In fluorescent minerals, phosphorescence is an afterglow seen after the
ultraviolet light source is turned off. One of the more famous minerals
with long duration phosphorescence is calcite from the mercury mines in
Terlingua, Texas. The photo shown above shows the phosphorescence in response
to short wave ultraviolet. These mines are now closed and Terlingua
is a ghost town, but similar Terlingua-type calcites are available from
areas such as Challenger Cave in Nuevo Leon, Mexico.
Images © 2003 James O. Hamblen