Natural glass

Silicon is present in the sun and stars and is a principal component of a class of meteorites known as aerolites. It is also a component of tektites, a natural glass of uncertain origin. 

Obsidian Making tools and decorative objects Natural glass Extremely dense sharp edges conchoidal fracture... 

FIGURE 22 Obsidian in the eastern Mediterranean Sea area. Studying the relative concentration of trace elements in obsidian makes it possible to identify the obsidian and to determine its provenance. Determining the relative amounts of barium and zirconium in ancient obsidian tools and in samples from different sources of the natural glass, for example, made it possible to identify the provenance of obsidian used in eastern Mediterranean Sea area sites (Renfrew and Dixon 1976). 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

The moon rocks brought back to earth are only a tiny sample of the moon s surface, but they are enough to show that some elements common on earth may be rare on the moon, and some that are rare here on earth may be common on the moon. So far, as on earth, oxygen and silicon seem to be the most common lunar elements. Early experiments have found more uranium and less potassium, more titanium and less sodium. Oxygen is strikingly absent from some minerals, but natural glass is far more common than it is on earth. The rare, noble gases are fairly abundant, trapped in little bubbles in the rocks. 

Wolff-Boenisch, D., Gislason, S.R., Oelkers, E.H. and Putnis, C.V. (2004). The dissolution rates of natural glasses as a function of their composition at pH 4 and 10.6, and temperatures from 25 to 74 degrees C. Geochimica et Cosmochimica Acta 68 4843-4858. 

The preceding data, though limited in nature, represent one of the first attempts to measure solid state diffusion rates of alkali elements into the near-surface region of feldspars and natural glasses at low temperature. As such, interesting comparisons can be made with diffusion coefficients and activation energies calculated from numerous high temperature isotope and tracer diffusion studies f 11-181. 

Fibres, nature Glass Carbon Carbon Carbon... 

Especially methods of electron microscopy are important at study of X-ray amorphous substances and polyphase nanomixtures which are distributed very widely in the nature such as agate, bauxite, bitumen, coal, natural glasses etc., as X-ray diffraction is almost useless at analyzing such mostly disordered materials. 

Itq to obtain the Cp versus temperature curve and the maximum Cp value. Repeat this procedure for many different cooling rates (such asq = 0.0001 to 100 K/s). After the maximum Cp value as a function of prior cooling rate is quantified as the calibration curve, measurement of the Cp versus temperature curve upon heating of any natural glass sample with the same composition as the calibration may be used to obtain the cooling rate of the natural glass. 

Byers, C. D., Jercinovic, M. J. Ewing, R. C. 1987b. A study of natural glass analogues as applied to alteration of nuclear waste glass. Report no. NUREG/CR-4842 ANL-86-46, Argonne National Laboratory, 150 p. 

Ewing, R. C. 1979. Natural glasses analogues for radioactive waste forms. In McCarthy, G. J. (ed) Scientific Basis for Nuclear Waste Management I. Plenum Publishing Corp., New York, 57-68. 

O Keefe, J. A. 1984. Natural glass. Journal of Non-Crystalline Solids, 67, 1-17. 

AIELLO (R.), COLELLA (C.) and SERSALE (R.), 1970. Zeolite formation from synthetic and natural glasses. Arne. Chem. Soc. 2nd Int. Zeolite Conf., 48-58. 

---