Quartz



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: 1710oC
Stability range: <573 (low), 573-870oC
Transformation temperature low-high: 573oC
Density: 2.651 (low), 2.518 (high at 600oC) g/cm3
Microhardnes: cca 1600 kp/mm2 (low)
Hardness (Moh's): 7
Luminescence: No data
Crystal system: Hexagonal
Cell dimensions: a=4.903, c=5.393 A
PDF number: 00-001-0649
ICSD number: 079634
Note: Low quartz in steel inclusions has been observed as dark grains which form more or less regular plates in polished sections.




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