Chemical formula: SiO2
Modifications: Several silica modifications are known. The following phases are stable at ordinary pressure: quartz - high quartz - tridymite - cristobalite - melt.
Melting point (high cristobalite): 1723oC
Stability range (high cristobalite): 1470-1723oC
Transformation point (high-low cristobalite): 180-270oC
Density: 2.23 (high), 2.32-2.38 (low) g/cm3
Microhardnes: cca 1600 kp/mm2 (low)
Hardness (Moh's): 6-7
Luminescence: Cristobalite often shows a light-blue fluorescence in EPMA.
Colour in air, bright field reflection: Milk white (beta-cristobalite)
Colour, polarized reflection: No data
Shape: No data
Crystal system: Tetragonal, pseudocubic
Cell dimensions: a=4.9709 A, c=6.9278 A
PDF number: 00-001-0424
ICSD number: 024587
Note: In non-metallic steel inclusions cristobalite often crystalizes as dendrites in a glassy ot crystallized matrix of various metal silicates. The polished microsections of these dendrites often aooear as rosettes. Cristobalite also occurs as a scale around the inclusions and lining the inside of the blowholes which are often visible in silicate inclusions.

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