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An investigation has been carried out aimed at developing a process for the growth of large crystals of synthetic quartz using silica-rich rocks native to the United Kingdom as the raw material. As a result of this work the effect of impurities on the habit and quality of the crystals has been determined. The role of aluminium as a key impurity has been proved and the darkening produced by X-irradiation has been used to study the distribution of impurities in the synthetic quartz. Recent work has thrown further light on the manner in which aluminium, possibly associated with another element, is incorporated in the quartz structure.

Processes for the growth of large crystals of synthetic quartz of piezo-electric quality are now well-established. They all involve the recrystallization of quartz from solution under conditions of elevated temperature and pressure. Two recent developments, which could have profound effect in the future, are described, namely the use of impure nutrients as the source of silica, and the development of a technique for the growth of crystals of the highest possible quality for use in frequency standards and other high-stability applications.

A process for the growing of quartz crystals artificially is briefly described. This so-called synthetic quartz, which is being grown reproducibly as well-formed crystals weighing about 135 grammes, possesses electrical and mechanical properties which closely follow those of the natural Brazilian quartz commonly used for piezo-electric purposes. The high overall quality of synthetic quartz, its freedom from twinning and other faults and its regular shape and size make it a convenient material to handle with the minimum of wastage. Measurements have been carried out to compare the properties of oscillator crystals cut from natural and synthetic quartz. The behaviour of the AT- and BT-cuts has been investigated thoroughly, while some results have also been obtained on units of the CT-, DT-and 5° X-cuts. Most of the parameters measured show no appreciable difference between the values for natural and synthetic quartz. Two notable exceptions are a small difference in the frequency/temperature characteristics of AT-cut units, whether operated at fundamental or at overtone frequencies, and an apparently reduced activity of face-shearmode units of the CT-and DT-cuts from the synthetic material. The significance of these results is discussed, together with the possibility of more accurate measurements to compare the intrinsic mechanical losses in natural and synthetic quartz.