The clay fraction was made up of smectite, amorphous material, cristobalite
and goethite, which contribute to the intense shrink-swell processes of these soils.
The elimination of cristobalite
inversion in the clay body.
Acid sulfate alteration is observed near to the La Olleta crater in the NRV; there, a paragenesis of amorphous silica, quartz, sulfur, alunite, mercallite and cristobalite
was identified by XRD.
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Other quartz clasts exhibit a so-called 'ballen texture' which may indicate that they were cristobalite
, before reverting to quartz at lower temperatures.
indicated the presence of all three regulated silica polymorphs (quartz, cristobalite
, and tridymite) at varying concentrations throughout the mesa .
The ash also contained large amounts of cristobalite
, a form of silica which can cause the lung disease silicosis.
A group of researchers, led by Peter Baxter of the University of Cambridge, has found that the ash ejected by the Soufriere Hills volcano since 1995 contains a surprisingly high concentration of cristobalite
, which is a mineral known to cause the lung disease silicosis.
The occurrence of possible processes of conversion of primary aragonite into calcite and primary opaline silica via cristobalite
and tridymite into quartz remains problematic, although the locally survived coexistence of quartz and two other modifications refers to this possibility.
Changes over 4% are seen as a result of either tridymite or cristobalite
The microcrystalline varieties comprise opal-C (rare) and opal-CT (quite common), which are basically poorly crystallized cristobalite
(C) with more-or-less tridymite-like (T) stacking.
Also common are columnar crystals of pseudobrookite, niobian rutile, cristobalite
, magnetite and cryptocrystalline cassiterite.