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84-782: The Afar Triangle , the northern part of which is the Danakil Depression , is part of the Great Rift Valley of Ethiopia , and is located in the north of the region. It has the lowest point in Ethiopia and one of the lowest in Africa. The southern part of the region consists of the valley of the Awash River , which empties into a string of lakes along the Djibouti–Ethiopia border . Other notable landmarks include

168-712: A volcanic eruption occurred within the Afar rift at the Dabbahu and Erta Ale volcanoes. Some 2.5 cubic kilometers of molten rock was injected from below into the plate along a dyke between depths of 2 and 9 km (1 and 6 mi), forcing open an 8 m (26 ft) wide gap on the surface, known as the Dabbahu fissure . Related eruptions have taken place in Teru and Aura woredas . The rift has recently been recorded by means of three-dimensional laser mapping. The region's salt deposits were created over time as water from

252-684: A 60 kilometres (37 mi) long, 8 metres (26 ft) wide dike within days. The Afar Depression , a plate tectonic triple junction, is found in the Afar Regional State. This geologic feature is one of Earth's great active volcanic areas. Due to this volcanic activity the floor of the depression is composed of lava, mostly basalt. The continuous process of volcanism results in the occurrence of major minerals , including potash , sulfur , salt , bentonite and gypsum . In addition to these minerals, there are also promising geothermal energy sources and hot springs in different areas of

336-585: A bend in the middle that is caused by start of the twin. Penetration twins consist of two single crystals that have grown into each other; examples of this twinning include cross-shaped staurolite twins and Carlsbad twinning in orthoclase. Cyclic twins are caused by repeated twinning around a rotation axis. This type of twinning occurs around three, four, five, six, or eight-fold axes, and the corresponding patterns are called threelings, fourlings, fivelings , sixlings, and eightlings. Sixlings are common in aragonite. Polysynthetic twins are similar to cyclic twins through

420-417: A bigger coordination numbers because of the increase in relative size as compared to oxygen (the last orbital subshell of heavier atoms is different too). Changes in coordination numbers leads to physical and mineralogical differences; for example, at high pressure, such as in the mantle , many minerals, especially silicates such as olivine and garnet , will change to a perovskite structure , where silicon

504-416: A definite crystalline structure, such as opal or obsidian , are more properly called mineraloids . If a chemical compound occurs naturally with different crystal structures, each structure is considered a different mineral species. Thus, for example, quartz and stishovite are two different minerals consisting of the same compound, silicon dioxide . The International Mineralogical Association (IMA)

588-473: A distinct mineral: The details of these rules are somewhat controversial. For instance, there have been several recent proposals to classify amorphous substances as minerals, but they have not been accepted by the IMA. The IMA is also reluctant to accept minerals that occur naturally only in the form of nanoparticles a few hundred atoms across, but has not defined a minimum crystal size. Some authors require

672-698: A giant rift was formed in just a few days. The rift opened when the Dabbahu Volcano , situated in the north of the region, erupted. The crack forming is thought to be part of the process in which the Arabian Plate , the Nubian Plate, and the Somali Plate, are moving apart. This new crack, 500 metres (1,640 ft) long, and 60 metres (197 ft) deep, opened when the lava from the erupting volcano flowed underground and cooled forming

756-500: A hominid jawbone in the Ledi-Geraru region of Afar. Scientists estimated that the fossil dates to around 2.8 million years ago, which is 400,000 years before the next oldest hominid fossil remains. In 2015, a hominin jawbone and teeth was discovered in the Afar region. Scientists believe that the bones belonged to a previously undiscovered ancestor. The new species was named Australopithecus deyiremeda , meaning "close relative" in

840-466: A household, with urban households having on average 4 and rural households 6 people. Religion in Afar Region (2007) In the previous census, conducted in 1994, the region's population was reported to be 1,106,383 of which 626,839 were men and 479,544 women; urban inhabitants were 85,879 or 7.76% of the population. Afar is predominantly (89.96%) spoken in the region and is the working language of

924-463: A key to defining a substance as a mineral. A 2011 article defined icosahedrite , an aluminium-iron-copper alloy, as a mineral; named for its unique natural icosahedral symmetry , it is a quasicrystal . Unlike a true crystal, quasicrystals are ordered but not periodic. A rock is an aggregate of one or more minerals or mineraloids. Some rocks, such as limestone or quartzite , are composed primarily of one mineral – calcite or aragonite in

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1008-409: A mineral defines how much it can resist scratching or indentation. This physical property is controlled by the chemical composition and crystalline structure of a mineral. The most commonly used scale of measurement is the ordinal Mohs hardness scale, which measures resistance to scratching. Defined by ten indicators, a mineral with a higher index scratches those below it. The scale ranges from talc,

1092-622: A new ocean basin as large as today's Red Sea, and separating the Somali plate and the Horn of Africa from the rest of the continent. The floor of the Afar Depression is composed of lava , mostly basalt . One of Earth's five lava lakes , Erta Ale is found here, as well as Dabbahu Volcano. It has been proposed that the Afar Depression is underlain by a mantle plume , a great upwelling of mantle that melts to yield basalt as it approaches

1176-478: A population of 1,390,273, consisting of 775,117 men and 615,156 women; urban inhabitants number 185,135 or 13.32% of the population, a further 409,123 or 29.43% were pastoralists . With an estimated area of 96,707 square kilometers, this region has an estimated density of 14.38 people per square kilometer. For the entire region 247,255 households were counted, which results in an average for the Region of 5.6 persons to

1260-432: A sedimentary mineral, and silicic acid ): Under low-grade metamorphic conditions, kaolinite reacts with quartz to form pyrophyllite (Al 2 Si 4 O 10 (OH) 2 ): As metamorphic grade increases, the pyrophyllite reacts to form kyanite and quartz: Alternatively, a mineral may change its crystal structure as a consequence of changes in temperature and pressure without reacting. For example, quartz will change into

1344-573: A skeleton, which dates to around 4.4 million years ago. Named Ardi , it is a form of the species Ardipithecus ramidus . The specimen is a distant cousin of the Australopithecus afarensis , Lucy's species. In June 2010, the oldest direct evidence of stone tool manufacture was found in the Afar region and attributed to Australopithecus afarensis . In 2013, a graduate student from the Arizona State University discovered

1428-406: A tetrahedral fashion; on the other hand, graphite is composed of sheets of carbons in sp hybrid orbitals, where each carbon is bonded covalently to only three others. These sheets are held together by much weaker van der Waals forces , and this discrepancy translates to large macroscopic differences. Twinning is the intergrowth of two or more crystals of a single mineral species. The geometry of

1512-935: A variety of its SiO 2 polymorphs , such as tridymite and cristobalite at high temperatures, and coesite at high pressures. Classifying minerals ranges from simple to difficult. A mineral can be identified by several physical properties, some of them being sufficient for full identification without equivocation. In other cases, minerals can only be classified by more complex optical , chemical or X-ray diffraction analysis; these methods, however, can be costly and time-consuming. Physical properties applied for classification include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, cleavage and fracture, and specific gravity. Other less general tests include fluorescence , phosphorescence , magnetism , radioactivity , tenacity (response to mechanical induced changes of shape or form), piezoelectricity and reactivity to dilute acids . Crystal structure results from

1596-502: A variety of minerals because of the need to balance charges. Because the eight most common elements make up over 98% of the Earth's crust, the small quantities of the other elements that are typically present are substituted into the common rock-forming minerals. The distinctive minerals of most elements are quite rare, being found only where these elements have been concentrated by geological processes, such as hydrothermal circulation , to

1680-595: A white mica, can be used for windows (sometimes referred to as isinglass), as a filler, or as an insulator. Ores are minerals that have a high concentration of a certain element, typically a metal. Examples are cinnabar (HgS), an ore of mercury; sphalerite (ZnS), an ore of zinc; cassiterite (SnO 2 ), an ore of tin; and colemanite , an ore of boron . Gems are minerals with an ornamental value, and are distinguished from non-gems by their beauty, durability, and usually, rarity. There are about 20 mineral species that qualify as gem minerals, which constitute about 35 of

1764-591: A zone). Haruka District 11°49′N 41°25′E  /  11.817°N 41.417°E  / 11.817; 41.417 Afar Triangle The Afar Triangle (also called the Afar Depression ) is a geological depression caused by the Afar triple junction , which is part of the Great Rift Valley in East Africa . The region has disclosed fossil specimens of the very earliest hominins ; that is,

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1848-429: Is a purple variety of the mineral species quartz . Some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure; for example, the formula of mackinawite is given as (Fe,Ni) 9 S 8 , meaning Fe x Ni 9- x S 8 , where x is a variable number between 0 and 9. Sometimes a mineral with variable composition

1932-707: Is a sedimentary rock composed primarily of organically derived carbon. In rocks, some mineral species and groups are much more abundant than others; these are termed the rock-forming minerals. The major examples of these are quartz, the feldspars , the micas , the amphiboles , the pyroxenes , the olivines , and calcite; except for the last one, all of these minerals are silicates. Overall, around 150 minerals are considered particularly important, whether in terms of their abundance or aesthetic value in terms of collecting. Commercially valuable minerals and rocks, other than gemstones, metal ores, or mineral fuels, are referred to as industrial minerals . For example, muscovite ,

2016-414: Is covered by salt deposits, and mining salt is a major source of income for many Afar groups. The Afar Depression biome is characterized as desert scrubland . Vegetation is mostly confined to drought-resistant plants such as small trees (e.g. species of the dragon tree ), shrubs, and grasses. Wildlife includes many herbivores such as Grévy's zebra , Soemmerring's gazelle , beisa and, notably,

2100-448: Is in octahedral coordination. Other examples are the aluminosilicates kyanite , andalusite , and sillimanite (polymorphs, since they share the formula Al 2 SiO 5 ), which differ by the coordination number of the Al ; these minerals transition from one another as a response to changes in pressure and temperature. In the case of silicate materials, the substitution of Si by Al allows for

2184-408: Is possible for one element to be substituted for another. Chemical substitution will occur between ions of a similar size and charge; for example, K will not substitute for Si because of chemical and structural incompatibilities caused by a big difference in size and charge. A common example of chemical substitution is that of Si by Al , which are close in charge, size, and abundance in the crust. In

2268-470: Is possible for two rocks to have an identical or a very similar bulk rock chemistry without having a similar mineralogy. This process of mineralogical alteration is related to the rock cycle . An example of a series of mineral reactions is illustrated as follows. Orthoclase feldspar (KAlSi 3 O 8 ) is a mineral commonly found in granite , a plutonic igneous rock . When exposed to weathering, it reacts to form kaolinite (Al 2 Si 2 O 5 (OH) 4 ,

2352-653: Is split into separate species, more or less arbitrarily, forming a mineral group ; that is the case of the silicates Ca x Mg y Fe 2- x - y SiO 4 , the olivine group . Besides the essential chemical composition and crystal structure, the description of a mineral species usually includes its common physical properties such as habit , hardness , lustre , diaphaneity , colour, streak , tenacity , cleavage , fracture , parting, specific gravity , magnetism , fluorescence , radioactivity , as well as its taste or smell and its reaction to acid . Minerals are classified by key chemical constituents;

2436-524: Is the angle opposite the a-axis, viz. the angle between the b and c axes): The hexagonal crystal family is also split into two crystal systems  – the trigonal , which has a three-fold axis of symmetry, and the hexagonal, which has a six-fold axis of symmetry. Chemistry and crystal structure together define a mineral. With a restriction to 32 point groups, minerals of different chemistry may have identical crystal structure. For example, halite (NaCl), galena (PbS), and periclase (MgO) all belong to

2520-422: Is the generally recognized standard body for the definition and nomenclature of mineral species. As of November 2024 , the IMA recognizes 6,100 official mineral species. The chemical composition of a named mineral species may vary somewhat due to the inclusion of small amounts of impurities. Specific varieties of a species sometimes have conventional or official names of their own. For example, amethyst

2604-405: Is the hardest natural substance, has an adamantine lustre, and belongs to the isometric crystal family, whereas graphite is very soft, has a greasy lustre, and crystallises in the hexagonal family. This difference is accounted for by differences in bonding. In diamond, the carbons are in sp hybrid orbitals, which means they form a framework where each carbon is covalently bonded to four neighbours in

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2688-456: Is typical of garnet, prismatic (elongated in one direction), and tabular, which differs from bladed habit in that the former is platy whereas the latter has a defined elongation. Related to crystal form, the quality of crystal faces is diagnostic of some minerals, especially with a petrographic microscope. Euhedral crystals have a defined external shape, while anhedral crystals do not; those intermediate forms are termed subhedral. The hardness of

2772-573: The Awash National Park . Based on the 2017 projections by the Central Statistical Agency of Ethiopia (CSA), the Afar Regional State has a population of 1,812,002, consisting of 991,000 men and 821,002 women; urban inhabitants number 346,000 of the population, a further 1,466,000 were pastoralists. Based on the 2007 Census conducted by the Central Statistical Agency of Ethiopia (CSA), the Afar Regional State has

2856-618: The CIPW norm , which gives reasonable estimates for volcanic rock formed from dry magma. The chemical composition may vary between end member species of a solid solution series. For example, the plagioclase feldspars comprise a continuous series from sodium -rich end member albite (NaAlSi 3 O 8 ) to calcium -rich anorthite (CaAl 2 Si 2 O 8 ) with four recognized intermediate varieties between them (given in order from sodium- to calcium-rich): oligoclase , andesine , labradorite , and bytownite . Other examples of series include

2940-670: The Cleveland Museum of Natural History . On March 5, 2005, another skeleton, estimated to be 3.8 million years old and said to be the world's oldest bipedal hominid skeleton , was found in the region. Yohannes Haile-Selassie led digs there each year from 2004 to 2007. On March 24, 2006, it was reported that a "significantly complete" cranium had been found at Gawis in the Gona area. The cranium appears as an intermediate form between Homo erectus and Homo sapiens . On October 1, 2009, scientists reported that they had found

3024-508: The Eritrean–Ethiopian War of 1998 to 2000. On January 18, 2012, five foreign tourists were murdered while on holiday in the region. The Ethiopian government has accused Eritrean gunmen of being responsible for the attack. Many governments around the world advise against traveling to the Afar region, citing increasing security concerns. Additionally, this region is also a hub for Afar–Somali clashes , due to many kebeles being put into

3108-517: The Middle Awash region and numerous prehistoric sites of fossil hominin discoveries, including: the hominids and possible hominins, Ardi , or Ardipithecus ramidus , and Ardipithecus kadabba , see below; the Gawis cranium hominin from Gona ; several sites of the world's oldest stone tools; Hadar , the site of Lucy , the fossilized specimen of Australopithecus afarensis ; and Dikika ,

3192-496: The hydrosphere , atmosphere , and biosphere . The group's scope includes mineral-forming microorganisms, which exist on nearly every rock, soil, and particle surface spanning the globe to depths of at least 1600 metres below the sea floor and 70 kilometres into the stratosphere (possibly entering the mesosphere ). Biogeochemical cycles have contributed to the formation of minerals for billions of years. Microorganisms can precipitate metals from solution , contributing to

3276-427: The standard of living for the Afar Regional State as of 2005 include the following: 67.3% of the inhabitants fall into the lowest wealth quintile; adult literacy for men is 27% and for women 15.6%; and the regional infant mortality rate is 61 infant deaths per 1,000 live births, which is less than the nationwide average of 77; at least half of these deaths occurred in the infants' first month of life. On 20 April 2007,

3360-455: The 78 mineral classes listed in the Dana classification scheme. Skinner's (2005) definition of a mineral takes this matter into account by stating that a mineral can be crystalline or amorphous. Although biominerals are not the most common form of minerals, they help to define the limits of what constitutes a mineral proper. Nickel's (1995) formal definition explicitly mentioned crystallinity as

3444-513: The Afar region by the government. These include key towns like Gadamaytu, Undufo and Adaytu where battles between the Afar region and Somali region militaries happen. These conflicts have had many losses, and have led to the south-eastern parts of the region being an unstable zone. Hadar , a community in Afar, was the site of the discovery in 1973–1974 of " Lucy ", the Australopithecus afarensis skeletal remains, by Donald Johanson of

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3528-640: The Danakil Depression is one of the hottest places year-round anywhere on Earth. There is no rain for most of the year; the yearly rainfall averages range from 100 to 200 mm (4 to 8 in), with even less rain falling closer to the coast. Daily mean temperatures at Dallol ranged from 30 °C (86 °F) in January to 39 °C (102 °F) in July in six years of observations from 1960 to 1966. The Awash River , flowing north-eastward through

3612-431: The IMA's decision to exclude biogenic crystalline substances. For example, Lowenstam (1981) stated that "organisms are capable of forming a diverse array of minerals, some of which cannot be formed inorganically in the biosphere." Skinner (2005) views all solids as potential minerals and includes biominerals in the mineral kingdom, which are those that are created by the metabolic activities of organisms. Skinner expanded

3696-455: The IMA. They are most commonly named after a person , followed by discovery location; names based on chemical composition or physical properties are the two other major groups of mineral name etymologies. Most names end in "-ite"; the exceptions are usually names that were well-established before the organization of mineralogy as a discipline, for example galena and diamond . A topic of contention among geologists and mineralogists has been

3780-556: The Latin species , "a particular sort, kind, or type with distinct look, or appearance". The abundance and diversity of minerals is controlled directly by their chemistry, in turn dependent on elemental abundances in the Earth. The majority of minerals observed are derived from the Earth's crust . Eight elements account for most of the key components of minerals, due to their abundance in the crust. These eight elements, summing to over 98% of

3864-546: The Red Sea periodically flooded the depression and evaporated; the most recent such flood was roughly 30,000 years ago. Over the next millions of years, geologists expect erosion and the Red Sea to breach the highlands surrounding the Afar Depression and flood the valley. Geologists predict that in about 10 million years the whole 6,000 km (3,700 mi) length of the East African Rift will be submerged, forming

3948-488: The aluminium abundance is unusually high, the excess aluminium will form muscovite or other aluminium-rich minerals. If silicon is deficient, part of the feldspar will be replaced by feldspathoid minerals. Precise predictions of which minerals will be present in a rock of a particular composition formed at a particular temperature and pressure requires complex thermodynamic calculations. However, approximate estimates may be made using relatively simple rules of thumb , such as

4032-504: The annual dry season, and ends as a chain of saline lakes . The northern part of the Afar Depression is also known as the Danakil Depression . The lowlands are affected by heat, drought , and minimal air circulation, and contain the hottest places (year-round average temperatures) of anywhere on Earth. The Afar Triangle is bordered as follows (see the topographic map): on the west by the Ethiopian Plateau and escarpment ; to

4116-461: The basis of a survey performed in December 2003 that nomadic inhabitants had 1,990,850 cattle (an 83.8% share of those animals in the region that year), 2,303,250 sheep (90.6%), 3,960,510 goats (90%), 759,750 camels (85.9%), 175,180 asses (92.5%), 2960 mules (88.6%), and 900 horses (100%). As of 2012, the area has been increasingly unstable, as tensions between Ethiopia and Eritrea remain high after

4200-449: The bulk chemistry of the parent body. For example, in most igneous rocks, the aluminium and alkali metals (sodium and potassium) that are present are primarily found in combination with oxygen, silicon, and calcium as feldspar minerals. However, if the rock is unusually rich in alkali metals, there will not be enough aluminium to combine with all the sodium as feldspar, and the excess sodium will form sodic amphiboles such as riebeckite . If

4284-424: The case of limestone, and quartz in the latter case. Other rocks can be defined by relative abundances of key (essential) minerals; a granite is defined by proportions of quartz, alkali feldspar , and plagioclase feldspar . The other minerals in the rock are termed accessory minerals , and do not greatly affect the bulk composition of the rock. Rocks can also be composed entirely of non-mineral material; coal

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4368-415: The coordination of the silicate is by a number: in the case of the silica tetrahedron, the silicon is said to have a coordination number of 4. Various cations have a specific range of possible coordination numbers; for silicon, it is almost always 4, except for very high-pressure minerals where the compound is compressed such that silicon is in six-fold (octahedral) coordination with oxygen. Bigger cations have

4452-417: The crust by weight, are, in order of decreasing abundance: oxygen , silicon , aluminium , iron , magnesium , calcium , sodium and potassium . Oxygen and silicon are by far the two most important – oxygen composes 47% of the crust by weight, and silicon accounts for 28%. The minerals that form are those that are most stable at the temperature and pressure of formation, within the limits imposed by

4536-434: The difference in charge has to accounted for by making a second substitution of Si by Al . Coordination polyhedra are geometric representations of how a cation is surrounded by an anion. In mineralogy, coordination polyhedra are usually considered in terms of oxygen, due its abundance in the crust. The base unit of silicate minerals is the silica tetrahedron – one Si surrounded by four O . An alternate way of describing

4620-414: The dipyramidal point group. These differences arise corresponding to how aluminium is coordinated within the crystal structure. In all minerals, one aluminium ion is always in six-fold coordination with oxygen. Silicon, as a general rule, is in four-fold coordination in all minerals; an exception is a case like stishovite (SiO 2 , an ultra-high pressure quartz polymorph with rutile structure). In kyanite,

4704-477: The earliest of the human clade, and it is thought by some paleontologists to be the cradle of the evolution of humans. The Depression overlaps the borders of Eritrea , Djibouti and the entire Afar Region of Ethiopia ; and it contains the lowest point in Africa , Lake Assal , Djibouti , at 155 m (509 ft) below sea level. The Awash River is the main waterflow into the region, but it runs dry during

4788-584: The event. The Afar Depression is the product of a tectonic triple-rifts junction (the Afar triple junction), where the spreading ridges forming the Red Sea and the Gulf of Aden emerge on land and meet the East African Rift . The conjunction of these three plates of Earth's crust is near Lake Abbe . The Afar Depression is one of two places on Earth where a mid-ocean ridge can be studied on land,

4872-517: The example of plagioclase, there are three cases of substitution. Feldspars are all framework silicates, which have a silicon-oxygen ratio of 2:1, and the space for other elements is given by the substitution of Si by Al to give a base unit of [AlSi 3 O 8 ] ; without the substitution, the formula would be charge-balanced as SiO 2 , giving quartz. The significance of this structural property will be explained further by coordination polyhedra. The second substitution occurs between Na and Ca ; however,

4956-778: The formation of ore deposits. They can also catalyze the dissolution of minerals. Prior to the International Mineralogical Association's listing, over 60 biominerals had been discovered, named, and published. These minerals (a sub-set tabulated in Lowenstam (1981) ) are considered minerals proper according to Skinner's (2005) definition. These biominerals are not listed in the International Mineral Association official list of mineral names; however, many of these biomineral representatives are distributed amongst

5040-410: The generic AX 2 formula; these two groups are collectively known as the pyrite and marcasite groups. Polymorphism can extend beyond pure symmetry content. The aluminosilicates are a group of three minerals – kyanite , andalusite , and sillimanite  – which share the chemical formula Al 2 SiO 5 . Kyanite is triclinic, while andalusite and sillimanite are both orthorhombic and belong to

5124-451: The hexaoctahedral point group (isometric family), as they have a similar stoichiometry between their different constituent elements. In contrast, polymorphs are groupings of minerals that share a chemical formula but have a different structure. For example, pyrite and marcasite , both iron sulfides, have the formula FeS 2 ; however, the former is isometric while the latter is orthorhombic. This polymorphism extends to other sulfides with

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5208-522: The last viable population of African wild ass ( Equus africanus somalicus ). Birds include the ostrich , the endemic Archer's lark , the secretary bird , Arabian and Kori bustards , Abyssinian roller , and crested francolin . In the southern part of the plain lies the Mille-Serdo Wildlife Reserve . The Afar Triangle is a cradle source of the earliest hominins . It contains a paleo-archaeological district that includes

5292-461: The material to be a stable or metastable solid at room temperature (25 °C). However, the IMA only requires that the substance be stable enough for its structure and composition to be well-determined. For example, it has recently recognized meridianiite (a naturally occurring hydrate of magnesium sulfate ) as a mineral, even though it is formed and stable only below 2 °C. As of November 2024 , 6,100 mineral species are approved by

5376-494: The most common gemstones. Gem minerals are often present in several varieties, and so one mineral can account for several different gemstones; for example, ruby and sapphire are both corundum , Al 2 O 3 . The first known use of the word "mineral" in the English language ( Middle English ) was the 15th century. The word came from Medieval Latin : minerale , from minera , mine, ore. The word "species" comes from

5460-428: The most encompassing of these being the six crystal families. These families can be described by the relative lengths of the three crystallographic axes, and the angles between them; these relationships correspond to the symmetry operations that define the narrower point groups. They are summarized below; a, b, and c represent the axes, and α, β, γ represent the angle opposite the respective crystallographic axis (e.g. α

5544-400: The native Afar language. The species lived around 3.5–3.3 million years ago, about the same time period as other hominins such as Australopithecus afarensis . Source: Like other regions in Ethiopia, Afar Region is subdivided into administrative zones , in case of Afar, into six zones (and one special woreda , an administrative subdivision which is an autonomous area and is not part of

5628-808: The north-east (between it and the Red Sea) by the Danakil block ; to the south by the Somali Plateau and escarpment; and to the south-east by the Ali-Sabieh block (adjoining the Somali Plateau). Many important fossil localities exist in the Afar region, including the Middle Awash region and the sites of Hadar , Dikika , and Woranso-Mille. These sites have produced specimens of the earliest (fossil) hominins and of human tool culture, as well as many fossils of various flora and fauna. Dallol in

5712-402: The olivine series of magnesium-rich forsterite and iron-rich fayalite, and the wolframite series of manganese -rich hübnerite and iron-rich ferberite . Chemical substitution and coordination polyhedra explain this common feature of minerals. In nature, minerals are not pure substances, and are contaminated by whatever other elements are present in the given chemical system. As a result, it

5796-622: The orderly geometric spatial arrangement of atoms in the internal structure of a mineral. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic and can be determined by X-ray diffraction. Minerals are typically described by their symmetry content. Crystals are restricted to 32 point groups , which differ by their symmetry. These groups are classified in turn into more broad categories,

5880-501: The other being Iceland . Within the triangle, the Earth's crust is slowly rifting apart at a rate of 1–2 cm (0.4–0.8 in) per year along each of the three rift zones forming the "legs" of the triple junction. The immediate consequences are recurring sequences of earthquakes with deep fissures in the terrain hundreds of metres long, and the valley floor sinking broadly across the depression. During September and October 2005 some 163 earthquakes of magnitudes greater than 3.9 and

5964-563: The point where they can no longer be accommodated in common minerals. Changes in temperature and pressure and composition alter the mineralogy of a rock sample. Changes in composition can be caused by processes such as weathering or metasomatism ( hydrothermal alteration ). Changes in temperature and pressure occur when the host rock undergoes tectonic or magmatic movement into differing physical regimes. Changes in thermodynamic conditions make it favourable for mineral assemblages to react with each other to produce new minerals; as such, it

6048-447: The presence of repetitive twinning; however, instead of occurring around a rotational axis, polysynthetic twinning occurs along parallel planes, usually on a microscopic scale. Crystal habit refers to the overall shape of crystal. Several terms are used to describe this property. Common habits include acicular, which describes needlelike crystals as in natrolite , bladed, dendritic (tree-pattern, common in native copper ), equant, which

6132-568: The previous definition of a mineral to classify "element or compound, amorphous or crystalline, formed through biogeochemical processes," as a mineral. Recent advances in high-resolution genetics and X-ray absorption spectroscopy are providing revelations on the biogeochemical relations between microorganisms and minerals that may shed new light on this question. For example, the IMA-commissioned "Working Group on Environmental Mineralogy and Geochemistry " deals with minerals in

6216-499: The region's national parks. Because the region's tourism development is still in a poor state there are only two lodges in Awash National Park . The CSA estimated in 2005 that farmers in the Afar Regional State had a total of 327,370 cattle (representing 0.84% of Ethiopia's total cattle), 196,390 sheep (1.13%), 483,780 goats (3.73%), 200 mules (0.14%), 12,270 asses (0.49%), 99,830 camels (21.85%), 38,320 poultry of all species (0.12%), and 810 beehives (less than 0.1%). The CSA estimated on

6300-624: The region. Most of the region's mineral potential are found in Dallol , Berhale and Afdera woredas of Zone Two. Elidar , Dubti and Millee in Zone One, and Gewane in Zone Three, also have some mineral possibilities. Afar is home to peculiar wildlife, which notably include the African wild ass , Grevy's zebra , wild fox, wild cat, cheetah, and ostrich. These wild animals are found in

6384-456: The regional government announced that it had increased health coverage from 34% to 40%, the result of construction of 64 new health clinics, increasing the total for the region to 111. Afar Depression , Erta Ale active volcano, Awash National Park , Yangudi Rassa National Park , Hadar and Aramis areas, are the major tourist attraction area of the region. The hot springs, Afar culture and cultural games are other attraction areas. In 2005,

6468-485: The second aluminium is in six-fold coordination; its chemical formula can be expressed as Al Al SiO 5 , to reflect its crystal structure. Andalusite has the second aluminium in five-fold coordination (Al Al SiO 5 ) and sillimanite has it in four-fold coordination (Al Al SiO 5 ). Differences in crystal structure and chemistry greatly influence other physical properties of the mineral. The carbon allotropes diamond and graphite have vastly different properties; diamond

6552-505: The sense of chemistry (such as mellite ). Moreover, living organisms often synthesize inorganic minerals (such as hydroxylapatite ) that also occur in rocks. The concept of mineral is distinct from rock , which is any bulk solid geologic material that is relatively homogeneous at a large enough scale. A rock may consist of one type of mineral or may be an aggregate of two or more different types of minerals, spacially segregated into distinct phases . Some natural solid substances without

6636-468: The site of the fossilized child Selam , an australopithecine hominin. In 1994, near the Awash River in Ethiopia, Tim D. White found the then-oldest known human ancestor: 4.4 million-year-old Ar. ramidus . A fossilized almost complete skeleton of a female hominin which he named " Ardi ", it took nearly 15 years to safely excavate, preserve, and describe the specimen and to prepare publication of

6720-579: The southern part of the Afar Region, provides a narrow green belt which enables life for the flora and fauna in the area and for the Afars , the nomadic people living in the Danakil Desert . About 128 kilometres (80 mi) from the Red Sea the Awash ends in a chain of salt lakes, where its waterflow evaporates as quickly as it is supplied. Some 1,200 km (460 sq mi) of the Afar Depression

6804-448: The state. Other languages with a significant number of speakers in the state include Amharic (6.83%), Tigrinnya (1.06%), Argobba (0.79%), Wolaitta (0.43%), and Oromifa (0.4%). According to the CSA, as of 2004, 48.57% of the total population had access to safe drinking water , of whom 26.89% were rural inhabitants and 78.11% were urban. Values for other reported common indicators of

6888-551: The surface. 11°30′N 41°00′E  /  11.5°N 41.0°E  / 11.5; 41.0 Minerals In geology and mineralogy , a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form. The geological definition of mineral normally excludes compounds that occur only in living organisms. However, some minerals are often biogenic (such as calcite ) or organic compounds in

6972-439: The twinning is controlled by the mineral's symmetry. As a result, there are several types of twins, including contact twins, reticulated twins, geniculated twins, penetration twins, cyclic twins, and polysynthetic twins. Contact, or simple twins, consist of two crystals joined at a plane; this type of twinning is common in spinel. Reticulated twins, common in rutile, are interlocking crystals resembling netting. Geniculated twins have

7056-472: The two dominant systems are the Dana classification and the Strunz classification. Silicate minerals comprise approximately 90% of the Earth's crust . Other important mineral groups include the native elements , sulfides , oxides , halides , carbonates , sulfates , and phosphates . The International Mineralogical Association has established the following requirements for a substance to be considered

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