George W. Robinson

Naturally occurring graphite cones

Abstract Carbon, boron nitride, and other materials that form nanotubes are also able to form conical shapes. Even though the potential applications of cone arrays as electron emitters and other devices are very promising, understanding of their structure and formation mechanisms is still very limited compared to nanotubes and other carbon structures. Moreover, the cones have only been synthesized in a mixture with other shapes, but never as continuous arrays. It appears, however, that we can learn from nature how to produce large carbon cone arrays. We here report the first-known natural occurrence of large arrays of conical graphite crystals. These occur on the surfaces of millimeter-sized polycrystalline spheroidal aggregates of graphite. Cone heights range from less then a micron to 40 μm, which is larger than any other carbon cones reported in the literature. They are also observed to dominate sample surfaces. The surface topography of the cones and petrologic relations of the samples suggest that the cones formed from a metamorphic fluid. Unlike most laboratory produced cones, the natural cones have a wide distribution of apex angles, which supports a disclination model for cone-helix structures.

Paleokarst in the Lower Ordovician Beekmantown Group, Ottawa Embayment: Structural control inboard of the Appalachian orogen

Two paleokarsts, different in age, character, and origin, occur in dolostones of the Lower Ordovician Beekmantown Group of eastern Ontario, well within the interior of the Laurentian paleoplatform. Surficial to shallow subsurface ( p CO 2 and H 2 S concentrations arising from mixing of continentally derived pore waters with brines derived from dissolution of Beekmantown evaporites. Compared to the region9s geologic history, a pre–late Paleozoic age for formation of the regional paleokarst and mineralization is likely. The two platform-interior paleokarsts demonstrate unexpected links between tectonism, changes in paleohydrological patterns, and porosity development well inboard of the Appalachian orogen.

The geochemical record of hydrothermal mineralization and tectonism inboard of the Appalachian Orogen: the Ottawa Embayment

Abstract The history of mineralization of the Ottawa Embayment includes migration of basin brines within the confines of an Early Paleozoic basin, and cross-stratal fracture flow linked to structural reactivation of an underlying Neoproterozoic failed-rift system. Paleoporosity consists of paleokarst (PAL) in Lower Ordovician dolostone (Beekmantown Group), and fractures (now veins) that cross-cut both Lower Paleozoic (PL) and Precambrian (PC) strata. A series of contrasting mineral assemblages, which define changing fluid compositions, fill paleokarst cavities and rare interconnected paleofractures (now veins). First, there is an early-PAL succession of quartz, saddle dolomite, then calcite, with accessory hydrocarbon as well as sulphide and sulphate minerals. The quartz defines migration of saline (>20 wt.%) silica brines and hydrocarbon that spans a temperature increase (defined by fluid inclusions) from δ 13 C of the dolomite identifies strong sedimentary rock–water interaction, but a depleted 13 C composition (∼−14‰) for the calcite illustrates that, with cooling, paleokarst cavities were sites of bacterially mediated sulphate reduction. Remaining paleokarst porosity is filled with a late-PAL mineral assemblage that contains low-temperature (mostly

Spherical and triskelial graphite from Gooderham, Ontario, Canada

THE SIXTEENTH TECHNICAL SESSION OF THE Rochester Mineralogical Symposium was held on I b April 1999. Seventeen abstracts were accepted, and twelve were presented during the platform session moderated by Dr. Carl A. Francis. Submitted abstracts were reviewed by a committee consisting of Dr. Steven C. Chamberlain, Syracuse University; Dr. Carl A. Francis, Harvard University; Dr. Robert I. Gait, Royal Ontario Museum; Dr. William Kelly, New York State Geological Survey; Dr. Robert J. King, Tewksbury, Great Britain; and Dr. George W. Robinson, Michigan Technological University. The accepted abstracts follow.

Greenockite and Associated Uranium-Vanadium, Minerals from the Huron River Uranium Prospect Baraga County, Michigan

4A. E. Seaman Mineral Museum and Department of Physics Michigan Technological University 1400 Townsend Drive Houghton, Michigan 49931 jaszczak@mtu.edu T he Huron River uranium prospect is one of several baseand preciousmetal explorations in the vicinity of the Huron River drainage system and the western flanks of the adjacent Huron Mountains (Kalliokoski and Lynott 1987). Although there are no true mines, historic or modern, in this part of Baraga County, the area is intriguing in that it lies nearly equidistant between two world-class mining districts: the famous Michigan native copper district to the northwest, and the Marquette Range iron (and gold) mining district to the southeast. Classical geological features such as a well-exposed Precambrian unconformity at the Big Eric’s Crossing of the Huron River (also a popular camping site) draw geologists and students to the region each year. Figure 1. Contact between mineralized brecciated quartzite and Michigamme Slate at the Huron River uranium prospect; Mark Elder photo.

The Graphites of New York: Scientific and Aesthetic Surprises

In an effort to improve his health, Benjamin Silliman (1779–1864) traveled in the latter part of May and early June 1821 with Samuel F. B. Morse to areas along the upper Hudson River and Lakes Champlain and George. In his notes made during this trip Silliman (1822), who was a professor of chemistry, mineralogy, and other subjects at Yale College and also founder and editor of the American Journal of Science*, made the following observation regarding graphite, which he referred to by its then common but now obsolete synonym, plumbago: “This mineral, of singular beauty, occurs near Ticonderoga, both massive and disseminated, in brilliant plates, in a large grained crystallized limestone.” With an air of regret, Silliman noted that he was unable to visit graphite occurrences at Ticonderoga and at Roger’s Rock “from want of time and want of health.” What “singular beauty” does graphite from the state of New York

Pink Petoskey Stones from Northern Michigan

Petoskey stones have been collected in northern Michigan for more than a century and are familiar to many collectors. Composed of calcite, the Petoskey stone is actually a Devonian-age fossil coral with a distinctive hexagonal pattern consisting of small six-sided chambers in which corals once lived approximately 350 million years ago when the Michigan Basin was under a sea. Petoskey stones comprise several species of the genus Hexagonaria; although they occur in slightly different sizes and shapes, all show hexagonal GEORGE W. ROBINSON A. E. Seaman Mineral Museum Michigan Technological University 1404 East Sharon Avenue Houghton, Michigan 49931 robinson@mtu.edu

Minerals of the Beekmantown Group, Southeastern Ontario, Southern Quebec, and Northwestern New York

Overshadowed by such famous localities as Mont Saint-Hilaire and the Francon quarry in southern Quebec, or classics such as Pierrepont, DeKalb, Rossie, and Antwerp in upstate New York, it is little...