Fulgurite morphology: a classification scheme and clues to formation
Fulgurite morphology: a classification scheme and clues to formation
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DOI：
10.1007/s00410-012-0753-5
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发表时间：
2012-09-01
影响因子：
3.5
通讯作者：
Pasek, Virginia
中科院分区：
文献类型：
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作者：
Pasek, Matthew A.;Block, Kristin;Pasek, Virginia
闪电是由云对地闪电形成的天然玻璃。在以前的研究中已经报道了几种不同形态的fulfulte，包括砂fulfulte，岩石fulfulte和粘土fulfulte。在这里，我们研究了沙子、粘土和钙质电流石，并证明了它们在形态上有系统的不同。我们进一步利用形态特征来约束电火花形成雷击的性质。我们将电流石分为四种形态类型，外加一种次要类型。I型fulgurte是由薄玻璃墙组成的砂状fulgurte；II型电流石为粘土型电流石，由厚的富熔体壁组成；III型fulgurte是caliche fulgurte，由厚的玻璃质弱壁组成；IV型电流石是岩石电流石，由玻璃组成，其壁由周围未熔化的岩石组成。电闪体形态表明，电闪体形成的能量在1 ~ 30 MJ/m之间，表明加热速率在1000 K/s左右，闪电通道直径约为1 mm。在大多数电闪石中，闪电会产生至少两种成分的混合物：一种被认为是电闪石的二氧化硅玻璃和一种成分更多样化的地面物质。除了这四种主要类型之外，第五种类型-液滴型-在形态上与其他类型不同，但在成分上与II型或IV型有关。此外，来自美国宾夕法尼亚州约克县的两种fulgurites显示，铁被Fe- ti和Si-P化合物还原为铁金属，其化学计量范围从几乎纯的铁金属到FeSi。这些金属硅化物包括化学计量的Fe3Si， Fe2Si, Fe5Si3，可能还有Fe8Si3和Fe7Si3，并为这些相提供了地球来源，这些相通常与外星物质有关。
Fulgurites are natural glasses formed by cloud-to-ground lightning. Several different morphologies of fulgurites have been reported in previous studies, including sand fulgurites, rock fulgurites, and clay fulgurites. Herein, we examine sand, clay, and caliche fulgurites and demonstrate that these differ systematically in their morphology. We further use morphological features to constrain properties of fulgurite-forming lightning strikes. We classify fulgurites into four types of morphologies with an additional minor type. Type I fulgurites are sand fulgurites consisting of thin, glass walls; type II fulgurites are clay fulgurites, consisting of thick, melt rich walls; type III fulgurites are caliche fulgurites, consisting of thick, glass poor walls; and type IV fulgurites are rock fulgurites, consisting of glasses with walls consisting of surrounding, unmelted rock. Fulgurite morphology shows that the energy of fulgurite-forming strikes is between 1 and 30 MJ/m of fulgurite formed, suggests heating rates in the order of 1,000 K/s, and lightning channel thicknesses of about 1 mm diameter. Lightning generates mixtures of at least two components in most fulgurites: an SiO2 glass identified as lechatelierite and a groundmass of more varied composition. In addition to these four primary types, a fifth type-droplet fulgurites-is morphologically dissimilar from the other types, but is compositionally related to the type II or IV fulgurites. Additionally, two fulgurites, both from York County, Pennsylvania, USA, showed the reduction of iron to iron metal with an assortment of Fe-Ti and Si-P compounds with stoichiometry that ranges from nearly pure Fe metal to FeSi. These metal silicides include stoichiometric Fe3Si, Fe2Si, and Fe5Si3, and possibly Fe8Si3 and Fe7Si3, and provide a terrestrial source for these phases, which are typically associated with extraterrestrial material.