The object of the present work is to investigate the characteristics of piezo-electric resonantors which are cut from the natural coloured quartz, and compare the results with those obtained from those plates cut from the ordinary clear quartz in order to see if coloured quartz might be used as piezo-electric material in practice. In this work four points were stressed, they are: (1) the frequency constants of piezo-electric oscillation, (2) its stability, (3) its selectivity and activity and (4) its frequency-temperature coefficient curves. Further more a comparison of the characteristics of oscillations before and after the heat-treatment of the material was made. By the results of these experiments it concludes that the natural coloured quartz plates can be excited into piezo-electric oscillation and serve as piezo-electric resonantors. The frequency constant of a Y-cut plate from coloured quartz is about 2% lower than that of same type cut plate from clear quartz, while the frequency constants of the X-cut plate and the AT-cut plate from the coloured and clear quartz are practically the same. The heat-treatment to the three types cut plates of both kinds of quartz has a definite influence on their frequency. This effect is more pronounced to the coloured quartz plates. Likewise, heat-treatment improves, from the point-view of statistics, the selectivity and activity of oscillation of both kinds of quartz. Finally, the values of some coefficients of stiffness of the coloured and clear quartz were discussed.
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