| contrasting density band that can be observed in the Y-cut quartz crystal by the Schlieren or similar optical method
Note 1 to entry: The cause of this contrast is that elements such as aluminium, sodium, lithium and iron are trapped in the quartz crystal when it is growing.
Note 2 to entry: Increased amounts of trapped impurities typically cause an increase in infrared absorption coefficient α at the specific absorption wave numbers.
Note 3 to entry: The growth band cannot be observed when α3 585 is less than 0,160 or α3 500 is less than 0,120.
Note 4 to entry: The growth band is used for the evaluation of synthetic quartz crystal for optical applications.
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