February 2, 2010, Chantilly, Virginia:

Nemchin et al. in “Distribution of rare earth elements in lunar zircon” aimed to (1) determine limits of variation of REE concentrations in lunar zircon of different origin, particularly those formed from magmas of different composition and use this information as a petrogenetic indicator, and (2) test existing zircon-melt distribution coefficients for REE (^zircon/meltD_REE) to enable calculation of REE content of melts coexisting with the zircon. Understanding REE distribution in zircon is particularly relevant to lunar rocks where zircon grains occur as separate mineral fragments and as components in small igneous clasts of uncertain affinity. The REE signatures of these zircon grains may provide a basis for correlation and petrologic interpretation, which can be used to understand the age data. Additional insights into processes that control distribution of REE in zircon can be gained by studying grains found in lunar rocks. The advantage of such studies is that the lunar zircon grains are relatively simple. However, few REE analyses of lunar zircon grains have been reported. In this paper, Nemchin et al. present REE analyses of 15 zircon grains extracted from breccia sample 14321, discuss their compositional variations, and compare the observed REE patterns to some terrestrial zircon grains, including the oldest grains from the Jack Hills metasedimentary belt. In addition, they report 11 analyses of REE in a complex zircon, consisting of broken fragments surrounded by a glassy zircon matrix, found within an anorthosite clast in breccia thin section 73235,82. These results provide information on the effect of large impacts on the behavior of REE in zircon.

For the first time in biominerals, Vielzeuf et al. in “Multilevel modular mesocrystalline organization in red coral” observe a long-range crystallographic order and a hierarchical organization consisting of different levels of similarly (but not identically) oriented modules. Modules assemble into larger modules and consist themselves of smaller modules. They demonstrate that red coral acts as an astute crystallographer, assembling its skeleton as a delicate arrangement of a hierarchy of crystals with well-defined orientations relative to their near- and far-field neighbors. Modularity has implications on the debated issue concerning the design of complex shapes in biominerals with elementary crystalline bricks. The concepts developed in this article may prove useful to develop new strategies to design complex-shaped three-dimensional crystalline synthetic materials, which is a present-day challenge in materials science.

Enjoy and learn from the many other articles in this packed issue of Am Min!

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