Within Nigeria Mysteries
When Strange Objects Fell From Nigeria's Sky
Meteorite falls such as Gujba show how frightening sky events can become scientifically verified mysteries.
On this page
- Documented meteorite falls and discoveries
- How scientists identify space rocks
- Why strange lights create mysteries
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Introduction
Nigeria’s most convincing sky mysteries are not tales of imaginary objects, but real pieces of space that arrived with dramatic eyewitness reports and later became scientific specimens. The best-known example is the Gujba meteorite, which fell in Yobe State in 1984 after witnesses saw a bright fireball and heard an explosion. What first looked like a frightening event from the heavens became an internationally studied meteorite with a rare composition.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Entry for GujbaLPIMeteoritical Bulletin: Entry for Gujba
Other Nigerian meteorites, including Geidam, Gashua, Udei Station, and Uwet, show a recurring pattern: a strange sight or unexplained object may begin as a local mystery, but physical evidence can transform it into a measurable scientific event. Nigeria’s meteorite record is therefore a useful example of how unusual sky reports move from rumour and eyewitness memory into geology, chemistry and planetary science.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Search the DatabaseLPIMeteoritical Bulletin: Search the Database
Documented meteorite falls and discoveries
Nigeria’s official meteorite record contains both witnessed falls — where people saw the object arrive — and finds discovered later without a recorded fall. This distinction matters because a witnessed fall provides a rare connection between the dramatic event in the sky and the object recovered on the ground.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Search the DatabaseLPIMeteoritical Bulletin: Search the Database
Gujba: the strange fireball that became a scientific landmark
The Gujba meteorite is Nigeria’s most famous sky fall. On 3 April 1984, near Bogga Dingare in present-day Yobe State, a bright fireball was seen travelling across the sky before an explosion was heard. A meteorite mass fell into a corn field, creating the kind of event that could easily have been interpreted as supernatural or mysterious by observers who had no way to identify it.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Entry for GujbaLPIMeteoritical Bulletin: Entry for Gujba
The recovered material proved extraordinary. Gujba was classified as a rare CBa carbonaceous meteorite (a type of primitive space rock with unusual proportions of metal and silicate material). The official record gives the original mass as about 100 kilograms and identifies it as an observed fall.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Entry for GujbaLPIMeteoritical Bulletin: Entry for Gujba
Its scientific importance comes from what the rock revealed. Studies found that Gujba contains unusual metal and silicate globules, structures that provide clues about processes in the early Solar System. Researchers have described it as the first observed fall among the Bencubbin-like meteorites, making a Nigerian village the location of a globally significant planetary science sample.[ScienceDirect]sciencedirect.comFormation of metal and silicate globules in Gujba: a new Bencubbin-like meteorite fall - ScienceDirect…
The human side of the story is also part of its mystery. Much of the original material was broken apart and dispersed after the fall, with fragments passing through many hands. This is common with unusual objects found after dramatic events: before scientific classification, people naturally treat them as curiosities, souvenirs or objects of local interest.[Mindat]mindat.orgloc 253779Gujba meteorite, Bogga Dingare, Yobe, NigeriaAug 17, 2025 — In the early evening of April 3, 1984 the meteorite fell in a corn fiel…
Other Nigerian meteorites: a wider pattern
Gujba is not an isolated case. The Meteoritical Bulletin Database records several officially recognised Nigerian meteorites. These include:
- Geidam — an observed 1950 fall in Yobe State, classified as an H5 ordinary chondrite with a recorded mass of about 725 grams.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Search the DatabaseLPIMeteoritical Bulletin: Search the Database
- Gashua — an observed 1984 fall in Yobe State, classified as an L6 ordinary chondrite with a recorded mass of 4.16 kilograms.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Search the DatabaseLPIMeteoritical Bulletin: Search the Database
- Udei Station — a much larger iron meteorite found in Nigeria, recorded as an observed fall from 1927 with a mass of about 103 kilograms.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Entry for Udei StationLPIMeteoritical Bulletin: Entry for Udei Station
- Uwet — an iron meteorite found in 1903, weighing about 54 kilograms, although it was not an observed fall.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Entry for UwetLPIMeteoritical Bulletin: Entry for Uwet
Together, these examples show that Nigeria’s “objects from the sky” are not only folklore or uncertain sightings. Some are physical samples that can be examined, classified and compared with meteorites from around the world.
How scientists identify space rocks
A falling object is only the beginning of the investigation. A dark stone found after a bright flash may be a meteorite, but it may also be an ordinary Earth rock, industrial material or mineral deposit. Scientists rely on several lines of evidence before confirming an object’s extraterrestrial origin.[meteorites.asu.edu]meteorites.asu.eduHow can I find a meteorite? – Buseck Center for Meteorite StudiesHow can I find a meteorite? – Buseck Center for Meteorite Studies
One important clue is a fusion crust — a thin, dark outer layer formed when the surface of a meteoroid melts during its high-speed passage through Earth’s atmosphere and then cools before landing. Fresh meteorites often preserve this glassy-looking coating.[LPI]lpi.usra.eduLPI10. Meteorite with Fusion CrustLPI10. Meteorite with Fusion Crust
Researchers also examine:
- Mineral structure: Meteorites contain mineral combinations and textures that differ from many common Earth rocks.[Natural History Museum]nhm.ac.ukNatural History Museum Types of meteorites | Natural History MuseumNatural History Museum Types of meteorites | Natural History Museum
- Chemical composition: Laboratory analysis can reveal elemental patterns associated with known meteorite groups.[Natural History Museum]nhm.ac.ukNatural History Museum Types of meteorites | Natural History MuseumNatural History Museum Types of meteorites | Natural History Museum
- Magnetic properties and metal content: Many meteorites contain iron-nickel metal, though magnetism alone is not enough for identification.[meteorites.asu.edu]meteorites.asu.eduHow can I find a meteorite? – Buseck Center for Meteorite StudiesHow can I find a meteorite? – Buseck Center for Meteorite Studies
- Location and fall history: A witnessed fall, a recorded fireball and a collection site can strengthen the case by linking the object to a specific event.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Entry for GujbaLPIMeteoritical Bulletin: Entry for Gujba
This process explains why meteorites are valuable evidence in the study of sky mysteries. The key difference between a strange object and a scientific discovery is not how unusual it appears, but whether it can be tested.
Why strange lights create mysteries
Meteorite falls are the clearest examples of sky mysteries becoming science, but bright objects in the sky often remain unexplained at first. A flash, streak or explosion-like sound can have many possible causes, including meteors, aircraft, satellites, atmospheric effects or other human-made objects.
Nigeria’s large land area, varied landscapes and many rural communities create conditions where unusual observations can become memorable stories. A person watching the night sky may genuinely report something strange without having enough information to identify it immediately. The word “unidentified” describes a lack of explanation, not proof of an extraordinary cause.
Meteor events are particularly confusing because the visible phenomenon and the physical object are separated. A bright streak may last only seconds, while fragments — if any survive the fall — may land many kilometres away. Even a genuine meteorite fall can therefore begin with uncertainty before evidence is recovered.
The Gujba event illustrates this transition perfectly. Witnesses first experienced a dramatic fireball and explosion. Scientists later studied a rare meteorite whose composition offered information about the formation of materials in the early Solar System. The mystery was not destroyed by science; it was transformed into a deeper and more accurate story.[LPI]lpi.usra.eduLPIMeteoritical Bulletin: Entry for GujbaLPIMeteoritical Bulletin: Entry for Gujba
What Nigeria’s meteorites reveal about evidence and mystery
Nigerian meteorite cases occupy an unusual place between folklore and science. They begin with the oldest human reaction to unexpected events — wonder and uncertainty — but they can end with carefully measured evidence.
The strongest cases share three features:
- A witnessed event: people saw something unusual happen in the sky.
- A recovered object: physical material was collected rather than relying only on memory.
- Scientific confirmation: laboratories classified the material and compared it with known meteorite groups.
This makes Nigerian meteorites different from many other sky mysteries. A strange light may remain only a story, but a meteorite can become a permanent record of an event that crossed the boundary between Earth and space. Nigeria’s documented falls show how an apparently impossible event — a rock arriving from the heavens — can move from fear and speculation into one of the most evidence-based forms of mystery.
Amazon book picks
Further Reading
Books and field guides related to When Strange Objects Fell From Nigeria's Sky. Use these as the next step if you want deeper reading beyond the article.
The Cambridge Encyclopedia of Meteorites
Covers meteorite types, identification, falls, and scientific investigation in depth.
The vanishing hitchhiker
First published 1981. Subjects: History and criticism, Legends, Urban folklore, Légendes, Folklore urbain.
Endnotes
1.
Source: lpi.usra.edu
Title: LPIMeteoritical Bulletin: Entry for Gujba
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?ants=&browse=&categ=Carbonaceous+chondrites+%28type%29&code=11449&country=All&falls=&lrec=2000&map=ge&mblist=All&nwas=&phot=no&pnt=Normal+table&rect=&sea=&sfor=names&snew=0&srt=type&strewn=no&stype=contains&valids=
2.
Source: sciencedirect.com
Link:https://www.sciencedirect.com/science/article/abs/pii/S001670370300098X
Source snippet
Formation of metal and silicate globules in Gujba: a new Bencubbin-like meteorite fall - ScienceDirect...
3.
Source: lpi.usra.edu
Title: LPIMeteoritical Bulletin: Search the Database
Link:https://www.lpi.usra.edu/meteor/metbull.php?ants=&browse=&categ=All&country=Nigeria&dr=&falls=&lrec=1000&map=ge&mblist=All&nwas=&page=0&phot=&pnt=Normal+table&rect=&sea=Yobe&sfor=places&snew=0&srt=mass&strewn=&stype=exact&valids=
4.
Source: lpi.usra.edu
Title: LPIMeteoritical Bulletin: Entry for Udei Station
Link:https://www.lpi.usra.edu/meteor/metbull.php?code=24101
5.
Source: lpi.usra.edu
Title: LPIMeteoritical Bulletin: Entry for Uwet
Link:https://www.lpi.usra.edu/meteor/metbull.php?code=24138
6.
Source: mindat.org
Title: loc 253779
Link:https://www.mindat.org/loc-253779.html
Source snippet
Gujba meteorite, Bogga Dingare, Yobe, NigeriaAug 17, 2025 — In the early evening of April 3, 1984 the meteorite fell in a corn fiel...
Published: April 3, 1984
7.
Source: lpi.usra.edu
Title: LPIMeteoritical Bulletin: Entry for Gashua
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?ants=&browse=&categ=Enstatite+chondrites+%28type-7%29&code=44882&country=All&falls=&lrec=5000&map=ge&mblist=All&nwas=&phot=no&pnt=Normal+table&rect=&sea=&sfor=names&snew=0&srt=mass&strewn=no&stype=contains&valids=
Source snippet
Abbreviation: There is no official abbreviation for this meteorite. Observed fall: Yes Year fell: 1984...
8.
Source: meteorites.asu.edu
Title: How can I find a meteorite? – Buseck Center for Meteorite Studies
Link:https://meteorites.asu.edu/meteorites/how-can-i-find-a-meteorite
9.
Source: askanexpert.asu.edu
Title: Identifying meteorites | Ask An Expert
Link:https://askanexpert.asu.edu/earthspace/identifying-meteorites
Source snippet
SHOW/HIDE WORDS TO KNOW FRICTIONAL HEAT the heat made by rubbing two things together. MINERAL solid, inorganic (do not come from plants o...
10.
Source: lpi.usra.edu
Title: LPIMeteorites and Their Properties
Link:https://www.lpi.usra.edu/science/kring/epo_web/meteorites/appearance.html
Source snippet
THE APPEARANCE OF A FRESHLY-FALLEN METEORITE The most important primitive meteorites are generally those that were observed falling and c...
11.
Source: mindat.org
Title: Udei Station meteorite, Benue River, Niger, Nigeria
Link:https://www.mindat.org/loc-123037.html
Source snippet
March 30, 2026 — UDEI STATION METEORITE, BENUE RIVER, NIGER, NIGERIAI Regional Level Types --- Udei Station meteorite | Meteorite Fall Lo...
Published: March 30, 2026
12.
Source: meteorites.asu.edu
Title: According to the Meteo
Link:https://meteorites.asu.edu/meteorites/gujba
Source snippet
Buseck Center for Meteorite StudiesApril 1, 2025 — GUJBA Image By Center for Meteorite Studies April 1, 2025 * Meteorites April’s Meteo...
Published: April 1, 2025
13.
Source: sciencedirect.com
Link:https://www.sciencedirect.com/science/article/pii/S0016703721006736
Source snippet
SAMPLES A range of compositional and metamorphic types of carbonaceous, ordinary and enstatite chondrites were analyzed to understand, mo...
14.
Source: meteorites.asu.edu
Title: specimen catalogue
Link:https://meteorites.asu.edu/collection/specimen-catalogue
Source snippet
Moore Meteorite Collection (PDF, last updated September, 2024), or use the searchable table below. Request a specimen loan M...
15.
Source: meteorites.com
Title: 2020 haag meteorite catalog page 9
Link:https://meteorites.com/2020-haag-meteorite-catalog-page-9/
Source snippet
2020 HAAG METEORITE CATALOG PAGE 9 PG 1 | PG 2 | PG 3 | PG 4 | PG 5 | PG 6 | PG 7 | PG 8 | PG 9 | PG 10 | PG 11 Sikhote Alin, R...
16.
Source: meteoritical.org
Link:https://meteoritical.org/publications/meteoritical-bulletin
17.
Source: lpi.usra.edu
Title: LPI10. Meteorite with Fusion Crust
Link:https://www.lpi.usra.edu/publications/slidesets/marslife/slide_10.html
18.
Source: nhm.ac.uk
Title: Natural History Museum Types of meteorites | Natural History Museum
Link:https://www.nhm.ac.uk/discover/types-of-meteorites.html
19.
Source: skyfallmeteorites.com
Title: At 6:30 in the evening, a bri
Link:https://skyfallmeteorites.com/education-research/david-weir-meteorite-studies/chondrite/carbonaceous-cb/gujba
Source snippet
Gujba - SkyFall MeteoritesNovember 8, 2018 — GUJBA Posted on November 8, 2018November 1, 2019 by skyfallmeteorites CBa, bencubbinite Imag...
Published: November 8, 2018
20.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?ants=&browse=&categ=CV-CK+clan+chondrites&code=67799&country=All&falls=&lrec=5000&map=ge&mblist=All&nwas=&phot=no&pnt=Normal+table&rect=&sea=&sfor=names&snew=0&srt=name&strewn=no&stype=contains&valids=
Source snippet
Abbreviation: There is no official abbreviation for this meteorite. Observed fall: Yes, confirmed f...
21.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?ants=&browse=&categ=All&code=44882&country=All&falls=&lrec=1000&map=ge&mblist=All&nwas=&phot=no&pnt=Normal+table&rect=&sea=L6&sfor=types&snew=0&srt=mass&strewn=no&stype=exact&valids=
Source snippet
Abbreviation: There is no official abbreviation for this meteorite. Observed fall: Yes Year fell: 1984...
22.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?country=Nigeria&lrec=200&sea=Yobe&sfor=places&srt=year&stype=exact
Source snippet
Bulletin: Search the DatabaseMeteoritical Bulletin Database Search the Database Name | Status | Fall | Year | Place | Type | Mass | MetBu...
23.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?country=Nigeria&lrec=50&sea=&sfor=names&srt=name&stype=contains
Source snippet
Bulletin: Search the DatabaseMeteoritical Bulletin Database Search the Database Search for: [Input] Names [Input] Text [Input] Places [In...
24.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/?country=Nigeria&lrec=50&sea=&sfor=names&srt=name&stype=contains
Source snippet
Bulletin: Search the DatabaseMeteoritical Bulletin Database Search the Database Name | Abbrev | Status | Fall | Year | Place | Type | Mas...
25.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?country=Nigeria&lrec=50&sea=&sfor=names&srt=type&stype=contains
Source snippet
Bulletin: Search the DatabaseMeteoritical Bulletin Database Search the Database Search for: [Input] Names [Input] Text [Input] Places [In...
26.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.php?code=11449
Source snippet
Bulletin: Entry for GujbaGujba. Yobe, Nigeria. Fell 1984 April 3, 18:30 local time. Bencubbin-like meteorite. A conical meteorite fell in...
27.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?lrec=200&sea=CBa&sfor=types&srt=name&stype=exact
Source snippet
Bulletin: Search the DatabaseGujba **, Official, Y, 1984, Yobe, Nigeria, CBa, 100 kg, 85 · Google Earth · Northwest Africa 1814 **, NWA 1...
28.
Source: lpi.usra.edu
Title: Gujba texturally resembles Ben-.Read more
Link:https://www.lpi.usra.edu/meetings/lpsc2001/pdf/1779.pdf
Source snippet
usra.edugujba: a new bencubbin-like meteorite fall from nigeria.by AE Rubin · Cited by 12 — The Gujba, Nigeria meteorite is the first ob...
29.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?country=Nigeria&lrec=2000&sea=&sfor=names&srt=mass&stype=contains
Source snippet
Bulletin: Search the DatabaseAba Panu · 2018 · Oyo, Nigeria · L3 · 160 kg; Udei Station · 1927 · Benue, Nigeria · Iron, IAB-ung · 103 kg...
30.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/science/kring/epo_web/meteorites/composition.html
Source snippet
and Their Properties - The Structure and Composition of MeteoritesImage: Meteorites and Their Properties * * * THE STRUCTURE AND COMPOSIT...
31.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.cfm?ants=&browse=&categ=IIAB+irons&code=24138&country=All&falls=&lrec=2000&map=ge&mblist=All&nwas=&phot=no&pnt=Normal+table&rect=&sea=&sfor=names&snew=0&srt=type&strewn=no&stype=contains&valids=
Source snippet
Abbreviation: There is no official abbreviation for this meteorite. Observed fall: No Year found: 1903 Coun...
32.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.php?country=Nigeria&lrec=50&sea=&sfor=names&srt=mass&stype=contains
Source snippet
Bulletin: Search the DatabaseMeteoritical Bulletin Database Search the Database Search for: [Input] Names [Input] Text [Input] Places [In...
33.
Source: meteoritelab.com
Title: It was recovered for a shallow hole 8 years after it fell. ZAGAM
Link:https://meteoritelab.com/location/nigeria/
Source snippet
Nigeria | Southwest Meteorite Laboratory* # Location: Nigeria UDEI STATION Udei Station meteorite fall is said to have sounded like a fre...
34.
Source: monnigmuseum.tcu.edu
Link:https://monnigmuseum.tcu.edu/meteorites/gujba/
Source snippet
Location: Yobe, Nigeria. At 1830 hours the night of April 3, 1984, the Gujba meteorite fell above Yobe, Nigeria and had a total weight of...
Published: April 3, 1984
35.
Source: lpi.usra.edu
Link:https://www.lpi.usra.edu/meteor/metbull.php?code=10870
Source snippet
Abbreviation: There is no official abbreviation for this meteorite. Observed fall: Yes Year fell: 1950...
Additional References
36.
Source: nasa.gov
Link:https://www.nasa.gov/solar-system/u-s-space-force-releases-decades-of-bolide-data-to-nasa-for-planetary-defense-studies/
Source snippet
Space Force Releases Decades of Bolide Data to NASA for Planetary Defense Studies - NASAApril 7, 2022 — 5 min read U.S. SPACE FORCE RELEA...
Published: April 7, 2022
37.
Source: nasa.gov
Title: Tiny Asteroid Discovered Saturday Disintegrates Hours Later Over Southern Africa
Link:https://www.nasa.gov/solar-system/asteroids/tiny-asteroid-discovered-saturday-disintegrates-hours-later-over-southern-africa/
Source snippet
June 3, 2018 — 5 min read TINY ASTEROID DISCOVERED SATURDAY DISINTEGRATES HOURS LATER OVER SOUTHERN AFRICA Image: The headshot image...
Published: June 3, 2018
38.
Source: cambridge.org
Link:https://www.cambridge.org/core/journals/mineralogical-magazine-and-journal-of-the-mineralogical-society/article/abs/meteorites-of-uwet-kota-kota-and-angela-redeterminations-of-nickel-and-iron-in-the-baroti-and-wittekrantz-meteoric-stones1/59D451E94A8DE6E41C867C10FD3C17ED
Source snippet
eralogical magazine and journal of the Mineralogical Society | Cambridge CoreMarch 14, 2018 — THE METEORITES OF UWET, KOTA KOTA, AND ANGE...
Published: March 14, 2018
39.
Source: meteoritelab.com
Link:https://meteoritelab.com/product/udei-station-uds89/
Source snippet
Image SILICATED-IRON MOSAIC The meteorite location is a witnessed fall in 1924 Nigeria. The etched slice, a mosaic, with a variety of sil...
40.
Source: researchgate.net
Link:https://www.researchgate.net/publication/351100234_Studies_of_Near_earth_Objects_Meteorites_which_Landed_in_Nigeria
41.
Source: ebay.com
Link:https://www.ebay.com/itm/397642213130?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339151051&customid=endnote-source&toolid=10001
Source snippet
This slice is polished on one side and evenly cut. Bencubbinite, CBa. 10.593 gram slice. Fell April 3, 1984 ~18:30...
Published: April 3, 1984
42.
Source: meteorite-museum.org
Link:https://www.meteorite-museum.org/cb
Source snippet
EPMA (L. Garvie, ASU): Low Ca pyroxene Fs3.17±0.79Wo1.88±2.62 (n=4), Al2O3 = 0.4 to 3.2, TiO2 = 0.1 to...
43.
Source: jpl.nasa.gov
Title: Credit: NASA/JPL-Caltech These are the discover
Link:https://www.jpl.nasa.gov/news/tiny-asteroid-discovered-saturday-disintegrates-hours-later-over-southern-africa/
Source snippet
Asteroid Discovered Saturday Disintegrates Hours Later Over Southern Africa | NASA Jet Propulsion Laboratory (JPL)June 3, 2018 —.4 min r...
Published: June 3, 2018
44.
Source: nasa.gov
Title: NAS A System Predicts Impact of Small Asteroid
Link:https://www.nasa.gov/solar-system/nasa-system-predicts-impact-of-small-asteroid/
Source snippet
NASA System Predicts Impact of Small Asteroid - NASAMarch 15, 2022 — 5 min read NASA SYSTEM PREDICTS IMPACT OF SMALL ASTEROID Jet Propuls...
Published: March 15, 2022
45.
Source: researchgate.net
Title: (PDF) Gujba: A new Bencubbin-like meteorite fall from Nigeria
Link:https://www.researchgate.net/publication/42793836_Gujba_A_new_Bencubbin-like_meteorite_fall_from_Nigeria
Source snippet
March 1, 2001 — Article PDF Available GUJBA: A NEW BENCUBBIN-LIKE METEORITE FALL FROM NIGERIA * March 2001 Authors: ABSTRACT Gujba is a n...
Published: March 1, 2001
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