Bornhardt
Encyclopedia
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
s or gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
es, though occasionally formed in other rock types such as dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
, norite
Norite
Norite is a mafic intrusive igneous rock composed largely of the calcium-rich plagioclase labradorite and hypersthene with olivine. Norite is essentially indistinguishable from gabbro without thin section study under the petrographic microscope...
, limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
, sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
and conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
. Uluru
Uluru
Uluru , also known as Ayers Rock, is a large sandstone rock formation in the southern part of the Northern Territory, central Australia. It lies south west of the nearest large town, Alice Springs; by road. Kata Tjuta and Uluru are the two major features of the Uluṟu-Kata Tjuṯa National Park....
, in Central Australia, is mainly composed of sandstones, while the nearby Kata Tjuta
Kata Tjuta
Kata Tjuta, sometimes written Tjuṯa , and also known as Mount Olga , are a group of large domed rock formations or bornhardts located about southwest of Alice Springs, in the southern part of the Northern Territory, central Australia...
is composed of conglomerates. They are named after Wilhelm Bornhardt
Friedrich Wilhelm Conrad Eduard Bornhardt
Friedrich Wilhelm Conrad Eduard Bornhardt was a German geologist, engineer and explorer, and was Director of the Berlin College of Mines from 1907 to 1916....
(1864–1946), a German geologist and explorer of German East Africa
German East Africa
German East Africa was a German colony in East Africa, which included what are now :Burundi, :Rwanda and Tanganyika . Its area was , nearly three times the size of Germany today....
, who first described the feature. The Sugar Loaf Mountain of Rio de Janeiro
Rio de Janeiro
Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...
is a typical example of this landform and is the origin of the common bornhardt nickname "sugar loaf".
Bornhardts are seen at their best in arid and semi-arid regions, but occur over a wide range of climates. Found in diverse topographic settings they mainly occur in multicyclic landscapes. They give rise to other types of inselberg, such as nubbins (or knoll
Hillock
A hillock or knoll is a small hill, usually separated from a larger group of hills such as a range. Hillocks are similar in their distribution and size to small mesas or buttes. The term is largely a British one...
s) and castle koppies.
Depending on their shape they are known as sugar loaves, whalebacks, turtlebacks or simply domes. They are locally known as dwalas, half-oranges, matopos, morros, etc. Often, the underlying geological fracture pattern is shown by the surface arrangement of bornhardts, as can be seen in the Kamiesberge
Kamiesberge
The Kamiesberge , is a mountain range of jumbled granite inselbergs or bornhardts dotted over sandy plains and centered around Kamieskroon in Namaqualand in South Africa. In appearance the range is very like the Matopos of Zimbabwe...
of Namaqualand
Namaqualand
Namaqualand is an arid region of Namibia and South Africa, extending along the west coast over and covering a total area of 170,000 square miles/440,000 km². It is divided by the lower course of the Orange River into two portions - Little Namaqualand to the south and Great Namaqualand to the...
and the Everard Ranges
Everard Ranges
The Everard Ranges are ranges of low rounded granite hills, of Palaeocene origin between 20 and 60 million years ago, in Central Australia and located 80 km west of Mintabie...
of Central Australia
Central Australia
Central Australia/Alice Springs Region is one of the five regions in the Northern Territory. The term Central Australia is used to describe an area centred on Alice Springs in Australia. It is sometimes referred to as Centralia; likewise the people of the area are sometimes called Centralians...
.