Aqua Aura Quartz

This material is produced, not found in nature. Natural quartz crystals or beads are placed in a vacuum chamber and gold is evaporated so that its atoms deposit as a film on the quartz surface; the same technique is used to coat samples for electron microscopy. The thin gold film looks blue-green in transmitted light, which gives the blue color, while the iridescent colors depend on the film thickness. Coated quartz of this kind was first reported in the gem trade in 1988.

Gemological tests show ordinary quartz properties (refractive index about 1.54–1.55, specific gravity about 2.66, doubly refractive, inert to ultraviolet light). Under magnification the coating can be seen to vary in thickness, with color concentrated near crystal edges, little or no coating in surface pits, and small uncoated or worn areas showing colorless quartz. Laboratory analysis (EDXRF) identified the coating as gold.

The color exists only in the surface film. In GIA testing of one crystal in 1989 the gold coating resisted acetone, heat and a hardness-6 point but was scratched by a hardness-7 point; GIA notes that thin-film coatings in general can scratch, especially along edges and facet junctions. Keep coated pieces away from hard or abrasive objects, avoid abrasive cleaners, and store them wrapped in soft material in a dry place.

GIA researchers first examined this coated quartz in the fall of 1988, when crystals and clusters from Bob Jackson Minerals of Renton, Washington, were being sold under the trade name "Aqua Aura" with promotional text describing them as natural quartz crystals coated with pure gold. Their 1989 report in The Journal of Gemmology confirmed that the coating is gold and described it as a spin-off of thin-film gold-coating technology.