Hi Ralph, First of all, the word is spelled “drusy” and derives from
the more technically correct term “druse.” It refers to a stone
whose surface is covered with small crystals, such as the quartz
crystals that line the interior of many geodes. In fact many drusy
stones are cut from geodes though not all drusies are quartz. Just a
couple of examples are the emerald green colored uvarovite garnet
crystals on black matrix and the hot pink cobalto calcite (or, more
properly, cobalto dolomite) crystals on brownish matrix.
Perhaps the most popular drusy stones for jewelry are the various
black drusies: natural black psilomelane with a quartz crystal
surface, black drusy agate (quartz crystals over dyed agate) and
black garnet drusy, among others. Also popular of late are the
various dyed or coated drusies such as the newly dubbed Tucsonite
(platinum coated drusy agate). The varieties and colors pretty much
span the spectrum.