Hematite in Quartz: “A Rose by Any Other Name”
Careful exploration of the micro-world can often reveal extraordinary crystal formations, even in relatively inexpensive, somewhat ordinary jewelry. The silver pendant shown in figure 1, measuring 31.50 × 17.00 × 10.00 mm, was purchased by author CF in 1996 from a Brazilian dealer at the Pueblo Show in Tucson, Arizona. It stood out among many others for its aesthetic swarm of crystal inclusions (later identified by their color and morphology as hematite), while their host was confirmed to be quartz using standard gemological techniques, including refractive index and optical testing. Several of the included crystals exhibited a complex habit known to mineral collectors as a “hematite rose”—an aggregate of crystal platelets arranged very much like the blooms of its botanical namesake. One of these inclusions was oriented in such a way that it lent itself to easy observation and photomicrography; this is not always the case with jewelry pieces whose construction may obscure the internal view or make lighting the inclusions tricky. A halogen light source with dual fiber-optic wands was used to successfully illuminate the rose from an oblique angle and to bounce light off the microscope plate in order to provide transmitted lighting (figure 2).
While quartz is a silicate, hematite is an iron oxide; both crystalize in the trigonal system. The surfaces of the fine, well-crystallized platelets of hematite exhibit triangular growth steps revealing this mineral’s underlying symmetry. These very thin plates reveal a deep red color in transmitted light. Quartz has a large thermal expansion coefficient, larger than that of hematite. Therefore, we would not expect cooling from the formation conditions to create a thin gap between the quartz and the hematite capable of producing thin-film interference colors, which are indeed absent here. Freely grown macro-specimens command hefty prices in the mineral-collecting world; however, an observant inclusionist may obtain one very frugally. This hematite crystal formation is as lovely as any rose and a fitting bloom for any gemologist’s micro-world garden.