The CheMin identification of tridymite
prompted the team to look at possible explanations for it: "We could solve this by determining whether trydymite in the sediment comes from a volcanic source or has another origin," said Liz Rampe, of Aerodyne Industries at NASA's Johnson Space Center.
Department of the Interior 2003], of which quartz, cristobalite, and tridymite
are the most common.
indicated the presence of all three regulated silica polymorphs (quartz, cristobalite, and tridymite
) at varying concentrations throughout the mesa .
In accordance with the negative correlation between CaO and Si[O.sub.2] the layers of the dominant calcite or silica (quartz, tridymite
, cristobalite) occur, whereas in MgO-rich barren interlayers dolomite may prevail and in certain [P.sub.2][O.sub.5]-enriched beds/interbeds apatite or in [Al.sub.2][O.sub.3]-enriched layers clay minerals occur.
D 600 Amorphous phase, [delta]-[Al.sub.2][O.sub.3] A 1000 Amorphous phase, [delta]-[Al.sub.2][O.sub.3] B 1000 Amorphous phase, anatase, rutile, [delta]- [Al.sub.2][O.sub.3] C 1000 Amorphous phase, anatase, rutile, [delta]- [Al.sub.2][O.sub.3] D 1000 Amorphous phase, [delta]-[Al.sub.2][O.sub.3] A Cristobalite, mullite, 1400 quartz, tridymite
B Cristobalite, mullite, rutile, 1400 tridymite
C Cristobalite, mullite, rutile, 1400 tridymite
D Cristobalite, mullite, 1400 quartz, tridymite
Both cristobalite and tridymite
are polymorphs of nominally pure Si[O.sub.2].
If there is sufficient softening on the surface of the sand grains to create a liquid, tridymite
will be formed.
The X-ray powder diffraction patterns for the starting materials are shown in Figure 4, revealing high-intensity reflections attributed to quartz and kaolinite, although they also showed the presence of albite, crystoballite and tridymite
. The tuff was characterised by the occurrence of an amorphous aluminosilicate (see the broad hump at 2[theta] = 17.5-20.5 [degrees], having a maximum at 2[theta] = ~ 22).
Associated minerals are: tridymite
, fluororichterite, hematite, rutile, aegirine-augite, kinoshitalite and fluorapatite.
Compared with compositions of many other oil shales of the world , including the Estonian Paleozoic kukersite , and graptolite argillite [15-18], the Near East oil shales have specifically high contents of carbonate (calcite), silica (quartz, in places with admixture of tridymite
and cristobalite--unpublished data by the authors) and sulfur .
It is believed this secondary expansion indicates the transformation of the silica from beta quartz to tridymite