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Fulgurite: a Unique Mineral Formed by Impact of Lightening

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Fulgurite: a Unique Mineral Formed by Impact of Lightening Open Access e-Journal Earth Science India - www.earthscienceindia.info Popular Issue, V (IV), October, 2012, p. 1-8 Fulgurite: A unique mineral formed by impact of lightening Arun Kumar This study discloses new facts about the environment of the ancient Sahara Desert and the chemical changes during the interaction between atmosphere and lightning. It also shows that fulgurites are archives of ancient lightning, atmospheres and ecology. In June, 2012, I visited the Museum of Science in Boston, U.S.A. and saw a couple of presentations (Figures 1 and 2) about petrified lightning. In my over forty years as a petroleum geologist, stratigraphic palynologist and environmental micropaleontologist, I had never heard of fulgurite and could not imagine that a term ‘petrified lightning’ exists. However, I certainly believe that mineralogists and other well-informed geologists are more likely to be aware of this phenomenon as well as this mineral. I felt intrigued and decided to learn more about it. The display (Figure 1) at the museum reads as follows: Petrified Lightning: This rare mineral formation called the fulgurite, was produced in less than one ten- thousands of a second when lightning struck the ground near Columbia, South Carolina. The lightning bolt traveled through a thick layer of dry sand and it heated to a temperature greater than 1800 0 C (3200 0 F). The sand was instantly melted and blown aside, forming a thin, glassy tube surrounding the path of the lightning bolt. Fulgurites as long as this are rare; most are less than 30 cm (one foot) long. Lent by Mineralogical Museum Harvard University Navarro-González et al. (2007) describe fulgurites as “When lightning strikes the ground, it heats, melts, and fuses the sand in the soils to for form glass tubes known as fulgurites .” Carter et al. (2010) further elaborate and define this term as “A fulgurite is an amorphous mineraloid, a superheated glassy solid that is formed when a lightning bolt hits a sandy or rocky ground and thermal energy is transferred.” Carl Ege of the Utah Geological Survey explains that (website 1), “Fulgurites are natural tubes or crusts of glass formed by the fusion of silica (quartz) sand or rock from a lightning strike. Their shape mimics the path of the lightning bolt as it disperses into the ground ”. He further explains that, “ All lightning strikes that hit the ground are capable of forming fulgurites. A temperature of 1800 degrees Celsius is required to instantaneously melt sand and form a fulgurite (most lightning strikes have a temperature of 2500 degrees Celsius). Fulgurites have been found worldwide, but are relatively rare. Two types of 1 Open Access e-Journal Earth Science India - www.earthscienceindia.info Popular Issue, V (IV), October, 2012, p. 1-8 fulgurites have been recognized: sand (Figures 5 and 6) and rock fulgurites (Figure 4). Sand fulgurites are the most common and are generally found in beach or desert regions containing clean (free of fine-grained silt or clay), dry sand. They resemble roots or branching tube-like structures that have a rough surface, covered with partially melted sand grains. Sand fulgurite tubes have a glassy interior, due to rapid cooling and solidification of the sand after the lightning strike. The size and length of a fulgurite depends on the strength of the lightning strike and the thickness of the sand bed. Many sand fulgurites average 1 or 2 inches in diameter and can be up to 30 inches long .” Figure 1: A display describing petrified lightning and fulgurite at the Boston Museum of Science, Boston. (Photo: the author, June, 2012) Figure 2: A display of fulgurite at the Boston Museum of Science, Boston. (Photo: the author, June, 2012) 2 Open Access e-Journal Earth Science India - www.earthscienceindia.info Popular Issue, V (IV), October, 2012, p. 1-8 Wikipedia (website 2) explains the term fulgurite as ‘petrified lightning’ and refers to the glass formed as ‘lechatelierite’ which is classified as a mineraloid because it is amorphous. Fulgurites may occur as deep as 15 meters below the surface that was struck. The longest known fulgurite (over 4.9 meters) is from northern Florida, U.S.A. The colors of fulgurites vary from black or tan to green or translucent white depending on the composition of the sand they are formed from. Some interesting information about this mineral is found on the website of the Mineralogical Research Company: FULGURITES (website 3). The name Fulgurite comes from the Latin word FULGUR meaning lightning (Figure 3). Lechatelierite var. Fulgurite is the varietal name given to fused Quartz, which has been fused by the action of lightning striking the Earth and locally melting the sand. Rock Fulgurites (Figure 4) are formed when lightning strikes the surface of a rock, melting and fusing the surface, and sometimes the interior of the rock. This website introduces few more related terms and explains as follows: “In addition to having been found in terrestrial Fulgurites, Lechatelierite (natural fused Silica, Si02) has also been identified in the glass-like particles found in Tektites. This includes Australites, Darwin Glass, Indochinites, Javanites, Libyan Desert Glass, Moldavites, Philippinites, Bediasites, Muong Nong-type glass, and Aouelloul crater glass (Impactite). Lechatelierite is not present in Obsidian, a terrestrial glass-like material associated with volcanic activity.” Figure 3: A thunderbolt (source: http://webecoist.momtastic.com/2009/11/03/fulgurites- high-glass-digs-where-lightning-goes-to-die/ ) 3 Open Access e-Journal Earth Science India - www.earthscienceindia.info Popular Issue, V (IV), October, 2012, p. 1-8 Figure 4: Rock fulgurite (circled in white) found on quartzite at the summit of Mount Raymond in the Wasatch Range, Salt Lake County, Utah. Hammer for scale. (Source: website 1). There is a record of fossilized fulgurite from the Permian rocks of Scotland (website 4; Figures 6 and 7). This website also contains interesting information about the man-made fulgurites. According to the website ‘About.com geology’ (website 5) similar minerals are formed besides lightning, for example : “ Sand swept up in the Trinity atomic-bomb test, in the New Mexico desert, melted and rained down on the test site forming a green glass called trinitite. And impacts by meteorites can produce fused sand and other melted bits known collectively as tektites. The clear green variety called moldavite is the most famous of these. ” In India, Jaikaran (1998) reported the occurrence of fulgurites from Udhiyur in Periyar District of Tamil Nadu. Saikia et al. (2008) conducted Fourier-transform infrared spectroscopic characterization to study naturally occurring glassy fulgurite from Garuamukh near Nagaon town in Assam and suggested its implications in understanding the thermodynamic properties of naturally occurring glasses formed by shock metamorphism. Geological Significance of fulgurites: Rafael Navarro-González recognized that fulgurites contain samples of air in their bubbles and should preserve the gases for geologically interesting periods of time. Navarro- González et al. (2007) studied around fifteen thousand years old fulgurite from the Libyan Desert. They analyzed the gas from fulgurite bubbles and measured luminescence using heat treatment (thermoluminescence) and presented new information pertinent to ancient climate and paleoecology. They concluded as follows; 4 Open Access e-Journal Earth Science India - www.earthscienceindia.info Popular Issue, V (IV), October, 2012, p. 1-8 1. Nitric oxide (NO) was found in the bubbles. This supports evidence that NO forms in the lightning channel, not from shock waves nearby. 2. The bubble gases come from the soil and its organic content, not the atmosphere. The carbon atoms match the isotopic profile of C4 plants common in hot dry places. Since lightning is absent from this part of the Sahara today, the fulgurites testify that the area once had a climate like the Sahel region to the south, where lightning and grasslands are common today. 3. The luminescence dating provided an age of about 15,000 years that is latest Pleistocene Epoch. Until this study, there was little hard evidence that lightning had even existed in the geologic past, let alone any knowledge of its patterns in time and space. Figure 5: Sand fulgurite (source: http://en.wikipedia.org/wiki/Fulgurite ) This study discloses new facts about the environment of the ancient Sahara Desert and the chemical changes during the interaction between atmosphere and lightning. It also shows that fulgurites are archives of ancient lightning, atmospheres and ecology. Crespole et al. (2009) described and analyzed the glass of the fulgurite from Torre de Moncorvo in Portugal. This fulgurite showed a large quantity of small vesicles and partially melted quartz along with fractured crystals of cristobalite and quartz. They described two types of glass that were formed in two phases of incongruent melting. The chemistry of these glasses indicates that they were formed exclusively from native granitic material. 5 Open Access e-Journal Earth Science India - www.earthscienceindia.info Popular Issue, V (IV), October, 2012, p. 1-8 Carter et al. (2010) carried a Raman Spectroscopic study on several fulgurites that revealed several forms of crystalline and fused silica as well as the presence of polyaromatic hydrocarbons found in an interfacial zone of a glass bubble. They reported on a molecular spectroscopic study of the composition of a fulgurite that revealed new information about little-understood geological markers of palaeoclimatic conditions. They also suggested that the fulgurite samples were subjected to a range of temperatures during their formation. The preservation of an early record of organic material inside glasses synthesized in developing evolutionary systems from electric storms provide yet another novel example of an extreme environmental scenario that needs to be considered in an astrobiological context as well as a terrestrial one. Pasek et al. (2012) provide the latest information on fulgurite morphology, a new classification scheme and more evidence for their formation.
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