Obsidian in the Aegean

1965 ◽  
Vol 60 ◽  
pp. 225-247 ◽  
Author(s):  
Colin Renfrew ◽  
J. R. Cann ◽  
J. E. Dixon

Obsidian to the Greeks was no more than a semi-precious stone, black and shiny, suitable for mirrors or exotic ornaments. But to their predecessors in the Aegean through five millenia it was an important raw material for the manufacture of tools and weapons. Sharper and more abundant than flint, more easily worked and cheaper than copper, it was not displaced entirely even by the use of bronze, which was always an expensive material, there being no source of tin in the Aegean. Only when knowledge of iron-working was brought to the Aegean coasts did obsidian fall from its position as an important raw material to that of a curiosity.Huge quantities of obsidian are to be found lying about the surface of most prehistoric sites in south Greece—any farmer or shepherd will tell of the ‘little razors’ to be found on his land. But its occurrence in nature is very unusual since it is found exclusively in regions of recent volcanic activity, and then only when certain conditions exist, such as a high silica content in the lava of the volcano. Every single piece found in mainland Greece had to be imported from overseas, a process implying competent geological knowledge, skill in sailing and navigation, and perhaps social organization, to a considerable degree. It is the earliest trade in the world for which we have concrete evidence.

2017 ◽  
Vol 106 (2) ◽  
pp. 510-520 ◽  
Author(s):  
Basam A. E. Ben-Arfa ◽  
Hugo R. Fernandes ◽  
Isabel M. Miranda Salvado ◽  
José M. F. Ferreira ◽  
Robert C. Pullar

2019 ◽  
Vol 342 ◽  
Author(s):  
Jean Gérard ◽  
Sébastien Paradis ◽  
Bernard Thibaut

Variability in the chemical composition of 614 species is described in a database containing measurements of wood polymers (cellulose, lignin and pentosan), as well as overall extraneous components (ethanol-benzene, or hot water extracts and ash, with a focus on silica content). These measurements were taken between 1945 and 1990 using the same standard protocol. In all, 1,194 trees belonging to 614 species, 358 genera and 89 families were measured. At species level, variability (quantified by the coefficient of variation) was rather high for density (27%), much lower for lignin and cellulose (14% and 10%) and much higher for ethanol/benzene extractives, hot water extractives and ash content (81%, 60% and 76%). Considering trees with at least five different specimens, and species with at least 10 different trees, it was possible to investigate within-tree and within-species variability. Large differences were found between trees of a given species for extraneous components, and more than one tree should be needed per species. For density, lignin, pentosan and cellulose, the distribution of values was nearly symmetrical, with mean values of 720 kg/m3 for density, 29.1% for lignin, 15.8% for pentosan, and 42.4% for cellulose. There were clear differences between species for lignin content. For extraneous components, the distribution was very dissymmetrical, with a minority of woods rich in this component composing the high value tail. A high value for any extraneous component, even in only one tree, is sufficient to classify the species in respect of that component. Siliceous woods identified by silica bodies in anatomy have a very high silica content and only those species deserve a silica study.


2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Juan Espindola ◽  
Osama M. Selim ◽  
Ryoichi S. Amano

Abstract The increase in the production scale of chicken causes an increment in the produced manure. Chicken manure is considered an excellent soil amendment due to the high nitrogen and phosphorous content. However, the high production of manure exceeds the soil requirements. Rice husk is a by-product of rice production. Approximately one hundred forty million tons of rice husk is produced per year worldwide. There are several ways to manage rice husk such as animal bedding, direct combustion, or as a soil fertilizer. The husk's ashes are suitable for construction or as reinforcing material due to the high silica content. However, rice husk has a low volatile matter and high silica content, which makes processes like direct combustion inefficient. Thermochemical processes (such as pyrolysis and gasification) are effective ways to manage waste. The present study investigates the co-pyrolysis of chicken manure and rice husk. The experiments were conducted in a non-isothermal gravimetrical analyzer using nitrogen at a flowrate of 100 ml/min at three different heating rates (5, 10, and 15 °C/min). The degradation of individual biomass and biomass blends is investigated. The kinetic parameters are calculated using the Friedman method. Results show a positive synergetic effect for mixing ratios greater than 20% rice husk. The mixing ratio of 40% of rice husk manifested the best performance among all blends. This mixture showed the minimum energy of activation (90.2 kJ/mol). Also, the 40% rice husk mixing ratio showed maximum conversion when compared with chicken manure's conversion.


2005 ◽  
Vol 34 (5) ◽  
pp. 672-673 ◽  
Author(s):  
Sirilux Poompradub ◽  
Shinzo Kohjiya ◽  
Yuko Ikeda

2013 ◽  
Vol 315 ◽  
pp. 724-727 ◽  
Author(s):  
Y. Tijjani ◽  
B. Onyekpe ◽  
I.A. Rafukka

The characterization of Chalawa river sand with its suitability for foundry applications has been investigated. Chemical and sieve analyses and Green permeability were determined for the sand via standard procedure. Based on the result of the chemical and sieve analyses and permeability (the sand by its high silica content and low alkali fluxes) it needs small amount of binder, has moderate refractoriness and therefore, can be employed in foundry applications.


2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Murad Alsawalha ◽  
Elaref Ratemi

This current article demonstrates how X-ray fluorescence spectroscopy (XRF) was employed to reveal the major constituents of a sample of natural grey Saudi kaolin. The XRF results showed that it contained 52.90 wt.% silica together with 14.84 wt.% alumina. Additionally, this paper presents a study on the effect of holding times (i.e., 6, 12, 18, and 24 h) using pyrrole adsorption and methylbutynol test reaction (MBOH) on the Saudi grey kaolin (raw material). Temperature-programmed desorption of pyrrole (pyrrole-TPD) results indicated that increases in thermal conductivity detector (TCD) signals are directly proportional to increases in the heat activation holding time. Notably, a raw Saudi grey kaolin sample heated at a holding time of twenty-four hours resulted in the most intense TCD signal. Further, the MBOH transformations produced 3-methyl-3-buten-1-yne (MBYNE), as the main product, indicating the dehydration of MBOH due to the acidic sites of Saudi grey kaolin. The basic catalysis route was operative at the beginning of the reaction as acetone was observed only during the initial thirty-five minutes of the reaction then later dispersed entirely. Its disappearance is attributed to the high silica content of the test sample.


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