Gualtieri A. F. The aid of X-Ray powder diffraction to the characterisation and treatment of asbestos containing materials 1-11
ABSTRACT
- Fibrous asbestos
minerals have been identified as priority substances for risk reduction and
pollution prevention. Because of the well known hazardous effects associated
with past occupational exposures to asbestos and because of its widespread use
in commerce, exposures to asbestos present a general health hazard. Therefore,
the identification and quantification of asbestos in bulk materials which are
still sited in a number of plants and public buildings is fundamental for a
proper plan of social prevention and general intervention. X-ray powder diffraction
is considered an effective tool of investigation of bulk materials with high
statistical significance. The combined Rietveld-RIR method, has been successfully
applied for the quantitative determination in the past of asbestos in bulk materials
such as insulating cements, mixed asbestos-slag wools, contaminated soils, and
others.
The University of
Jussieu in Paris has been partly evacuated because the framework of the building
is composed of an asbestos rich material. This paper reports the description
of the characterisation of that material and a possible plan of intervention
for the treatment of the hazardous material in situ.
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ABSTRACT - Spinel-bearing lherzolite and harzburgite mantle xenoliths from central Sardinia (Italy) contain glassy patches with clinopyroxene and spinel relicts together with euhedral crystallites of olivine, clinopyroxene and spinel. Although texturally uniform, the glass may be chemically distinguished into two groups: the first type with low K2O (mean 0.07 ± 0.05 wt%) and TiO2 (mean 0.68 ± 0.12 wt%; LKT-type), and the second type with high K2O (mean 2.52 ± 0.82 wt%) and TiO2 (mean 3.14 ± 0.35 wt%; HKT-type). All glass compositions are quartz-normative. Rare phlogopite laths are enclosed in olivine or orthopyroxene crystals. The following mass balance equations have been obtained both for HKT- and LKT-type glasses:
6.9 Cpx(1)
+ 0.6Sp(1) => 3.5Cpx(2) + 0.6Sp(2) + 0.1Ol(2)
+ 1.0Glass (LKT)
and
7.9 Cpx(1)
+ 0.5Sp(1) + 0.7Phl(1) => 3.8Cpx(2) + 0.6Sp(2)
+ 0.1Ol(2) + 1.0Glass (HKT)
where the subscript (1)
and (2) represent primary (reactant) and secondary (product) phases, respectively.
Clinopyroxene + spinel ± phlogopite are expected to have melted incongruently
to yield olivine, clinopyroxene and spinel. This suggests that the glasses are
not the product of metasomatic processes, but derive by decompression melting
of mantle xenoliths, probably after the incorporation in the host lava. Other
evidences of early stages of partial melting come from the relatively abundant
spongy-textured clinopyroxene. Recent experimental studies (Raterron et al.,
1997) evidence the incongruent partial melting of clinopyroxene at mantle depth
several hundreds degrees below its conventional solidus temperature. Metasomatic
processes in the Sardinia lithospheric mantle account for the origin of phlogopite
in the xenoliths.
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ABSTRACT
- The flux growth
methods, with Na2B4O7 as flux, was successfully
used to produce high-quality single crystals of spinel with compositions corresponding
to solid solutions of spinel s.s. (MgAl2O4) – magnesioferrite
(MgFe3+2O4) and spinel s.s. – hercynite
(Fe2+Al2O4). Some intermediate terms of spinel
s.s. – franklinite (ZnFe3+2O4) solid
solution were also producted. Low cooling rates (1-4°C/h) and linear temperature
profiles were applied in the thermal interval 1200-800°C. Thermal runs were
performed in air or in an H2/CO2 reducing atmosphere.
The resulting crystal underwent microchemical, structural and spectroscopic
characterisation for later thermodynamic and kinetic studies of spinel order-disorder
with temperature. Both the miscibility gap between spinel s.s. and magnesioferrite
and the complete solid solution between spinel s.s. and hercyte were
experimentally confirmed. The constant presence of minor ferric iron was found
in hercyte, in spite of the highly reducing conditions imposed during crystal
growth.
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Tommasini S., Polli G. and Ghezzo C. Trace element inferences on the evolution and genesis of the Monte Pulchiana leucogranites, northern Sardinia, Italy 53-67
ABSTRACT
- The Monte Pulchiana
leucogranites belong to the Sardinia-Corsica batholith and were emplaced during
the post-collisional phase of the Hercynian orogeny. They consist of multiple
coalescent intrusions cut by numerous aplitic dikes and outcrop along a surface
of about 40 Km2. At least two different parental magmas have been
distinguished on the basis of their geochemical characteristics. The evolution
of main group of the Monte <pulchiana leucogranites (MGL) can be accounted
for by crystal fractionation process of two extreme mineral assemblages. The
discrimination between evolutive and genetic processes allows to set constraints
on the geochemistry of the source(s) of the Monte Pulchiana leucogranites. Geochemical
andphysical arguments provide evidence for a heterogeneous, andesitic-like composition
source for the Monte Pulchiana leucogranites. The origin of this andesitic crust
be found in the magmatic activity which took place in the Sardinia and Corsica
islands in the Ordovician, prior to the onset of the Hercynian orogeny. The
source heterogeities could have developed because of either intrinsic or extrinsic
processes. The former concern differentiation of the andesitic magmas, whereas
the latter concern the percolation of the huge amount of the late-tectonic monzogranitic
melts en route to the sourface, throughout the upper portion of the andesitic
crust. This resulted in the formation of a mixed, net-veined crustal source
which subsequently experienced a partial melting process during the adiabatic
upwelling of the Sardinia-Corsica basement occurred in the post-collisional
phase of the Hercynian orogeny.
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ABSTRACT
- Melt inclusion analysed
were carried out on quaternary rhyolitic rocks from Roccastrada volcano (Tuscany,
central Italy). The data confirm the anatectic origin for the magma that gave
rise to the Roccastrada volcanism and evidenced no involvement of basic component
in the petrogenesis of these melts. Similar compositions of melt inclusions
trapped in phenocrysts and of residual glass matrix of Roccastrada rhyolites,
suggest that these melts did not undergo to important differentiation processes
after their generation. Quartz, sanidine, plagioclase and cordierite crystallized
from peralominous melts, at temperatures in the range of 755-820°C, and at pressure
of about 150-180 MPa.
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Sucha V., Kraus I., Samajová E. and Puškeloá L. Crystallite size distribution of kaolin minerals 81-92
ABSTRACT
- The new BWA (Bertaut-Warren-Averbach)
technique for measurement of mean crystallite thickness and thickness distributions
of phyllosilicates was applied to a set of kaolin minerals. We analyzed 39 kaolins
from the western Carpathians and from other main world deposits, which are of
residual, sedimentary, or hydrothermal origin. We show that the BWA technique
can be successfully applied to both kaolinites and halloysites. Three different
shape types of thickness distribution were found – longnormal, asymptotic and
polymodal – among the studies set of samples. Mean thickness data were compared
with kaolinite crystallinity indices (Stoch index and Hughes and Brown index)
and good correlations were found only for unimodal distributions. These crystallinity
indices are not suitable for characterisation of kaolin mixtures.
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