Democratic Republic of the Congo
The Democratic Republic of the Congo known as DR Congo, the DRC, DROC, Congo-Kinshasa, or the Congo, is a country located in Central Africa. It is sometimes anachronistically referred to by its former name of Zaire, its official name between 1971 and 1997, it is, by area, the largest country in Sub-Saharan Africa, the second-largest in all of Africa, the 11th-largest in the world. With a population of over 78 million, the Democratic Republic of the Congo is the most populated Francophone country, the fourth-most-populated country in Africa, the 16th-most-populated country in the world. Eastern DR Congo is the scene of ongoing military conflict in Kivu, since 2015. Centred on the Congo Basin, the territory of the DRC was first inhabited by Central African foragers around 90,000 years ago and was reached by the Bantu expansion about 3,000 years ago. In the west, the Kingdom of Kongo ruled around the mouth of the Congo River from the 14th to 19th centuries. In the centre and east, the kingdoms of Luba and Lunda ruled from the 16th and 17th centuries to the 19th century.
In the 1870s, just before the onset of the Scramble for Africa, European exploration of the Congo Basin was carried out, first led by Henry Morton Stanley under the sponsorship of Leopold II of Belgium. Leopold formally acquired rights to the Congo territory at the Berlin Conference in 1885 and made the land his private property, naming it the Congo Free State. During the Free State, the colonial military unit, the Force Publique, forced the local population to produce rubber, from 1885 to 1908, millions of Congolese died as a consequence of disease and exploitation. In 1908, despite initial reluctance, formally annexed the Free State, which became the Belgian Congo; the Belgian Congo achieved independence on 30 June 1960 under the name Republic of the Congo. Congolese nationalist Patrice Lumumba was elected the first Prime Minister, while Joseph Kasa-Vubu became the first President. Conflict arose over the administration of the territory; the provinces of Katanga, under Moïse Tshombe, South Kasai attempted to secede.
After Lumumba turned to the Soviet Union for assistance in the crisis, the U. S. and Belgium became wary and oversaw his removal from office by Kasa-Vubu on 5 September and ultimate execution by Belgian-led Katangese troops on 17 January 1961. On 25 November 1965, Army Chief of Staff Joseph-Désiré Mobutu, who renamed himself Mobutu Sese Seko came into power through a coup d'état. In 1971, he renamed the country Zaire; the country was run as a dictatorial one-party state, with his Popular Movement of the Revolution as the sole legal party. Mobutu's government received considerable support from the United States, due to its anti-communist stance during the Cold War. By the early 1990s, Mobutu's government began to weaken. Destabilisation in the east resulting from the 1994 Rwandan genocide and disenfranchisement among the eastern Banyamulenge population led to a 1996 invasion led by Tutsi FPR-ruled Rwanda, which began the First Congo War. On 17 May 1997, Laurent-Désiré Kabila, a leader of Tutsi forces from the province of South Kivu, became President after Mobutu fled to Morocco, reverting the country's name to the Democratic Republic of the Congo.
Tensions between President Kabila and the Rwandan and Tutsi presence in the country led to the Second Congo War from 1998 to 2003. Nine African countries and around twenty armed groups became involved in the war, which resulted in the deaths of 5.4 million people. The two wars devastated the country. President Laurent-Désiré Kabila was assassinated by one of his bodyguards on 16 January 2001 and was succeeded eight days as President by his son Joseph; the Democratic Republic of the Congo is rich in natural resources but has had political instability, a lack of infrastructure, issues with corruption and centuries of both commercial and colonial extraction and exploitation with little holistic development. Besides the capital Kinshasa, the two next largest cities Lubumbashi and Mbuji-Mayi are both mining communities. DR Congo's largest export is raw minerals, with China accepting over 50% of DRC's exports in 2012. In 2016, DR Congo's level of human development was ranked 176th out of 187 countries by the Human Development Index.
As of 2018, around 600,000 Congolese have fled to neighbouring countries from conflicts in the centre and east of the DRC. Two million children risk starvation, the fighting has displaced 4.5 million people. The sovereign state is a member of the United Nations, Non-Aligned Movement, African Union, COMESA; the Democratic Republic of the Congo is named after the Congo River, which flows throughout the country. The Congo River is the world's second largest river by discharge; the Comité d'études du haut Congo, established by King Leopold II of Belgium in 1876, the International Association of the Congo, established by him in 1879, were named after the river. The Congo River itself was named by early European sailors after the Kingdom of Kongo and its Bantu inhabitants, the Kongo people, when they encountered them in the 16th century; the word Kongo comes from the Kongo language. According to American writer Samuel Henry Nelson "It is probable that the word'Kongo' itself implies a public gathering and that it is based on the root konga,'to gather'."
The modern name of the Kongo people, Bakongo was introduced in the early 20th century. The Democratic Republic of the Congo has been known in the past as, in chronological order, the Congo Free State, Belgian Congo, the Repub
Intrusive rock is formed when magma crystallizes and solidifies underground to form intrusions, for example plutons, dikes, sills and volcanic necks. Intrusive rock forms within Earth's crust from the crystallization of magma. Many mountain ranges, such as the Sierra Nevada in California, are formed from large granite intrusions. Intrusions are one of the two ways igneous rock. Technically an intrusion is any formation of intrusive igneous rock. In contrast, an extrusion consists of extrusive rock. Large bodies of magma that solidify underground before they reach the surface of the crust are called plutons. Plutonic rocks form 7% of the Earth's current land surface. Coarse-grained intrusive igneous rocks that form at depth within the earth are called abyssal while those that form near the surface are called subvolcanic or hypabyssal. Intrusive structures are classified according to whether or not they are parallel to the bedding planes or foliation of the country rock: if the intrusion is parallel the body is concordant, otherwise it is discordant.
An intrusive suite is a group of plutons related in time and space.. Intrusions vary from mountain-range-sized batholiths to thin veinlike fracture fillings of aplite or pegmatite. Intrusions can be classified according to the shape and size of the intrusive body and its relation to the other formations into which it intrudes: Batholith: a large irregular discordant intrusion Chonolith: an irregularly-shaped intrusion with a demonstrable base Cupola: a dome-shaped projection from the top of a large subterranean intrusion Dike: a narrow tabular discordant body nearly vertical Laccolith: concordant body with flat base and convex top with a feeder pipe below Lopolith: concordant body with flat top and a shallow convex base, may have a feeder dike or pipe below Phacolith: a concordant lens-shaped pluton that occupies the crest of an anticline or trough of a syncline Volcanic pipe or volcanic neck: tubular vertical body that may have been a feeder vent for a volcano Sill: a thin tabular concordant body intruded along bedding planes Stock: a smaller irregular discordant intrusive Boss: a small stock A body of intrusive igneous rock which crystallizes from magma cooling underneath the surface of the Earth is called a pluton.
If the pluton is large, it may be called a stock. Intrusive rocks are characterized by large crystal sizes, as the individual crystals are visible, the rock is called phaneritic; this is as the magma cools underground, while cooling may be fast or slow, cooling is slower than on the surface, so larger crystals grow. If it runs parallel to rock layers, it is called a sill. If an intrusion makes rocks above rise to form a dome, it is called a laccolith. How deep-seated intrusions burst through the overlying strata causes intrusive rock to be recognized: Veins spread out into branches, or branchlike parts result from filled cracks, the high temperature is evident in how they alter country rock; as heat dissipation is slow, as the rock is under pressure, crystals form, no vitreous chilled matter is present. The intrusions did not flow. Contained gases could not escape through the thick strata, thus form cavities, which can be observed; because their crystals are of the rough equal size, these rocks are said to be equigranular.
There is no distinction between a first generation of large well-shaped crystals and a fine-grained ground-mass. The minerals of each have formed in a definite order, each has had a period of crystallization that may be distinct or may have coincided with or overlapped the period of formation of some of the other ingredients. Earlier crystals originated at a time when most of the rock was still liquid and are more or less perfect. Crystals are less regular in shape because they were compelled to occupy the spaces left between the already-formed crystals; the former case is said to be idiomorphic. There are many other characteristics that serve to distinguish the members of these two groups. For example, orthoclase is feldspar from granite, while its modifications occur in lavas of similar composition; the same distinction holds for nepheline varieties. Leucite is common in lavas but rare in plutonic rocks. Muscovite is confined to intrusions; these differences show the influence of the physical conditions under which consolidation takes place.
Intrusive rocks formed at greater depths are called abyssal. Some intrusive rocks solidified in fissures as dikes and intrusive sills at shallow depth and are called subvolcanic or hypabyssal, they show structures intermediate between those of plutonic rocks. They are commonly porphyritic and sometimes vesicular. In fact, many of them are petrologically indistinguishable from lavas of similar composition. Ellicott City Granodiorite Guilford Quartz Monzonite Methods of pluton emplacement Norbeck Intrusive Suite Volcanic rock Woodstock Quartz Monzonite
A pegmatite is an igneous rock, formed underground, with interlocking crystals larger than 2.5 cm in size. Most pegmatites are found in sheets of rock near large masses of igneous rocks called batholiths; the word pegmatite derives from Homeric Greek, πήγνυμι, which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite. Most pegmatites are composed of quartz and mica, having a similar silicic composition as granite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions. Crystal size is the most striking feature of pegmatites, with crystals over 5 cm in size. Individual crystals over 10 metres long have been found, many of the world's largest crystals were found within pegmatites; these include spodumene, microcline and tourmaline. Crystal texture and form within pegmatitic rock may be taken to extreme size and perfection.
Feldspar within a pegmatite may display exaggerated and perfect twinning, exsolution lamellae, when affected by hydrous crystallization, macroscale graphic texture is known, with feldspar and quartz intergrown. Perthite feldspar within a pegmatite shows gigantic perthitic texture visible to the naked eye; the product of pegmatite decomposition is euclase. The single feature, diagnostic to all pegmatites is their large size crystal components. Pegmatite bodies are of minor size compared to typical intrusive rock bodies. Pegmatite body size is on the order of magnitude of one to a few hundred meters. Compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages. Crystal size and mineral assemblages are oriented parallel to the wall rock or concentric for pegmatite lenses; the number of crystal nuclei in pegmatites must be low and the ability of the necessary chemical components needed for crystal growth to migrate to the crystal surfaces must be enhanced to allow gigantic crystals to grow in pegmatites.
Thus, the possible growth mechanisms in a wide variety of known pegmatites may involve a combination of the following processes. The mineralogy of a pegmatite is in most cases dominated by some form of feldspar with mica and with quartz, being altogether "granitic" in character. Beyond that, pegmatite may include most minerals associated with granite and granite-associated hydrothermal systems, granite-associated mineralisation styles, for example greisens, somewhat with skarn associated mineralisation, it is however impossible to quantify the mineralogy of pegmatite in simple terms because of their varied mineralogy and difficulty in estimating the modal abundance of mineral species which are of only a trace amount. This is because of the difficulty in counting and sampling mineral grains in a rock which may have crystals from centimeters to meters across. Garnet almandine or spessartine, is a common mineral within pegmatites intruding mafic and carbonate-bearing sequences. Pegmatites associated with granitic domes within the Archaean Yilgarn Craton intruding ultramafic and mafic rocks contain red and brown almandine garnet.
Tantalum and niobium minerals are found in association with spodumene, tourmaline, cassiterite in the massive Greenbushes Pegmatite in the Yilgarn Craton of Western Australia, considered a typical metamorphic pegmatite unassociated with granite. Syenite pegmatites contain large feldspathoid crystals instead. Pegmatite is difficult to sample representatively due to the large size of the constituent mineral crystals. Bulk samples of some 50–60 kg of rock must be crushed to obtain a meaningful and repeatable result. Hence, pegmatite is characterised by sampling the individual minerals that compose the pegmatite, comparisons are made according to mineral chemistry. Geochemically, pegmatites have major element compositions approximating "granite", when found in association with granitic plutons it is that a pegmatite dike will have a different trace element composition with greater enrichment in large-ion lithophile elements, beryllium, aluminium and lithium, thorium, cesium, et cetera. Enrichment in the unusual trace elements will result in crystallisation of unusual and rare minerals such as beryl, columbite, zinnwaldite and so forth.
In most cases, there is no particular genetic significance to the presence of rare mineralogy within a pegmatite, however it is possible to see some causative and genetic links between, tourmaline-bearing granite dikes and tourmaline-bearing
Rwanda the Republic of Rwanda, is a country in Central and East Africa and one of the smallest countries on the African mainland. Located a few degrees south of the Equator, Rwanda is bordered by Uganda, Tanzania and the Democratic Republic of the Congo. Rwanda is in the African Great Lakes region and is elevated; the climate is temperate to subtropical, with two dry seasons each year. The population is predominantly rural, with a density among the highest in Africa. Rwandans are drawn from just one cultural and linguistic group, the Banyarwanda, although within this group there are three subgroups: the Hutu and Twa; the Twa are a forest-dwelling pygmy. Scholars disagree on differences between the Hutu and Tutsi. Christianity is the largest religion in the country; the sovereign state of Rwanda has a presidential system of government. The president is Paul Kagame of the Rwandan Patriotic Front, who took office in 2000. Rwanda today has low corruption compared with neighbouring countries, although human rights organisations report suppression of opposition groups and restrictions on freedom of speech.
The country has been governed by a strict administrative hierarchy since precolonial times. Rwanda is one of only two countries with a female majority in the national parliament. Hunter gatherers settled the territory in the stone and iron ages, followed by Bantu peoples; the population coalesced first into clans and into kingdoms. The Kingdom of Rwanda dominated from the mid-eighteenth century, with the Tutsi kings conquering others militarily, centralising power and enacting anti-Hutu policies. Germany colonised Rwanda in 1884 as part of German East Africa, followed by Belgium, which invaded in 1916 during World War I. Both European nations perpetuated a pro-Tutsi policy; the Hutu population revolted in 1959. They massacred numerous Tutsi and established an independent, Hutu-dominated state in 1962. A 1973 military coup saw a change of leadership; the Tutsi-led Rwandan Patriotic Front launched a civil war in 1990. The presidents of Rwanda and Burundi, both Hutus, died together when their aeroplane was shot down in April 1994.
Social tensions erupted in the 1994 genocide, in which Hutu extremists killed an estimated 500,000 to 1 million Tutsi and moderate Hutu. The RPF ended the genocide with a military victory. Rwanda's economy suffered in wake of the 1994 genocide, but has since strengthened; the economy is based on subsistence agriculture. Coffee and tea are the major cash crops for export. Tourism is a fast-growing sector. Rwanda is one of only two countries in which mountain gorillas can be visited safely, visitors pay high prices for gorilla tracking permits. Music and dance are an integral part of Rwandan culture drums and the choreographed intore dance. Traditional arts and crafts are produced throughout the country, including imigongo, a unique cow dung art; the name "Rwanda" is derived from the Rwanda-Rundi word rwanda meaning "domain" or an "area occupied by a swarm". The official name of the country was "Rwandese Republic" until May 2003, when the adoption of a new national constitution changed it to its current name of "Republic of Rwanda".
Modern human settlement of what is now Rwanda dates from, at the latest, the last glacial period, either in the Neolithic period around 8000 BC, or in the long humid period which followed, up to around 3000 BC. Archaeological excavations have revealed evidence of sparse settlement by hunter gatherers in the late stone age, followed by a larger population of early Iron Age settlers, who produced dimpled pottery and iron tools; these early inhabitants were the ancestors of the Twa, aboriginal pygmy hunter-gatherers who remain in Rwanda today. Between 700 BC and 1500 AD, a number of Bantu groups migrated into Rwanda, clearing forest land for agriculture; the forest-dwelling Twa moved to the mountain slopes. Historians have several theories regarding the nature of the Bantu migrations. An alternative theory is that the migration was slow and steady, with incoming groups integrating into rather than conquering the existing society. Under this theory, the Hutu and Tutsi distinction arose and was a class distinction rather than a racial one.
The earliest form of social organisation in the area was the clan. The clans were not limited to genealogical lineages or geographical area, most included Hutu and Twa. From the 15th century, the clans began to coalesce into kingdoms. One of these, the Kingdom of Rwanda, ruled by the Tutsi Nyiginya clan, became dominant from the mid-eighteenth century; the kingdom reached its greatest extent during the nineteenth century under the reign of King K
Sphalerite is a mineral, the chief ore of zinc. It consists of zinc sulfide in crystalline form but always contains variable iron; when iron content is high it is an opaque black variety, marmatite. It is found in association with galena and other sulfides along with calcite and fluorite. Miners have been known to refer to sphalerite as zinc blende, black-jack and ruby jack; the mineral crystallizes in the cubic crystal system. Like other minerals with a cubic crystal structure, sphalerite may show a tetrahedral crystal habit. In the crystal structure and sulfur atoms are tetrahedrally coordinated; the structure is related to the structure of diamond. The hexagonal analog is known as the wurtzite structure; the lattice constant for zinc sulfide in the zinc blende crystal structure is 0.541 nm, calculated from geometry and ionic radii of 0.074 nm and 0.184 nm. It forms ABCABC layers. All natural sphalerites contain finite concentrations of various impurity elements; these substitute for the zinc position in the lattice.
The most common are Cd and Mn, but Ga, Ge and In may be present in high concentrations. The abundances of these elements are controlled by the conditions under which the sphalerite formed, most formation temperature and fluid composition, its color is yellow, brown, or gray to gray-black, it may be shiny or dull. Its luster is resinous to submetallic for high iron varieties, it has a yellow or light brown streak, a Mohs hardness of 3.5–4, a specific gravity of 3.9–4.1. Some specimens have a red iridescence within the gray-black crystals; the pale yellow and red varieties have little iron and are translucent. The darker, more opaque varieties contain more iron; some specimens are fluorescent in ultraviolet light. The refractive index of sphalerite is 2.37. Sphalerite possesses perfect dodecahedral cleavage. Gemmy, pale specimens from Franklin, New Jersey, are fluorescent orange and/or blue under longwave ultraviolet light and are known as cleiophane, an pure ZnS variety. Sphalerite is found in thousands of locations worldwide.
Sources of high quality crystals include: Sphalerite is the most important ore of zinc. Around 95% of all primary zinc is extracted from sphaleritic ores. However, due to its variable trace element content, sphalerite is an important source of several other elements, such as cadmium, gallium germanium, indium. Crystals of suitable size and transparency have been fashioned into gemstones featuring the brilliant cut to best display sphalerite's high dispersion of 0.156, over three times that of diamond. Freshly cut gems have an adamantine luster. Owing to their softness and fragility the gems are left unset as collector's or museum pieces. Gem-quality material is a yellowish to honey brown, red to orange, or green. List of minerals Dana's Manual of Mineralogy ISBN 0-471-03288-3 Webster, R. Read, P. G.. Gems: Their sources and identification, p. 386. Butterworth-Heinemann, Great Britain. ISBN 0-7506-1674-1 Minerals.net Minerals of Franklin, NJ The sphalerite structure Possible relation of Sphalerite to origins of life and precursor chemicals in'Primordial Soup'
Granite is a common type of felsic intrusive igneous rock, granular and phaneritic in texture. Granites can be predominantly white, pink, or gray depending on their mineralogy; the word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. Speaking, granite is an igneous rock with between 20% and 60% quartz by volume, at least 35% of the total feldspar consisting of alkali feldspar, although the term "granite" is used to refer to a wider range of coarse-grained igneous rocks containing quartz and feldspar; the term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin. These rocks consist of feldspar, quartz and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole peppering the lighter color minerals; some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic.
A granitic rock with a porphyritic texture is known as a granite porphyry. Granitoid is a descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids; the extrusive igneous rock equivalent of granite is rhyolite. Granite is nearly always massive and tough; these properties have made granite a widespread construction stone throughout human history. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength lies above 200 MPa, its viscosity near STP is 3–6·1019 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C. Granite has poor primary permeability overall, but strong secondary permeability through cracks and fractures if they are present. Granite is classified according to the QAPF diagram for coarse grained plutonic rocks and is named according to the percentage of quartz, alkali feldspar and plagioclase feldspar on the A-Q-P half of the diagram.
True granite contains both alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite; when a granitoid contains less than 10% orthoclase, it is called tonalite. A granite containing both muscovite and biotite micas is called two-mica granite. Two-mica granites are high in potassium and low in plagioclase, are S-type granites or A-type granites. A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses: Granite containing rock is distributed throughout the continental crust. Much of it was intruded during the Precambrian age. Outcrops of granite tend to form rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite occurs as small, less than 100 km2 stock masses and in batholiths that are associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are associated with the margins of granitic intrusions.
In some locations coarse-grained pegmatite masses occur with granite. Granite is more common in continental crust than in oceanic crust, they are crystallized from felsic melts which are less dense than mafic rocks and thus tend to ascend toward the surface. In contrast, mafic rocks, either basalts or gabbros, once metamorphosed at eclogite facies, tend to sink into the mantle beneath the Moho. Granitoids have crystallized from felsic magmas that have compositions near a eutectic point. Magmas are composed of minerals in variable abundances. Traditionally, magmatic minerals are crystallized from the melts that have separated from their parental rocks and thus are evolved because of igneous differentiation. If a granite has a cooling process, it has the potential to form larger crystals. There are peritectic and residual minerals in granitic magmas. Peritectic minerals are generated through peritectic reactions, whereas residual minerals are inherited from parental rocks. In either case, magmas will evolve to the eutectic for crystallization upon cooling.
Anatectic melts are produced by peritectic reactions, but they are much less evolved than magmatic melts because they have not separated from their parental rocks. The composition of anatectic melts may change toward the magmatic melts through high-degree fractional crystallization. Fractional crystallisation serves to reduce a melt in iron, titanium and sodium, enrich the melt in potassium and silicon – alkali feldspar and quartz, are two of the defining constituents of granite; this process operates regardless of the origin of parental magmas to granites, regardless of their chemistry. The composition and origin of any magma that differentiates into granite leave certain petrological evidence as to what the granite's parental rock was; the final texture and composition of a granite are distinctive as to its parental rock. For instance, a granite, derived from partial melting of meta
Galena called lead glance, is the natural mineral form of lead sulfide. It is an important source of silver. Galena is one of the most abundant and distributed sulfide minerals, it crystallizes in the cubic crystal system showing octahedral forms. It is associated with the minerals sphalerite and fluorite. Galena is the main ore of lead, used since ancient times; because of its somewhat low melting point, it was easy to liberate by smelting. It forms in low-temperature sedimentary deposits. In some deposits the galena contains about 1–2% silver, a byproduct that far outweighs the main lead ore in revenue. In these deposits significant amounts of silver occur as included silver sulfide mineral phases or as limited silver in solid solution within the galena structure; these argentiferous galenas have long been an important ore of silver. Galena deposits are found worldwide in various environments. Noted deposits include those at Freiberg in Saxony. In the United States, it occurs most notably in the Mississippi Valley type deposits of the Lead Belt in southeastern Missouri, in the Driftless Area of Illinois and Wisconsin.
Galena was a major mineral of the zinc-lead mines of the tri-state district around Joplin in southwestern Missouri and the adjoining areas of Kansas and Oklahoma. Galena is an important ore mineral in the silver mining regions of Colorado, Idaho and Montana. Of the latter, the Coeur d'Alene district of northern Idaho was most prominent. Galena is the official state mineral of the U. S. states of Wisconsin. The largest documented crystal of galena is composite cubo-octahedra from the Great Laxey Mine, Isle of Man, measuring 25 cm × 25 cm × 25 cm. Galena belongs to the octahedral sulfide group of minerals that have metal ions in octahedral positions, such as the iron sulfide pyrrhotite and the nickel arsenide niccolite; the galena group is named after its most common member, with other isometric members that include manganese bearing alabandite and niningerite. Divalent lead cations and sulfur anions form a close-packed cubic unit cell much like the mineral halite of the halide mineral group. Zinc, iron, antimony, arsenic and selenium occur in variable amounts in galena.
Selenium substitutes for sulfur in the structure constituting a solid solution series. The lead telluride mineral altaite has the same crystal structure as galena. Within the weathering or oxidation zone galena alters to cerussite. Galena exposed to acid mine drainage can be oxidized to anglesite by occurring bacteria and archaea, in a process similar to bioleaching. One of the oldest uses of galena was in the eye cosmetic kohl. In Ancient Egypt, this was applied around the eyes to reduce the glare of the desert sun and to repel flies, which were a potential source of disease. Galena is the primary ore of lead, used in making lead–acid batteries. Galena is mined for its silver content, such as at the Galena Mine in northern Idaho. Known as "potter's ore", galena is used in a green glaze applied to pottery. Galena is a semiconductor with a small band gap of about 0.4 eV, which found use in early wireless communication systems. It was used as the crystal in crystal radio receivers, in which it was used as a point-contact diode capable of rectifying alternating current to detect the radio signals.
The galena crystal was used with a sharp wire, known as a "cat's whisker" in contact with it. The operation of the radio required that the point of contact on the galena be shifted about to find a part of the crystal that acted as a rectifying diode. Making such wireless receivers was a popular home hobby in Britain and other European countries during the 1930s. Scientists associated with the investigation of the diode effect are Karl Ferdinand Braun and Jagadish Bose. In modern wireless communication systems, galena detectors have been replaced by more reliable semiconductor devices. List of minerals Lead smelter Klein, Cornelis. Manual of Mineralogy. Wiley. Pp. 274–276. ISBN 0-471-80580-7. Case Studies in Environmental Medicine: Lead Toxicity. ToxFAQs: Lead. Mineral Information Institute entry for lead