Few gemstones are prized for their beautiful inclusions. Consider the overwhelming popularity of diamond, which is most valuable when it is inclusion-free. Internal growth features in most gemstones are typically considered by jewelers and consumers alike to be flaws, and their presence reduces the gem’s value.
But for the jeweler/gemologist, there is absolutely nothing like the excitement generated in seeing a three-phase inclusion with a perfect halite crystal encased alongside a gas bubble in a liquid cavity, establishing the origin of a Colombian emerald … or finding a deliberately positioned central horsetail of byssolite fibers in a Russian demantoid … or better still, a swirling fingerprint inclusion comprising hundreds of aligned octahedral crystals in a Burmese flame spinel. But these rare internal beauty marks are appreciated only by those who examine gems under magnification.
There are, however, a small number of gems appreciated by both jeweler/gemologists and consumers for their visible inclusions. Other minerals, trapped inside a growing gem crystal, often can enhance the gem’s outward beauty. Rutile needles encased in rock crystal quartz is a great example of this natural art.
Occurrence. Found mainly in Brazil, rutilated quartz takes its name from the rutile needle-like inclusions captured by the rock crystal quartz host. Rock crystal is an especially good gem material to show off internal features, as it is by definition transparent and colorless. Rock crystal quartz is, after all, the material used for the famed “crystal ball.”
It’s not uncommon to find random rutile needles within rock crystal. But finding these golden color fibers in pleasing patterns is much more difficult. The phenomenon of crystal growth shows itself quite dramatically in the creation of rutilated quartz, especially when the growth of the rutile needles is arranged in a six-ray star.
To create this mineral combination of rutile in quartz, a hematite crystal is necessary. The rutile grows on the surface of the hematite in what is called an epitaxial relationship. “Epitaxy” occurs when the growth of one crystal (in this instance, the rutile) follows the growth direction of whatever it is growing on (in this case, hematite). The hexagonal symmetry of the hematite controls the orientation of the rutile, forming the six-leg star.
All of this wonderful crystallographic activity happens inside a quartz cave, called a pegmatite. Pegmatites occur when volcanic intrusions of hot magma, or hydrothermal solutions, cool and allow gem minerals to crystallize. You can find any number of minerals—and, if we’re lucky, gemstones—in pegmatites. A typical pegmatite can be a yard wide by half a mile long, coursing through other minerals and rocks. Besides rock crystal, you can also find aquamarine, tourmaline, kunzite, and roughly 20 or 30 other minerals in quartz pegmatites. It is within these pegmatites that the rutile needles, grown first, are encased in the growth of rock crystal.
Variations. The variations of rutilated quartz occur both in nature and at the bench of the gem artist. Nature dictates the direction, size, and color of the rutile needles; the gem artist determines how the needles will be viewed in a finished piece. Thin needles, broad flat needles, omni-directional needles, needles that are scattered chaotically, and many other variations and orientations can inspire the gem artist to create cat’s-eyes, stars, and a host of other gemstone works of art.
Qualities. The more crystal-clear the rock crystal, and the more brightly golden-color the rutile needles, the higher the quality of rutilated quartz. Included rock crystal with just one or two rutile needles will not be considered fine quality. The rutile must be noticeable and must form some type of artistic design. To give some sense of the gem’s rarity, experts have said that, of all the rutilated quartz that has been uncovered, there are so far only a few dozen really nice, clean, and beautifully crystallized rutile-star quartzes.
Value. Most people tend to prefer symmetry as opposed to asymmetry. Therefore, the more uniform the needles and the more uniform the pattern or direction of growth, the higher the value. Value also increases with color and visibility. Because the complete six-ray stars are the hardest to find, they will be the most valuable. Nice-quality cat’s-eyes are only slightly easier to find and also are considered quite valuable.
Pricing. Six-ray stars top the price chart. The round star cabochon in the photo has an estimated value of $1,000. A larger piece, about the size of an adult fist, was recently priced at approximately $9,000. For large faceted pieces with unusual needle placement, like the shield cut shown in the photo, prices can settle near $400-$500.
Care and cleaning. Because the quartz material has a hardness of 7, be sure to wash off any dust before you wipe the quartz with a cloth. The dust, which also has a hardness of 7, will scratch the polished surface, and while you may never see the very fine scratches, they will eventually dull the gem’s appearance.
Bench settings and precautions. As with other unusual gems, these rare natural beauties should be unmounted before attempting any manufacturing or repair procedures. Always protect the gem from possible scratches from dust that can accumulate in almost any shop area.
Some native-cut cat’s-eyes may be cut as a double cabochon, which makes it extremely difficult to mount. Repolishing a flat bottom to the gem may remove the rutile fibers needed to create the best cat’s-eye.
Special thanks to Tony Kampf, director of mineralogy, Natural History Museum, Los Angeles, and Bill Heher, Rare Earth Mining, Trumbull, Conn.