's memoir, A Lady Trader in the Transvaal , the Boers would move into the Bushveld to visit their Sotho-Tswana neighbors during the winter. According to oral testimony by Tswana headmen recorded around the turn of the 20th century, many individual Boers formed close friendships with prominent individual Tswana headmen and chiefs, especially for

1624-431: The Magaliesberg mountains is Dithaba Diloka . This is a local seTswana name in reference to the abundance of Heteropogon contortus which grows in the area. However it seems this name would have only been used by neighbouring Sotho-Tswana_peoples coming to and from the Magaliesberg mountains. Local resident Tswana tribes referred to it simply as Dithaba "The mountains" . The first European explorers who came to

1682-702: The Second Anglo-Boer War . The Boers, being extremely familiar with the mountains, used secret pathways across the mountains to launch guerrilla attacks on the British soldiers . In response, the British forces built blockhouses on top of the mountains in order to restrict the movement of the Boer forces; ruins of these structures are still to be seen on the mountain. Control of the Magaliesberg Mountain Range

1740-455: The area recorded the mountains being called the "Cashan" or "Kashan" mountains. This was a corruption of the name of a powerful chief of the BaKwena ba Mmatau whose name was Kgwasane wa Sekano (Kgwasane, son of Sekano) . In the mid-1800s the mountain range became known as Magaliesberg (lit. Mogale's mountain) after Kgosi Mogale . Mogale means "sharp" or "brave" person, but is also

1798-643: The common word for a warrior or Tswana soldier, in Sotho bogale means "sharp" and mogale is "brave" . Similarly, the mountain range to the north, near Sun City, Pilanesberg, was named after the local Bakgatla chiefs, who were called Pilane . In 1822, Shaka , the leader of the Zulu Kingdom , sent his most trusted commander, Mzilikazi , to conquer the Sotho tribes of the region. After accomplishing this task, Mzilikazi decided to break away from Shaka and found his own nation,

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1856-656: The dip slopes, forming deep kloofs or ravines providing rock-climbing potential to modern man. This large dog-leg-shaped area is now termed the Transvaal Basin and includes the lofty escarpment of the Transvaal Drakensberg overlooking the Lowveld in the eastern part of the country. Massive outpourings of igneous material–volcanic lava–of the much younger Karoo Supergroup later covered the Transvaal Basin, but this

1914-662: The eastern border of the Bushveld and runs from Tzaneen in the north to Belfast in the south; the Waterberg range that is in the middle of the Bushveld and the Soutpansberg range just north of Louis Trichardt . The latter is the northernmost mountain range in South Africa. As implied by the region's name, the Bushveld's grassy plains are dotted by dense clusters of trees and tall shrubs. The grasses found here are generally tall and turn brown or pale in winter (May to August), which

1972-531: The formation of dolomite helps explain the rarity of Cenozoic dolomites, since Cenozoic seawater temperatures seldom exceeded 40 °C. It is possible that microorganisms are capable of precipitating primary dolomite. This was first demonstrated in samples collected at Lagoa Vermelha , Brazil in association with sulfate-reducing bacteria ( Desulfovibrio ), leading to the hypothesis that sulfate ion inhibits dolomite nucleation. Later laboratory experiments suggest bacteria can precipitate dolomite independently of

2030-479: The forms of stalactites , stalagmites , flowstone etc., can also form in caves within dolomite rock. “Dolomite is a common rock type, but a relatively uncommon mineral in speleothems”. Both the 'Union Internationale de Spéléologie' (UIS) and the American 'National Speleological Society' (NSS), extensively use in their publications, the terms "dolomite" or "dolomite rock" when referring to the natural bedrock containing

2088-404: The greater temperatures characterizing deeper burial, if a mechanism exists to flush magnesium-bearing fluids through the beds. Mineral dolomite has a 12% to 13% smaller volume than calcite per alkali cation. Thus dolomitization likely increases porosity and contributes to the sugary texture of dolomite. Dolomite is supersaturated in normal seawater by a factor of greater than ten, but dolomite

2146-437: The magnesium ion is surrounded by a clump of water molecules that are strongly attracted to its positive charge. Calcium is a larger ion and this reduces the strength of binding of its hydration shell, so it is much easier for a calcium ion than a magnesium ion to shed its hydration shell and bind to a growing crystal. It is also more difficult to nucleate a seed crystal of ordered dolomite than disordered high-magnesium calcite. As

2204-461: The magnesium layers. A small amount of ferrous iron typically substitutes for magnesium, particularly in more ancient dolomites. Carbonate rock tends to be either almost all calcite or almost all dolomite, with intermediate compositions being quite uncommon. Dolomite outcrops are recognized in the field by their softness (mineral dolomite has a Mohs hardness of 4 or less, well below common silicate minerals) and because dolomite bubbles feebly when

2262-451: The mechanism of dolomitization, the tendency of carbonate rock to be either almost all calcite or almost all dolomite suggests that, once the process is started, it completes rapidly. The process likely occurs at shallow depths of burial, under 100 meters (330 ft), where there is an inexhaustible supply of magnesium-rich seawater and the original limestone is more likely to be porous. On the other hand, dolomitization can proceed rapidly at

2320-571: The microscope, thin sections of dolomite usually show individual grains that are well-shaped rhombs , with considerable pore space. As a result, subsurface dolomite is generally more porous than subsurface limestone and makes up 80% of carbonate rock petroleum reservoirs . This texture contrasts with limestone, which is usually a mixture of grains, micrite (very fine-grained carbonate mud) and sparry cement. The optical properties of calcite and mineral dolomite are difficult to distinguish, but calcite almost never crystallizes as regular rhombs, and calcite

2378-427: The mineral. The term dolomite refers to both the calcium-magnesium carbonate mineral and to sedimentary rock formed predominantly of this mineral. The term dolostone was introduced in 1948 to avoid confusion between the two. However, the usage of the term dolostone is controversial, because the name dolomite was first applied to the rock during the late 18th century and thus has technical precedence. The use of

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2436-492: The mixing zone serves as domain of intense microbial activity which promotes dolomitization. A third model postulates that normal seawater is the dolomitizing fluid, and the necessary large volumes are flushed through the dolomitizing limestone through tidal pumping. Dolomite formation at Sugarloaf Key , Florida, may be an example of this process. A similar process might occur during rises in sea level, as large volumes of water move through limestone platform rock. Regardless of

2494-579: The most authoritative study of the mountain range, said that this announcement was the culmination of a campaign that began in 2006. "I'm most grateful there is now international recognition of this great mountain range that has witnessed the whole span of life, from its very origins," he said. "The Magaliesberg is almost 100 times older than Mount Everest and half the age of the earth , a unique treasure for us in this part of Africa." The Magaliesberg mountains offer excellent rock climbing opportunities, spread across its many kloofs and escarpments. The climbing

2552-515: The mountain, but almost never on the northern slopes. The area around the Magaliesberg range has seen extremely lengthy occupation by humans dating back at least 2 million years to the earliest hominin species (such as Mrs Ples ) in and around the Sterkfontein Caves, which lie at the Cradle of Humankind World Heritage Site , close to the town of Magaliesburg . The earliest known name for

2610-427: The pore space in the dolomitizing limestone. Several processes have been proposed for dolomitization. The hypersaline model (also known as the evaporative reflux model ) is based on the observation that dolomite is very commonly found in association with limestone and evaporites , with the limestone often interbedded with the dolomite. According to this model, dolomitization takes place in a closed basin where seawater

2668-401: The process remains poorly understood. There are also fine-grained dolomites showing no textural indications that they formed by replacement, and it is uncertain whether they formed by replacement of limestone that left no textural traces or are true primary dolomites. This dolomite problem was first recognized over two centuries ago but is still not fully resolved. The dolomitization reaction

2726-483: The purpose of forming hunting parties to gather ivory and other products from further north. Subsequently the Boers began settling in the valleys of the Magaliesberg Range and in the Bushveld north of the Magaliesberg, and turned the region into some of the most productive farmland in South Africa, while displacing their former allies, confining them to locations and reserves. The area saw some heavy fighting during

2784-456: The question of whether this can lead to precipitation of dolomite. Dolomitization can sometimes be reversed, and a dolomite bed converted back to limestone. This is indicated by a texture of pseudomorphs of mineral dolomite that have been replaced with calcite. Dedolomitized limestone is typically associated with gypsum or oxidized pyrite , and dedolomitization is thought to occur at very shallow depths through infiltration of surface water with

2842-614: The re-conquest of the region was a cooperative venture of the Boers and the Sotho-Tswana against the Matabele, the Boers and Sotho-Tswana had friendly relations at the beginning of white settlement . These friendly relations are reflected in the name of the main Boer town, Rustenburg ( lit . resting town), because it seemed to them that they would not have to engage in any more fighting against African communities. The Boers initially settled south of

2900-528: The region include: 24°S 28°E  /  24°S 28°E  / -24; 28 Magaliesberg The Magaliesberg (historically also known as Macalisberg or Cashan Mountains ) of northern South Africa , is a modest but well-defined mountain range composed mainly of quartzites. It rises at a point south of the Pilanesberg (and the Pilanesberg National Park ) to form

2958-424: The region tends to be dry, the Bushveld is mostly beef cattle and game farming country, with only a few drought-resistant crops such as sorghum and millet being farmed, usually under irrigation . The term Middleveld is sometimes used to describe land lying between an elevation of 600 and 1,200 m (2,000 and 3,900 ft) and has been treated as synonymous with the term Bushveld . Towns and cities in

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3016-400: The sulfate concentration. With time other pathways of interaction between microbial activity and dolomite formation have been added to the discord regarding their role in modulation and generation of polysaccharides , manganese and zinc within the porewater. Meanwhile, a contrary view held by other researchers is that microorganisms precipitate only high-magnesium calcite but leave open

3074-422: The surrounding matrix composed of dolomite grains. Sometimes dolomite rhombs are seen cut across the fossil outline. However, some dolomite shows no textural indications that it was formed by replacement of limestone. Dolomite is widespread in its occurrences, though not as common as limestone. It is typically found in association with limestone or evaporite beds and is often interbedded with limestone. There

3132-526: The term dolostone was not recommended by the Glossary of Geology published by the American Geological Institute . In old USGS publications, dolomite was referred to as magnesian limestone , a term now reserved for magnesium -deficient dolomites or magnesium-rich limestones. Dolomite rock is defined as sedimentary carbonate rock composed of more than 50% mineral dolomite . Dolomite

3190-653: The unique nature of the Magaliesberg and the powerful contribution it is making to our country, to the ecosystem services in Gauteng and the North West and the communities it nurtures over an extensive area," said Paul Fatti, chair of the Magaliesberg Biosphere Initiative Group (MBIG) that has been lobbying authorities since 2007 to support the establishment of the biosphere. Vincent Carruthers, past chair of MBIG and renowned author of The Magaliesberg ,

3248-626: Was formed as a magnesium replacement of limestone or of lime mud before lithification . The geological process of conversion of calcite to dolomite is known as dolomitization and any intermediate product is known as dolomitic limestone . The "dolomite problem" refers to the vast worldwide depositions of dolomite in the past geologic record in contrast to the limited amounts of dolomite formed in modern times. Recent research has revealed sulfate-reducing bacteria living in anoxic conditions precipitate dolomite which indicates that some past dolomite deposits may be due to microbial activity. Dolomite

3306-446: Was of great importance to both the Boer and the British forces, especially the two routes between Pretoria and Rustenburg, which crossed it at Silkaatsnek and Kommandonek, respectively. As a result, many battles, such as the battles of Buffelspoort, Nooitgedacht and Olifantsnek were fought in the area. After the war, farms in the area were reoccupied and farming was resumed, tobacco and citrus being particularly successful. In 1923

3364-409: Was subsequently eroded so that it only remains along the Transvaal Basin's southern rim. The range forms a natural barrier between the lower lying Bushveld to the north and the cooler Highveld to the south. The range receives rainfall in summer in the form of thunderstorms, with an average of 650 mm (26 in) annually. In winter, frost occurs frequently in the valleys on the southern side of

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