This is probably due to the intense squeezing together of the atoms that must occur during their formation and the condensed structure that they are actually forced into forming. At surface temperatures and pressures, quartz is the most stable form of silicon dioxide, to no ones surprise. As the pressure increases the temperature at which quartz will lose stability also increases. Above 1300 degrees and at a pressure of approximately 35 kilobars, only beta quartz also known as high quartz is stable. Beta quartz is not the same as normal quartz, actually referred to as alpha quartz, low quartz or, as is mostly done here, just quartz.
Beta quartz has higher symmetry, is less dense and has a slightly lower specific gravity.
The conversion, from one solid substance to another solid substance, of quartz to beta quartz is quick, reversible and accompanied with a slight energy absorption. The conversion in fact is so easily accomplished that a crystal of quartz heated to beta quartz, cooled back down, heated again to beta quartz, etc and the crystal when all is done, will be the same as when it started. The reason that the conversion is so easily accomplished is that the difference between quartz and beta quartz is relatively slight. At the higher temperatures the atoms move away from each other just enough to allow the bonds to unkink or straighten and produce the higher symmetry. As the temperature is lowered, the atoms close in on each other and the bonds must kink in order to be stable and this lowers the symmetry back down again.