St. Genevieve County

Iron, IIIF, octahedriteMost Common type of iron meteorite, composed mainly of taenite and kamacite and named for the octahedral (eight-sided) shape of the kamacite crystals. When sliced, polished and etched with an acid such as nitric acid, they display a characteristic Widmanstätten pattern. Spaces between larger kamacite and taenite plates are often Click on Term to Read More

Found during FallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If Click on Term to Read More of 1888
37° 58′ N., 90° 19′ W. A single spheroidal mass of 244 kg was found by Mr. Z. Murphy, a surveyor, ~1 mile west of the hamlet of Punjaub, which is near present-day Lawrenceton, Missouri. The St. Genevieve mass was bought by Ward several years later. Because of the long terrestrial age, several mm has been removed from the surface and terrestrial oxides are evident.

Group characteristics of the IIIF magmatic irons include very low-Co, high-Cr, and low-P contents. Other meteorites constituting group IIIF include Moonby, Clark County, Nelson County, and Oakley. In their paper ‘Chemical classication of iron meteorites–VIII’, Wasson and Scott (1975) determined that Oakley was the fifth member of a common grouping, which was thereby established as group IIIF. Since then the number of irons in this group has increased to nine.

In a study of W, Mo, and Ru isotopes in iron meteorites, Kruijer et al. (2017) recognized the existence of two distinct iron groups: those which accreted inside the orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around Click on Term to Read More of Jupiter where thermal processing occurred under reducingOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons,  while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More conditions (‘non-carbonaceous’), and those which accreted outside of its orbit where thermal processing occurred under oxidizingOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons,  while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More conditions (‘carbonaceous’). Interestingly, the pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category. Click on Term to Read More pallasites NWA 1911 and Zinder were determined to contain metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn Click on Term to Read More with a composition that is chemically identical to that of group IIIF irons (Boesenberg et al., 2017; Humayun et al., 2018). However, the IIIF irons formed in the carbonaceous region of the Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. beyond Jupiter, whereas the negative ε54Cr and δ26Mg* values of Zinder indicate that it formed in the non-carbonaceous region of the inner Solar SystemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with (Wimpenny et al., 2019). See the Appendix Part III for further details about these two regions.

The specimen of St. Genevieve shown above is a 55.4 g etched partial slice exhibiting a fine to medium Thomson (Widmanstätten) structure. The photo below shows the entire mass as photographed by Ward.