Fulgurites
Fulgurite is from the Latin fulgur meaning lightning and fulgarites are sometimes called petrified lightning (dictionary.com, 2007). This is because when lightning strikes a surface such as a rock or sand, the intense heat causes the material to metamorphose along the entire distance that the bolt struck it. Sometimes this can cause spectacular formation that stick out of the sand in deserts that can be quite tall. All lightning that strikes the ground are capable of forming a fulgurite, but most do not because they strike in less than ideal places. There are two kinds of fulgurites, the sandy kinds and the rocky kinds. The sandy are the most common and they have a glassy interior due to their rapid cooling. They are the tube shaped fulgurites. The rocky fulgurites typically appear at the top of mountains where there are repeated lightning strikes. These fulgurites do not form their own specific tubes, they instead tend to form in fractures that the rock already had or on the surface of the rock (Ege, 2005). Since the fulgurites form glass, which happens to be very resistant to weathering, fulgurites can last for millions of years. This is why the Sahara Desert is a hot bed for fulgurite hunters. The area does not receive much in the way of lightning activity now but apparently it did in the past and the entire desert is pock marked with sand fulgurites that are roughly 250 million years old (Rakov, 2007). The age of some of the fulgurites has allowed scientists to study the gases that are trapped in the hollow space between the melted sand. This is an important tool for paleoclimatologists as it provides physical data for the gas content of the atmosphere (Simons, 2007).
This fragile sand fulgurite was the result of a lightning strike in 1993 at Camp Blanding, Florida. The color and type of resulting fulgurite depends upon the sand found in this beach area. This particular area produced the world's longest fulgurite, 17 feet, buried and excavated, it was formed around a power cable when lightning was tiggered as a part of an experiment on the effects of lightning on underground power cables. Image taken from http://plaza.ufl.edu/rakov/figures/2.jpg in a V. Rakov article, (plaza.ufl.edu/rakov/figures/GAS.pdf.
The photographer and author was Dr. Vladimir A. Rakov is a co-director of International Center for Lightning Research and Testing (http://www.ece.ufl.edu/research/centers/iclrt.html) at the University of Florida at Gainsville interested in studying lightning, atmospheric electricity, and lightning protection. He co-authored an encyclopedia of lightning, Lightning: Physics and effects (plaza.ufl.edu/rakov/LPE/LPE.html).
This is a fulgurite on a pink rhyolite. The photographer stated:
They look like somebody melted a green Coke bottle and dribbled the glass on the rhyolite. What happened is that the event reduced the iron from the pink Fe2O3 to green FeO. We don't know if other elements outgassed; it would be fun to do a chem analysis of the green stuff and the red stuff and see if anything is missing. Rhyolite comes out of the ground pretty hot so it has already outgassed once in it's history but I think lightning is a lot hotter.
Quote and image taken from http://www.diggles.com/shastina/020622-1487_Fulgurite.jpg and a photograhic diary by Mike Diggles team trip to the summit of Mt. Shastina near Weed, CA. Michael Diggles was part of a team involved in the The Sierra Nevada Ecosystem Project (pubs.usgs.gov/dds/dds-43/, which was coordinated by the University of CA at Davis.
Shock Quartz
Shock quartz is a metamorphosed variety of quartz. It occurs in high pressure, but low temperature metamorphism. It was first discovered by American scientists in the 1940s after the testing of this nation's first atomic weapons in the deserts of the Southwest. The quartz that the bomb had ejected from the detonation site had something very wrong with it when it was inspected. The entire crystalline lattice had shifted. The lattice is moved to the side in relationship to the planes of the atomic structure of a typical quartz mineral. This shock quartz as it was later named was thought to be an anomaly, but then it began to show up in the rock record all over the world (Bigelow, 2001).
Image shown right is a photomicrograph or thin sectioned sample viewed under a microscope. The image was taken from a webpage featuring the research work of Jared R. Morrow of San Diego State University, San Diago, California, http://www-rohan.sdsu.edu/~jmorrow/interests.htm
Image left is a color photomicrograph or grain sample viewed under a microscope. The image was taken from esp.cr.usgs.gov/info/kt/fig6_color.jpg, which was found within the Discussion of K/T Boundary (esp.cr.usgs.gov/info/kt/boundary.html. The caption specifically stated:
Photomicrograph by G.A. Izett of a 0.21-mm diameter shock metamorphosed quartz grain from the Starkville South site. The grain is mounted in index oil on the needle (dark part of photograph) of a spindle stage. The two sets of planar lamellae that are prominent in the photograph are strong evidence of impact origin as no comparable lamellae have been observed in rocks of volcanic origin, only those related to impact and underground atomic explosions (Izett, 1990). Shocked quartz grains have been observed in K-T boundary layers worldwide.
The article, which included the above image, was detailing evidence for the K-T boundary or the boundary between the Cretaceous (K) and Tertiary (T) geologic time periods in the Raton Basin found in Colorado and New Mexico, USA. Thus, the presence of shock quartz here and in the Yucatan Peninsula area indicated the occurrence of a major meteorite impact event. Eventually enough data worldwide was collected that indicated a large meteorite impact event occurred just off the coast in the present day Yucatan Peninsula area around 65 million years ago, which is the geologic time separating the Cretaceous and Tertiary time. The theory is that the meteor that struck the earth was an impactor dense enough and traveling fast enough to eject several million cubic tons of the shock quartz and other crustal materials into the atmosphere, which in turn spread the fine debris around Earth thanks to the prevailing winds. Results were devastating for life on Earth at that time as these K-T boundary materials provide convincing evidence in support of an impact as the cause for the mass extinctions at the end of the Cretaceous (Bohor et al., 1987).
Sources
- Bigelow, P. 2001. What is “Shocked Quartz”? WWW URL:
www.scn.org/~bh162/shocked_quartz.html, accessed on October 14, 2007.
- Bohor, B.F., Modreski, P.J., & Foord, E.E. 1987. Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution. Science vol. 236, no.4802, p. 705-709. Abstract on WWW URL: www.sciencemag.org/cgi/content/abstract/236/4802/705.
- Ege, C. 2005. What are Fulgurates and where can they be found? Utah Geological Survey: Glad You Asked article, Survey Notes, v. 37 no. 1, January 2005. WWW URL geology.utah.gov/surveynotes/gladasked/gladfulgurites.htm, accessed on
October 14, 2007.
- dictionary.com. 2007. Fulgurite. WWW URL: dictionary.reference.com/browse/fulgurite, accessed on October 14, 2007.
- Pillmore, C.L., Nichols, D.J., & Fleming, R.F. 1999. Discussion of K/T Boundary. WWW URL: esp.cr.usgs.gov/info/kt/boundary.html. This chapter found within: Field guide to the continental Cretaceous-Tertiary boundary in the Raton basin, Colorado and New Mexico: Geological Society of America, Field Guide 1, WWW URL: esp.cr.usgs.gov/info/kt/. Online guide adapted from Pillmore, Nichols, and Fleming, Cretaceous-Tertiary boundary studies in the Southwest, WWW URL: esp.cr.usgs.gov/research.html.
- Rakov, V.A. 1999. Lightning Makes Glass. WWW URL: plaza.ufl.edu/rakov/Gas.html, accessed on October 14, 2007.
- Simons, P. 2007. Sands of the Sahara reveal ancient grasslands. The London Times pp. 77.
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Webpage created November 2007; latest update December 3, 2007. Copyright Greg Gantz.
