• DOI:10.1038/375544A0
• Corpus ID: 39954119

Native AI and Si formation

@article{Korzhinsky1995NativeAA,
  title={Native AI and Si formation},
  author={M. A. Korzhinsky and Sergey I. Tkachenko and Kirill I. Shmulovich and Genrikh S. Steinberg},
  journal={Nature},
  year={1995},
  volume={375},
  pages={544-544}
}

• M. Korzhinsky, S. I. Tkachenko, +1 author G. S. Steinberg
• Published 1 June 1995
• Geology
• Nature

SrRThe natural occurrence of elements such as aluminium and silicon in their native form is usually ascribed to either contamination or the presence of strongly reducing fluids 1 (for example, pure methane or hydrogen, although such fluids have never been found in nature). Here we describe the formation of crystals of native aluminium, silicon, titanium, iron and platinum inside the quartz tubes that we used to sample hot volcanic gas jets associated with Kudriavy volcano on lturup island in the Kuril arc. The gas emitted by the volcano consists mainly of water (93-97 mol%), C02 (1.3-4.4 mol%), H2S (::; 1.25 mol%) and S02 (::; 1 mol%), with small quantities of Hz, HCl and HF (ref. 2). It is important to note that the hydrogen concentration does not exceed 0.65 mol%, and the methane concentration is two orders of magnitude less. We determined the oxygen fugacity, f02, by two methods: thermodynamic calculations based on the CO/C02 and H2S/S02 of the gas, and direct measurement with an electrochemical cell• All measured and calculated values lie between the Ni-Ni02 and haematite-magnetite buffers, indicating an oxidizing environment. Fumarole sublimates were sampled using concentric quartz tubes inserted into cleaned volcanic conduits. The upper half of each tube protrudes from the conduit and is air cooled. The two fumaroles examined by this method had gas temperatures of 930 and 705 o C the corresponding temperature gradients in the sampling tubes were approximately 150 and 300 °C, respectively. The tubes were removed from the fumaroles after two months for laboratory examination. In the tube from the 930 o C fumarole, we identified precipitates of aegirine, fayalite, augite, rutile, Mg-calcite, apatite, magnetite, haematite, pyrite, pyrrohtite, molybdenite, sphalerite, galena, cubanite and complex sulphides. At the hot end of the tube, thin plates of platinum and iron were found. The Pt contained a small admixture of iron (::; 0.3%) whereas the iron was pure and homogeneous. The tube from the 705 o C fumarole was completely filled by sublimates having a total mass of 66 g and containing 78% sulphur, 12% halides (mainly NaCl and KCl) and 10% water-insoluble components. Halite and sylvite precipitated mainly in the hot part of the tube, whereas sulphur precipitates were found only in the upper part of the tube. Several minerals were identified, including SiOz, pyrite, plagioclase, K-feldspar, clinopyroxene, aegirine, augite and radite garnet, molybdenite, avogadrite, alpazolite and complex sulphides. Associated with the minerals, we found particles of native aluminium (96.11% pure by mass) and silicon (100% pure) and one plate of titanium (99.8% pure). The aluminium particles were found in the centres of Cl-rich spheres, growing outward to the rim as a sponge or honeycomb structure (a in the figure) and ranging in size from 0.1 to 3 mm. We could not determine the precise composition of the material in the sponge itself, but it appears to be enriched in Cl (as AlClx(OH)y)The outermost parts of the Al are partly replaced by KAl(S04)2*nH20. The native silicon occurs both as threadand diamond-shaped crystals within the Al, and as separate crystals (-0.1 mm in length) within Clrich spheres. The figure (b) shows one particle in which a large Si crystal is surrounded by Al-Si alloy with a texture typical of a eutectic.