Updated November 28, 2007

Amorphous silicon dioxide (SiO₂) is basically a form of glass. Also called silica or silox, semiconductor fabs use silicon dioxide as an insulator (it's the insulator in the SOI acronym silicon on insulator). SiO2 is a great electrical insulator, but a very poor thermal conductor. It has a very low coefficient of expansion, like Pyrex glass. Low expansion coefficient is actually why Pyrex doesn't shatter when you pour hot liquids into it! The low dielectric constant and low loss tangent make SiO₂ a very low-loss material for microwaves. Silicon dioxide-filled semi-rigid coax cables can withstand temperatures that would cause PTFE-filled cables to catch on fire!

Fused silica and fused quartz are forms of silicon dioxide.

Sources for this data include Wikipedia.

Formula or Composition:	SiO2
Dielectric Constant ():	3.9
Dissipation Factor (a.k.a. loss tangent, or tan):	0.001
Temperature Coefficient of :	ppm/°C
Bulk Resistivity:	1E10-cm
Temperature Coefficient of Resistivity (TCR):	ppm/°C
Mass Density:	2.203 gr/cc
Specific Heat:	0.703 J/g/°C
Thermal Conductivity (k):	1.3 W/m°C
Temperature Coefficient of Expansion (TCE):	0.55 ppm/°C
Melting Point, °C:	1650 °C 3002 °F