Natural Glasses

Abstract

On Earth, natural glasses are typically produced by rapid cooling of melts, and as in the case of minerals and rocks, natural glasses can provide key information on the evolution of the Earth. However, we are aware that natural glasses are products not solely terrestrial and that the formation mechanisms give rise to a variety of natural amorphous materials. On the Earth´s surface, glasses are scarce compared to other terrestrial bodies (i.e. Moon), since the CONTENTS-QUENCHED GLASSES 1.1 -Volcanic glasses Applications: alteration of natural glasses as analogue of nuclear waste glasses 1.2 -Lunar glasses 2 -IMPACT GLASSES 2.1 -Tektites and microtektites 2.2 -K-Pg (KT) spherules 2.3 -Younger Dryas (YD) event 2.4 -Enigmatic impact glasses 2.4.1 -LDG -Libyan Desert Glass 2.4.2 -Darwin glass 2.5 -Fulgurites 3 -OBSIDIAN 3.1 -Hydrated and altered obsidians 4 -OTHERS 4.1 -Glasses from nuclear explosion 4.2 -Friction melts 4.3 -Bioglasses 5 -Insights into the structure and properties of glasses -ConclusionsTo date, four main groups of tektites, associated with separate impacts and strewn fields (SF), are known (e.g., [68][69][70][71]): the North American, the Ivory Coast, the central European and the Australasian (Fig. 10). The source craters have been located for three of the four tektite strewn fields, based on geographic location, geochemical evidences, and composition [72][73][74].The oldest strewn field is the North American (NA) field of ~ 35.5 Ma age associated with the ~ 40 km wide Chesapeake Bay impact structure [75] and includes Bediasites, Georgianites, Barbados and Cuba tektites, respectively found in Texas, Georgia, Barbados and Cuba (Fig. 10). The central European (CE) or moldavite strewn field of 14.4 Ma age is associated with the Ries crater of about 24km in diameter (Nördlinger Ries, Bavaria, D).There is another impact crater, the Steinheim crater, ~ 3.8 km in diameter, located about 42 kilometers west-southwest from the centre of Ries. These two craters are believed to have formed nearly simultaneously by the impact of a binary asteroid [76]. The Ivory Coast (IC) tektite strewn field is associated with the 1.07 Ma old Bosumtwi crater (10.5 km diameter, Ghana, Africa). The youngest SF, of about 0.8 Ma, is the Australasian one, for which no source crater has been identified so far. Tektites of the Australasian strewn field (AA) include australites, thailandites, indochinites, philippinites and javanites and spread from the southeastern region of Asia down to Australia (Fig. 10). Recently, glass spherules (microtektites) were discovered on the Victoria Land Transantarctic Mountains (Antarctica) and there is clear evidence [69,77,78] that these microtektites represent a major southeastward extension of the Australasian strewn field.Even if no source crater has been discovered yet, several authors suggest a location for the AA crater in the Indochina region (see [79][80][81][82]).

Non-Magmatic Glasses

“…Volcanic glasses produced upon rapid cooling of basaltic melts are called sideromelane, but they also occur as volcanic ash, fibers and teardrops (i.e. Pele's Hair and Pele's Tears) and more rarely form solidified foamreticulite (Cicconi & Neuville 2019). Obsidian glass was first described by Pliny The Elder's Natural History with the name of "obsiana", so called because its similarity to a very dark stone found in Ethiopia by Obsius.…”

“…dragonglass, after the fantasy drama television series Game of Thrones). Obsidians are generally subalkalic rhyolitic with an average composition of about (wt.%) 72-77% SiO2, 10-15% Al2O3, 1-2% FeOtot, 7-10% alkali (K2O + Na2O), 0.5-2% alkali-earth (CaO + MgO) (Cicconi & Neuville 2019 and references therein). The glass-forming processes of obsidian melts are strongly influenced by the content, size and shape of microlites (Castro et al 2002), and by the contents of volatile components (such as water, fluorine and chlorine, sulphur and carbon oxides (Carmichael 1979;Heide & Heide 2011), and small variations in volatile contents can cause important changes in the flow dynamics of obsidian melts.…”

“…Several siliceous marine organisms exhibit discontinuous, three-dimensional frameworks of short chains of SiO4 tetrahedra, bonded with apical hydroxyls. The low-temperature hydrated variety of silica, opal (SiO2*nH2O), is a biomineral, and displays different arrangements of amorphous SiO2, water, and cristobalite, and/or tridymite (Cicconi & Neuville 2019). Depending on the arrangements, it is possible to distinguish three opal types: i) opal-C (cristobalite); ii) opal-CT (cristobalite and tridymite); iii) opal-A (X-ray-amorphous opal).…”

Effect of Ti4+ on the structure of nepheline (NaAlSiO4) glass

“…Ti is also found in more complex natural glasses on the order of ~1 wt% (for example, tektites and some basaltic glasses) and up to ~16 wt% in lunar glasses (Cicconi and Neuville, 2019), though in lunar glasses, Ti can be present as Ti 3+ due to low oxygen fugacity (Krawczynski et al, 2009). Additionally, fulgurites formed in mafic or ultramafic rock can have increased amounts of TiO 2 in addition to being silica-rich.…”

A Corning perspective on the future of technical glass in our evolving world

“…Obsidian, a volcanic glass, formed from rapidly cooled lava exuded from beneath the surface of the earth, was most certainly available as a potential tool or object of interest to humanity, well before humans developed processes to synthesize glass. Not surprisingly, obsidian generally consists of silicon, oxygen, aluminum, sodium, and potassium, 1 which are abundantly available elements within the earth's crust, and are often used in mineral or oxide form (e.g., sand, alumina, soda ash, and potassium carbonate) as raw materials for the production of glass today. 2 The production of glass dates back at least 3600 years ago to Mesopotamia, Egypt, and Syria.…”