Gem News International Gems & Gemology, Winter 2020, Vol. 56, No. 4

A New Phantom Quartz Imitation: Laser-Engraved Rock Crystal

Three-dimensional laser engraving in a natural quartz pendant.
Figure 1. The “phantom quartz” pendant was later confirmed to be natural quartz with three-dimensional laser engraving. Photo by Shu-Hong Lin.

Phantom quartz generally refers to a rock crystal with inclusions of prismatic or pyramidal growth zonation, which represents early crystal faces covered by minerals, such as clinochlore, clay minerals, limonite, or fuchsite. Recently, a new type of phantom quartz imitation has appeared in the market, most of which is sold in the form of beads, pendants, or crystal spheres. A package of these imi­tation phantom quartz products was sent to the Taiwan Union Lab of Gem Research (TULAB) for identification services (figure 1).

These samples submitted as phantom quartz had a powdery white growth zonation in the form of a hexagonal pyramid. The host crystal was confirmed to be natural quartz by infrared absorption spectroscopy. The samples had an abnormal appearance for phantom quartz, of which the internal growth zonation was composed of regular and oriented small cracks (figure 2). Similar inclusions are often found in crafts made of glass or synthetic quartz engraved with a laser. According to the client, one of these samples had fractures along the ridgeline of the apparent pseudo-hexagonal pyramid (figure 3), which were possibly self-propagated due to the internal stress from the oriented small cracks.

Laser impact created a regular network of small crack clusters.
Figure 2. The internal growth zonation was composed of a regular network of small crack clusters around a central black point, presumably due to laser impact. Photomicrograph by Yu-Ho Li; field of view 2.14 mm.
The imitation phantom crystal shows six fractures along ridgelines.
Figure 3. Left to right: A schematic diagram, a bottom view, and a top view of an imitation phantom crystal. The six fractures (red dashed lines) along the ridgeline of the pseudo-hexagonal pyramid in this imitation phantom quartz sphere were reportedly formed without any external force or heat treatment. The diameter of this sphere is 17.68 mm. Photos by Shu-Hong Lin.

In a true phantom, the axial direction of the host crystal is identical to that of the phantom crystal inside; however, the interference images through a polariscope revealed that the c-axis direction of these phantom quartz products was mostly inconsistent with what appeared to be their internal growth zonation (figure 4). In consideration of the morphological characteristics of inclusions as well as the interference images, these phantoms are imitations made of natural “rock crystal” with artificial growth zonation produced by laser engraving, irrespective of the crystallographic orientation of the host crystal.

The optic axis in relation to the “phantom” engraving.
Figure 4. Crossed polarizers revealed that the bull’s eye, indicating the optic axis, was nearly perpendicular to the axis of the engraved “phantom.” Photo by Shu-Hong Lin.

Although internal laser engraving can imitate the appearance of a phantom quartz inclusion, such products can be easily identified through a microscope and a polariscope. More controversially, the internal stress generated by the regular and oriented cracks seems to reduce the toughness of the host crystal; therefore, consumers should be aware of the risk of such imitations.

Shu-Hong Lin is director of Taiwan Union Lab of Gem Research in Taipei. Yu-Ho Li is a PhD candidate at the Institute of Earth Sciences, National Taiwan Ocean University in Keelung. Huei-Fen Chen is professor at the Institute of Earth Sciences and Center of Excellence for Oceans at National Taiwan Ocean University in Keelung.