Quartz Crystals and Their Colors

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Abstract
The many colors found in quartz crystals are always due to the presence of impurity atoms, whose concentrations rarely exceed 0.1 wt.%. The impurity atoms occupy either silicon sites in the lattice or interstitial sites in the channels parallel to the c axis of the quartz structure; very fine precipitations of foreign phases are sometimes also observed, though this is less common. In addition to intrinsic colors of transition metal ions, one also finds color centers produced by ionizing radiation. Regular distributions of impurity atoms and colors may develop in the crystals as a result of some factor connected with its growth. Most of the natural quartz colors, as well as others that do not occur in nature, have been produced in synthetic quartzes.