1, silica, as expected, goes through the alpha-beta phase transition at 1,045F (580C) and starts undergoing a cristobalite
transition at 2,410F (1,300C).
Then, in 1994, OSHA identified crystalline silica as one of a few top-priority safety and health hazards, and, two years later, the International Agency for Research on Cancer concluded that "crystalline silica inhaled in the form of quartz or cristobalite
from occupational sources is carcinogenic to humans.
That lower level would also apply to two other forms of crystalline silica: cristobalite
The proposed 50 [micro]g/m3 PEL for quartz matches 0SHA's existing threshold for two other forms of respirable crystalline silica, cristobalite
and tridymite, in general industry workplaces.
Once most available stoneware clay bodies reach the stoneware temperature range (cone 8 to 10), micro fine silica in the clay body forms cristobalite
(a form of silica) from silica that did not become part of the glossy structure of the clay.
2] such as quartz, cristobalite
and opal), silicates (albite.
Typical high temperature non magnetic minerals found in pyrometamorphic rocks associated with coal combustion appear to include several Fe and Al rich clinopyroxene, melilita, cristobalite
, tridymite, mullite, cordierite and fayalite solid solutions, as well as glass (Foit et al.
Occupational exposure and analysis of microcrystalline cristobalite
Laboratory experiments indicate that cristobalite
can be more toxic than quartz, a known cause of silicosis in workers with long-term exposure to silica dusts, but the reason for cristobalite
's increased toxicity is not known, says Sparks.
and trydimite, considered to be the more toxic forms of silica, are thermal transformation forms most often found in steel foundries and in furnace and ladle relining operations where silica is exposed to significantly higher temperatures.