Results 211 to 220 of about 21,971 (257)

Pyroclastic rocks in the Cnapan Breaca felsite, Rhum

Geological Magazine, 1985
AbstractThe Cnapan Breaca felsite sheet contains strongly devitrified pyroclastic rocks including welded tuffs. These indicate formation in a high level, surficial or sub-volcanic environment. The gross structure and lithological associations of the sheet are similar to those of some ignimbrites. These observations support a resurgent caldera model for
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Early-stage smectites from pyroclastic rocks of Almería (Spain)

Chemical Geology, 1991
Abstract In the volcanic region of Cabo de Gata (Almeria, Spain) bentonite deposits were formed from pyroclastic rocks. There is evidence that the smectite composition changed from Fe-rich to Al-rich members as the degree of hydrothermal alteration increased. Because true initial stages of alteration do not occur in this region, artificial hydrolysis
E. Caballero, E. Reyes, F. Huertas, J. Linares, A. Pozzuoli   +4 more
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Altered pyroclastic rocks in South African iron-formation

Economic Geology, 1966
Hundreds of layers composed dominantly of stilpnomelane occur in thick extensive iron-formation in the Transvaal system in South Africa. Examination of thin sections reveals that many of these layers contain axiolitic shard-like structures, suggesting that they are altered pyroclastic material, presumably water-laid tuffs.
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Pyroclastic rocks and calderas associated with strongly peralkaline magmatism

Journal of Geophysical Research: Solid Earth, 1984
Strongly peralkaline volcanic complexes tend to be shieldlike due to coalescence of low‐viscosity lavas from numerous vent areas and blanketing by pyroclastic flows and falls. Dense welding and rheomorphism commonly mask the nature of pyroclastic units; welded pumice falls are common.
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MICROSTRUCTURE AND POZZOLANIC ACTIVITY OF SOME PYROCLASTIC ROCKS FROM SARDINIA (ITALY)

1991
Pozzolanic cements have been used for millennia as building materials, but they can also satisfy modern requirements, namely low energy consumption in production and durability. This article describes work which studied, by chemical, physical, petrographical and technological means, the pozzolanic characteristics of four Oligocene-Miocene calcalkaline ...
SISTU, GIOVANNI, Atzeni C., Massidda L., SANNA, ULRICO UMBERTO MARIA   +3 more
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Recognition and Significance of Pumice in Marine Pyroclastic Rocks

Geological Society of America Bulletin, 1969
Pumice is abundant in many ancient sequences of marine pyroclastic rocks and is regarded as important evidence that contemporaneous, or nearly contemporaneous, volcanic activity was the source of at least some of the fragmental debris. The pumice in many such sequences of rocks, however, is easily overlooked, chiefly because most marine pyroclastic ...
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Stratigraphy of Jurassic pyroclastic rocks in the Transantarctic Mountains

Journal of African Earth Sciences, 2000
Abstract Jurassic pyroclastic rocks cap the Antarctic Gondwana sequence and document an important event in the evolution of the continent. The Hanson Formation, which crops out in the central Transantarctic Mountains, consists of ca 240 m of silicic tuffs, tuffaceous sandstones, and subordinate quartzose sandstones of probable Early Jurassic age.
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Experimental Evidence of Non-Linear and Creep Behaviour of Pyroclastic Rocks

1994
An analysis of the mechanical behaviour of pyroclastic rocks is discussed in this paper, with particular evidence to non-linear and creep behaviour. This topic is treated presenting experimental results obtained on Neapolitan tuffs at the University of Naples.
AVERSA S., EVANGELISTA, ALDO
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Application of X-Ray Microtomography in Pyroclastic Rocks

2019
Earth scientists gather geological information from rocks in order to understand the geological processes better. It is compulsory to examine rocks in detail for reliable geological deductions. Petrographical analyses, which inspect the rocks in terms of their physicochemical composition and texture, represent the primary step for accurate geological ...
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Geotechnical characteristics of ignimbrite: A soft pyroclastic rock type

Engineering Geology, 1993
Abstract The ranges of a variety of geotechnical properties encompassed by the ignimbrite lithology are established. Ignimbrites are of low density (1212–1928 kg m −3 ) and high porosity (18–51%), are very weak to weak in compression (0.23–54 MN m −2 ), have low tensile strength (0.12–7.1 MN m −2 ) and cohesion (0.06–9.0 MN m −2 ), yet the angle ...
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