Cristobalite

Classification:

Cristobalite is the high-temperature form of SiO₂, which also formes quartz. Cristobalite may crystallize in a fibrous form; compare to silica.

Cas:

14464-46-1

Synonyms/Trade Names:

Calcined Diatomite, Silica.

Chemistry/Composition:

SiO₂ .

Structure:

The structure consists of sheets of six-membered rings of tetrahedra. The tetrahedra of neighboring sheets are linked by apical oxygen atoms. Opposite to tridymite (compare to tridymite), the tetrahedra are not directly superimposed, but rotated around 60. The open Structure can contain large ions.

Crystallographic Constants:

4.970 4.970 6.920 90.000 90.000 90.000.

Crystal Group:

Cubic (temperature 180-270° C); tetragonal (low-temperature form).

Color:

White.

Optical Properties:

nO=1.487 nE=1.484.

Pleochroism:

None and colorless in thin sheets.

Powder Diagram:

4.05 2.49 2.84 3.13 (11-695).

Natural Sources:

Mexico (San Cristobal), and the USA (Yellowstone Park).

Medical Importance:

Key Hazards:

Fibrogenic.

Involved Organs:

Lung.

Exposure/Epidemiology:

Used in ceramics and fireclay production.

Thresholds:	TWA
	mg/m³
Germany	0.15
Switzerland	0.15

Etiology/Pathophysiology:

Crystalline silica induce a focal lung fibrosis, usually seen after 20-40 years of exposure; for details see under the heading silica.

Lung Diseases:

Focal interstitial fibrosis; for details see under the heading silica.

Clinical Presentation:

Patients present with cough, shortness of breath, and dyspnea.

Radiology:

Chest radiographs usually show small nodular densities or diffuse interstitial fibrotic changes in advanced stages.

Lung Function:

Depending on the stage of the disease, usually restrictive changes.

Bronchoalveolar Lavage:

The mineral fibers may be detected and quantified in the lavage fluid.

Pathology:

Gross:

Several firm, grayish-white or black nodules measuring from a few millimeters to some centimeters in maximum diameter are randomly distributed in both lungs.

Histology:

The nodules are composed of onionshaped, concentric bands of acellular collagen, and well demarcated from the adjacent lung parenchyma. Birefringent particles can be detected close to the boundary as well as dust-laden macrophages and scattered mononuclear inflamma tory cells; for details see under the heading silica.

Prognosis:

Fair; however, usually slowly progressive respiratory failure.

References:

search Pubmed for Cristobalite

Absher MP, Trombley L, Hemenway DR, Mickey RM, Leslie KO: Biphasic cellular and tissue response of rat lungs after eight-day aerosol exposure to the silicon dioxide cristobalite. Am J Pathol 134 (1989) 1243-1251
Hemenway DR, Absher MP, Trombley L, Vacek PM: Comparative clearance of quartz and cristobalite from the lung. Am Ind Hyg Assoc J 51 (1990) 363-369
Janko M, McCrae RE, O’Donnell JF, Austria RJ: Occupational exposure and analysis of micrcristalline cristobalite in mullite operations. Am Ind Hyg Assoc J 9 (1989) 460-465
Janssen YM, Marsh JP, Absher MP, Hemenway D, Vacek PM, Leslie KO, Borm PJ, Mossman BT: Expression of antioxidant enzymes in rat lungs after inhalation of asbestos or silica. J Biol Chem 267 (1992) 10625-10630
Lewis RJ: Carcinogenically active chemicals. Van Nostrand Reinhold, New York (1991)
Low BB, Leslie KO, Hemenway DR, Absher M, Adler KB, Giancola MS, Vacek PM: Alveolar type II cell response in rats exposed to aerosols of alphacristobalite. Am J Pathol 136 (1990) 923-931
Ostermann JW, Graves IA, Smith TJ, Hammond SK, Robbins JM: Work related decrement of pulmonary Lung Function in silicon carbide production workers. Br J Ind Med 10 (1989) 708-716
Sjostrand M, Absher PM, Hemenway DR, Trombley L, Baldor LC: Comparision of lung alveolar and tissue cells in silica-induced inflammation. Am Rev Respir Dis 143 (1991) 47-52