Scientists Verify World’s Largest Single Crystal of Gold

From Laboratory Equipment:

When geologist John Rakovan needed better tools to investigate whether a dazzling 217.78 gram piece of gold was in fact the world’s largest single-crystal specimen — a distinguishing factor that would not only drastically increase its market value but also provide a unique research opportunity — he traveled to Los Alamos National Laboratory’s Lujan Neutron Scattering Center to peer deep inside the mineral using neutron diffractometry. Neutrons, different from other probes such as X-rays and electrons, are able to penetrate many centimeters deep into most materials.
Neutron diffraction data collected on the single-crystal diffraction (SCD) instrument at the Lujan Center, from the Venezuelan gold sample, indicate that the sample is a single crystal. Image: Los Alamos National Laboratory

“The structure or atomic arrangement of gold crystals of this size has never been studied before, and we have a unique opportunity to do so,” the Miami Univ. professor says.

Revealing the inner structure of a crystal without destroying the sample — imperative, as this one is worth an estimated $1.5 million — would allow Rakovan and Lujan Center collaborators to prove that this exquisite nugget, which seemed almost too perfect and too big to be real, was a single crystal and hence a creation of nature. Its owner, who lives in the U.S., provided the samples to Rakovan to assess the crystallinity of four specimens, all of which had been found decades ago in Venezuela.

During the past Lujan Center user run cycle, Heinz Nakotte, New Mexico State Univ. professor and lead scientist for the single-crystal diffraction (SCD) instrument, and Sven Vogel, instrument scientist for the high-pressure/preferred orientation (HIPPO) instrument, helped Rakovan probe the stunning pieces at Los Alamos. The authors are preparing a scientific report.

Three of the four samples turned out to be single-crystal pieces of gold, rather than the commonplace multiple-crystal type. Of particular interest was a golf-ball-shaped nugget that at one time was believed to be the world’s largest trapezohedral gold crystal. In 2006 the crystal had been rejected at auction over questions of authenticity, and indeed, the Los Alamos instruments confirmed that it was not a world-record trapezohedral crystal.....MORE