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.
It should be noted that none of the analyzed samples contained cristobalite or tridymite
, with all of the reported crystalline content resulting from quartz.
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