The micrometre-scale spheres that make up precious opal exhibit some x-ray diffraction patterns that are similar to that of cristobalite, but lack any long-range order so they are not considered true cristobalite.
32.
The micrometre-scale spheres that make up precious opal exhibit some x-ray diffraction patterns that are similar to that of cristobalite, but lack any long-range order so they are not considered true cristobalite.
33.
In the 1930s, long-term occupational exposure among workers in the cristobalite D . E . industry who were exposed to high levels of airborne crystalline silica over decades were found to have an increased risk of silicosis.
34.
The groundmass contains interstitial quartz or tridymite or cristobalite . " Olivine tholeiite " has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass.
35.
To our knowledge, sustained long-term health effects have not been reported in association with exposures to volcanic ash, although there is speculation that the high cristobalite content of the Montserrat ash could lead to silicosis many years later.
36.
After the original work on displacive phase transitions, the RUM model was also applied to understanding the nature of the disordered high-temperature phases of materials such as cristobalite, the dynamics and localised structural distortions in zeolites, and negative thermal expansion.
37.
Dunting also occurs in wares produced from montmorillinite clay bodies due to the volume expansion of cristobalite during its inversion upon cooling . " The release of free silica, takes place in montmorillonite above 950 C, but almost double the silica is released, compared to kaolin.
38.
Evidences of the effect of lightning on rock are the presence of beta-quartz ( T >, called " flashstones " by local diggers ), melted barbed wires ( T > ); furrows in soils and colluvium up to long with the presence of cristobalite, the high-temperature modification of quartz ( ).
39.
At high temperatures, the structure is tetragonal form of cristobalite ( P4 1 2 1 2, No . 92, Pearson symbol " tP12 " ) occurs on cooling below ca . 250 �C at ambient pressure, and is related to the cubic form by a static tilting of the silica tetrahedra in the framework.
40.
Until recently flint was also an important raw material in clay-based ceramic bodies produced in the UK . In preparation for use flint pebbles, frequently sourced from the coasts of South-East England or Western France, were calcined to around 1, 000 �C . This heat process both removed organic impurities and induced certain physical reactions, including converting some of the silica to cristobalite.
