Geochemistry of agates: a trace element and stable isotope study

Quantitative mapping of trace elements in agate using LA-ICP-MS

“…The compositional variation and rhythmic banding of Al in the samples are typical for silica precipitation at low temperatures below 300°C (Rusk et al 2011). Agates commonly contain considerable amounts of mineral and fluid inclusions possibly responsible for their different coloration (Götze et al 2001). The quantitative Fe and Mn elemental maps and microscopic images of the colorful agate sample clearly showed spot-shaped numeral mineral inclusions definitely changing from Fe oxide/hydroxide in the inner half to Mn-bearing hollandite in the outer half (Fig.…”

“…6b-d). Such fluctuations of trace element concentrations might be associated with abundance of microcrystalline quartz (Götze et al 2001). The partitioning of trace elements into chalcedony stronger than that into microcrystalline quartz might result in the concentration of transition metals at bluish bands.…”

“…Agate is an aggregate of various forms of microcrystalline silica, mainly chalcedony, and is generally formed by chemical precipitation in rock cavities (Götze et al 2001). Chalcedony occurs commonly in a semitransparent or translucent state, with waxy luster, and varies widely in color, in contrast to colorless, transparent microcrystalline quartz (Polk 2012).…”

“…Chalcedony occurs commonly in a semitransparent or translucent state, with waxy luster, and varies widely in color, in contrast to colorless, transparent microcrystalline quartz (Polk 2012). Transition metals incorporated during the precipitation color agates (Götze et al 2001;Möckel et al 2009). The species and concentration of transition metals in agate are commonly reflected by its rhythmic color banding (Heaney and Davis 1995).…”

Mineral chemistry of some agates from Gurasada (Mures Valley, Romania)

“…vesicles. The geochemical study of Götze et al (2001) demonstrated that the formation of agate can be a complex, multi-steps process which takes place during the formation and alteration of the parental volcanic rock. The trace element and the isotope data lead to the conclusion that the SiO 2 necessary for the agate formation is mobilized during the alteration of the volcanics by own hydrothermal solutions (auto-metasomatosis).…”