In mineralogy there are geometrical terms to describe the various crystal systems, such as cubic, tetragonal, monoclinic and triclinic. But there is another set of terms that mineralogists use to describe the typical appearance, or habit of crystals. They include various shape and size terms such as bladed, botryoidal (globular), columnar, and sphenoid (wedge-shaped).
Many of these are technical terms of mineralogy, but one of them has become important in the world of gems and jewelry. The term drusy, used to refer to encrustations or clusters of minute crystals, has become familiar to many jewelry designers and consumers. Drusy incorporated into jewelry provides a unique look like the sparkling of sugar or snow.
You will sometimes see the term spelled druzy or druse or drusies, but all these terms refer to the same thing -- tiny crystals that form within or on the surface of other minerals. By far the most commonly found drusy is quartz (agate or chalcedony), but many other species can exist in this form. Other types of drusy include uvarovite garnet, rainbow pyrite, rainbow hematite, chrysocolla, calcite, dolomite, sphalerite, demantoid garnet, melanite garnet, azurite, dioptase, turquoise and vanadinite.
Rainbow Pyrite Drusy
In drusy gemstones, quality is determined not just by color, weight and clarity, but also by the size and evenness of crystal coverage. The evenness with which the matrix is covered is an important value point. Good drusies are relatively rare, especially in non-quartz species.
Drusy can be quite delicate compared to typical faceted and cabochon gemstones. The toughness of each drusy piece depends on the nature of the crystals themselves and the matrix in which they are embedded. For example, quartz drusy is relatively durable while calcite drusy is quite fragile. Any drusy is probably more fragile than a single crystal of the same gem variety, as in addition to the usual worry of scratching or breaking, there is always a risk of detachment of the tiny crystals from the matrix.