Borosilicate minerals in granulite-facies rocks. My current National Science Foundation supported project is a study of boron-rich paragneisses in the Larsemann Hills based on samples collected on the Australian National Antarctic Research Expedition in 2003-2004 with Chris Carson (Geosciences Australia). The ferromagnesian borosilicates grandidierite and prismatine are major rock-forming minerals in these paragneisses (Figure 2). The Larsemann Hills is the type locality for boralsilite (Figure 3), a mineral related to sillimanite that I discovered in 1998. My former student Eva Wadoski completed a Master’s thesis on borosilicates in the pegmatites, with a focus on tourmaline, presented posters at several international meetings (Figure 4), and she published a paper in the Canadian Mineralogist (Wadoski et al. 2011). My current student, JohnRyan MacGregor, has analyzed tourmaline, prismatine and grandidierite for boron isotopes at the University of Edinburgh (Figure 5) as part of his Master’s thesis research. His objectives are to determine isotopic fractionation among these three borosilicates and to constrain possible protoliths of the boron-rich metasedimentary host rocks.
Phosphate minerals in granulite-facies metamorphic rocks and anatectic pods. The Larsemann Hills contain a remarkable variety of phosphate minerals for a metamorphic complex (9 species), including 3 of the 4 known polytypes of iron magnesium fluorphosphate wagnerite and 3 new species: stornesite-(Y), tassieite and chopinite. The last is a high-pressure polymorph of the meteoritic mineral farringtonite, Mg3(PO4)2, so my discovery of chopinite in Graves Nunatak 95209 (Figure 6), a primitive achondrite , raises questions about the evolution of the asteroid from which this meteorite originated.
Evolution of the minerals of beryllium and boron. Robert Hazen invited me to collaborate on a series of papers on the mineral evolution of specific elements as follow up of his 2008 paper “Mineral Evolution” published in American Mineralogist, vol. 93, pp.1693-1720. I started with the 106 minerals of beryllium, the oldest of which formed in the Mesoarchean. I have studied three Be minerals, khmaralite, magnesiotaaffeite-6N’3S (formerly musgravite) and surinamite from the earliest Paleoproterozoic (2485 Ma) granulite-facies anatectic veins in the Napier Complex, Antarctica (Figure 7). Of particular interest is the role of borates in the “RNA World” thought to have been an important link between purely prebiotic (>3700 Ma) chemistry and modern DNA/protein biochemistry. However, it remains an open question whether borate minerals were around so early in Earth history (Grew et al. 2011).
Menzerite-(Y), new species of garnet, and the garnet nomenclature. Jeff Marsh, who was awarded a Ph.D. in 2010, discovered an yttrium rich mineral in a pyroxene granulite on Bonnet Island (Figure 8 ) in the interior Parry Sound domain, Central Gneiss Belt, Grenville Orogenic Province, Canada, his thesis area. Crystallographic studies show the mineral is a garnet (Figure 9), and the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association has approved our proposal for the new mineral, menzerite-(Y), which was described in the Canadian Mineralogist (Grew et al. 2010). I am currently chairing the Garnet Subcommittee, which is preparing a recommended nomenclature for the Commission to vote on.
Figure 1. Ed Grew on the outcrop, Larsemann Hills, Antarctica
Figure 2. Photomicrograph of prismatine (high relief, pale) around grandidierite (blue) in plagioclase. Brown grains are tourmaline. Plain light. Larsemann Hills.
Figure 3. Photomicrograph of twinned boralsilite prisms. Crossed nicols. Larsemann Hills, Antarctica.
Figure 4. From left: Milan Novák, Eva Wadoski, Ed Grew and Jan Cempírek at the Granulites & Granulites 2009 conference in the Hrubá Skála chateau, Czech Republic, July 14, 2009
Figure 5. JohnRyan MacGregor analyzing boron isotopes on the ion microprobe at the University of Edinburgh, Scotland in 2011.
Figure 6. Meteorite from Graves Nunatak, Antarctica, containing chopinite
Figure 7. Photomicrographs in plane light of Paleoproterozoic beryllium minerals. Scale applies to both photographs. (a) Part of corona around deeply embayed sapphirine-khmaralite (Spr) showing inner sillimanite (Sil) zone and part of outer garnet (Grt) zone with surinamite (Sur). (b) Ilmenite-hematite intergrowth (opaque) with tabular musgravite (Mgr), minor surinamite (Sur) and relict sapphirine-khmaralite (Spr) (from Grew et al., 2000).
Figure 8. Jeff Marsh pointing to the layer containing an yttrium garnet, possibly a new mineral species, on Bonnet Island, Georgian Bay, Ontario. June 10, 2009
Figure 9. Photomicrograph of two garnets: euhedral almandine crystals cored by dark-brown menzerite-(Y). Matrix is plagioclase. Plane polarized light.