Smoky quartz crystal with clear top

A smoky quartz crystal from Brazil with a clear tip. The optical zoning from a dark base to a transparent tip is directly readable as the growth history of the crystal.

Smoky quartz is a variety of quartz that has been darkened by natural radiation. Aluminum substitutions in the crystal lattice are stimulated by radioactive background radiation to form color centers. The intensity of the discoloration documents the radiation dose and growth time.

The clear tip forms when the radiation source diminishes during the growth phase or when crystal growth ceases. The result is an optical stratigraphy that combines a dark base and a clear cap in a single crystal.

Such smoky quartz tips from Brazilian pegmatites are classic collector's items. The clarity zoning increases the material value beyond standard smoky quartz.