Drusy; this is a micro crystalline incrustation of crystals that has a similar look to that of fine Pave Diamonds, but occurs naturally when water forms on a rock and then evaporates. When tiny crystals of quartz form on agate this can be called drusy- agate (Agate: a form of chalcedony with striped or clouded colorings).
Most often druzy encrustations are found in the center of quartz (chalcedony, amethyst, citrine or agate) geodes but they are also found on the surface of non-quartz minerals such as Chrysacola, Cobalto or Pink Calcite, Uvarovite Green Garnet, Black Garnet and Rainbow Hematite or Rainbow Pyrite as well as other minerals.
Some druzies such as Uvarovite Green Garnet and Pink Cobalto Calcite have naturally occurring vibrant coors. Most druzies which occur in the form of quartz have more muted colors such as white, grey, tan, brown and cream. Too create more variety in colors, quartz druzy is often dyed black or other vivid colors such as pink, purple, red, green, yellow and blue. They are also vapor coated with titanium, cobalt, gold or other metals or mixes of metals to create various iridescent finishes.