Editing Crystal oscillator (section)

==== Types ====
Two types of quartz crystals exist: left-handed and right-handed. The two differ in their [[optical rotation]] but they are identical in other physical properties. Both left and right-handed crystals can be used for oscillators, if the cut angle is correct. In manufacture, right-handed quartz is generally used.<ref name=terms>[http://www.ndk.com/catalog/AN-SQC_GG_e.pdf Synthetic Quartz Crystal] Terms and Definitions</ref> The SiO<sub>4</sub> tetrahedrons form parallel helices; the direction of twist of the helix determines the left- or right-hand orientation. The helixes are aligned along the c-axis and merged, sharing atoms. The mass of the helixes forms a mesh of small and large channels parallel to the c-axis. The large ones are large enough to allow some mobility of smaller ions and molecules through the crystal.<ref>[http://www.quartzpage.de/gen_struct.html The Quartz Page: Quartz Structure]. Quartzpage.de (2010-10-23). Retrieved on 2012-06-21.</ref>

Quartz exists in several phases. At 573&nbsp;°C at 1 atmosphere (and at higher temperatures and higher pressures) the α-quartz undergoes [[quartz inversion]], transforms reversibly to β-quartz. The reverse process however is not entirely homogeneous and [[crystal twinning]] occurs. Care must be taken during manufacturing and processing to avoid phase transformation. Other phases, e.g. the higher-temperature phases [[tridymite]] and [[cristobalite]], are not significant for oscillators. All quartz oscillator crystals are the α-quartz type.