Umber

Abstract: The electrochemical response of different iron pigments attached to graphite–polyester composite electrodes is described. Characteristic differential pulse voltammetric profiles were obtained for green earth, iron oxide red, Mars black, ochre yellow, Sienna raw, umber raw and Van Dyke brown. Proton-assisted reductive dissolution processes occur at the three-phase boundary of the substrate electrode–attached solid–electrolyte solution system. Microsamples extracted from polychromed sculptures, canvas paintings, wall paintings, altarpieces and panel paintings from Spain, Ethiopia and Italy from the 12th to the 20th centuries were electrochemically identified in agreement with polarized light microscopy, SEM/EDX, XRD and FT-IR data.

Abstract: . Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today.

Abstract: On Leg 54 of the Deep Sea Drilling Project a transect of four drill-holes was placed across the Galapagos Mounds Hydrothermal Field. Basement basalts, pelagic sediments, and two types of hydrothermal sediments (Mn-oxides and Fe-rich green clays) were recovered. Stratigraphic examination of the cored sequence provides the following generalized sequence of a hydrothermal mound (from top to bottom): Mn-oxide cap, Fe-rich green clays (nontronite) layers intercalated with pelagic sediments, normal pelagic sediment, and basement basalts. The green clays have textures due to both replacement of previously existing sediment and open space filling. Thus, intercalation of the green clays with pelagic sediment may be indicative of a replacement-growth process during formation of the hydrothermal layers. The x-ray diffraction data, microscopic observations, and general chemistry reveal that the oxides are composed mainly of todorokite, birnessite, and amorphous compounds. Chemical analyses suggest that the oxides are nearly pure combinations of Mn, O, a d various amounts of H2O, with a conspicuous paucity of Fe and transition elements. The green clays are 10-12 A smectites (nontronite) that are chemically similar to glauconite. Mg probably substitutes for Fe in the clays, and K may occur as an adsorbed, interlayered cation. The smectites are also low in most transition elements. Oxide crusts from the uppermost cores in DSDP holes 424 and 424A contain Mn-oxides intimately mixed with the smectites. These phases were separated and were seen to correspond to chemical end members of a physical mixture in the sediments. A mixing line for hydrothermal material is suggested between these end members. Alteration of the underlying ferrobasalt is limited to "alteration rinds" around cracks, fractures, and flow surfaces. These rinds are formed by the precipitation of smectite, Fe-oxides, and minor amounts of calcite and pyrite is vesicles, microfractures, and primary porosity in the affected basalts. In general, the basalts are fresh and alteration is not pervasive. Umber deposits of the Cyprus ophiolite as described by Robertson (1975) are similar to the hydrothermal mounds under discussion in lack of pervasive basalt alteration and enrichment in Mn-oxides. It is proposed that Mn Deposits previously reported from ophiolite sequences may be analogous to the Mounds Mn-oxides.

Abstract: Pigments having the color of natural uncalcined umber contain more than 85% by weight of iron oxides, expressed as Fe2 O3, and less than 0.1% by weight of crystalline silica are obtained by mixing iron oxides of spinel structure and/or hematite structure with or without iron oxide yellow and said pigments are useful in coloring paints, lacquers and building materials.