June 16, 2009
Researchers have reported the existence of a fivefold, natural quasicrystal, heretofore created only under controlled conditions. While ordinary crystals are limited to two-, three-, four-, and six-fold symmetry, quasicrystals, which are ordered rather than periodic, can display five-, seven-, and higher-fold symmetry axes.
Luca Bindi (Universita degli Studi di Firenze, in Florence); Paul J. Steinhardt and Nan Yao (both of Princeton University); and Peter J. Lu (Harvard University) discovered unique fivefold symmetry axes in samples of khatyrkite minerals, which are an alloy of aluminum, copper, and iron, in Russia's Koryak Mountains. Their finding seems to indicate that quasicrystals form and remain stable under geological conditions.
This purported natural, mathematically complex quasicrystal, which exhibits rotational symmetries not found in ordinary crystals, suggests that the definition of "mineral" may have to be revised and that the catalog of structures formed by nature expanded.
Insights into the formation and stability of quasicrystals not yet synthesized are sure to follow, thanks to the researchers' revelations in the article "Natural Quasicrystals," which appears in the June 5 Science.
"The study of natural quasicrystals may provide insights into the formation and stability of quasicrystals at temperatures and pressures not studied in the laboratory previously," the researchers conclude. "and perhaps an avenue for discovering new quasicrystals with compositions not yet synthesized."
Source: Science, June 5, 2009.