XII. On the microscopical structure of meteorites
XII. On the microscopical structure of meteorites
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十二．
DOI：
10.1098/rspl.1863.0075
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通讯作者：
H. Sorby
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作者：
H. Sorby
在过去的一段时间里，我一直在努力将我在研究地球岩石时所使用的原理应用于陨石的研究，正如我在各种论文中所描述的那样，特别是在晶体的微观结构（夸脱）上。。篇研究就是这么说的青烟。1858年，第14卷。453)。我在那篇文章中指出，晶体中“流体腔、玻璃腔、空腔或气腔”的存在使我们能够非常满意地确定晶体是在什么条件下形成的。还有一些其他的研究方法仍然需要大量的研究，必须进行大量的实验，这将占用大量的时间；然而，我不希望推迟公布某些事实，我现在打算简短地叙述一下，以后再加以扩展和完善。首先，必须指出的是，陨石中的橄榄石含有极好的“玻璃腔”，与瓦斯中的橄榄石中的相似，从而证明这种物质一度处于火成岩状态。橄榄石还含有“气腔”，就像在火山矿物中常见的那样，因此表明存在一些气体或蒸汽（Aussun, Parnallee）。为了清楚地看到这些空腔，需要精心准备的薄片和数百倍的放大倍率。在空腔中发现的玻璃状物质也与外部和晶体之间相遇，以这种方式表明它是形成它们的物质的非结晶残留物（Mezö-Madaras, Parnallee）。它呈紫红色或褐色，具有人造玻璃特有的结构和光学特性。陨石的一些孤立部分也具有与石质熔岩非常相似的结构，在那里，晶体的形状和相互关系证明它们是在原地凝固形成的。也许有些陨石应该被认为具有这种特性（斯坦恩，新康科德），但证据绝不是结论性的，在原地发生的结晶可能是次要的结果；而在其他情况下，组成粒子具有破碎碎片的所有特征（L’aigle）。这有时会使我们看到一种结构，非常像那种凝固的火山灰，的确，我有些标本，乍一看，很容易被误认为是陨石的碎片。由此看来，在陨石的物质熔化之后，相当一部分被分解成小碎片，随后被聚在一起，或多或少地被机械和化学作用固结，其中必须归类为铁的偏析，要么是金属状态，要么是与其他物质结合。显然，在某些情况下，当熔化的物质变成晶体时，就会发生分裂，但在其他情况下，粒子的形式使我得出结论，它在熔化时被分解成分离的小球（Mez Madaras, Parnallee）。这似乎就是在陨石中遇到的一些圆形颗粒的起源；因为它们偶尔仍含有相当数量的玻璃，而在其中形成的晶体是成组排列的，从外表面的一个或多个点向外辐射，这种方式表明它们是在碎片获得目前的球体形状之后形成的（Aussun等）。在这一点上，它们与在陆地岩石中发现的一般类型的凝结小球最具特点，它们从中心辐射，我所知道的唯一类似的情况是在斯卡伯勒的凯洛韦岩石中的某些鲕粒，它们经历了二次结晶。这些事实都完全独立于熔融的黑色地壳。
For some time past I have endeavoured to apply to the study of meteotes the principles I have made use of in the investigation of terrestrial cks, as described in my various papers, and especially in that on the microscopical structure of crystals (Quart. Journ. Geol. Soc. 1858, vol. xiv. 453). I therein showed that the presence in crystals of “fluid-, glass-, one-, or gas-cavities” enables us to determine in a very satisfactory manner nder what conditions the crystals were formed. There are also other ethods of inquiry still requiring much investigation, and a number of experiments must be made which will occupy much time; yet, not wishing postpone the publication of certain facts, I purpose now to give a short ccount of them, to be extended and completed on a subsequent occasion. In the first place it is important to remark that the olivine of meteorites ontains most excellent “glass-cavities,” similar to those in the olivine of avas, thus proving that the material was at one time in a state of igneous usion. The olivine also contains “gas-cavities,” like those so common in olcanic minerals, thus indicating the presence of some gas or vapour (Aussun, Parnallee). To see these cavities distinctly, a carefully prepared hin section and a magnifying power of several hundreds are required. The vitreous substance found in the cavities is also met with outside and amongst the crystals, in such a manner as to show that it is the uncrystalline residue of the material in which they were formed (Mezö-Madaras, Parnallee). It is of a claret or brownish colour, and possesses the characteristic structure and optical properties of artificial glasses. Some isolated portions of meteorites have also a structure very similar to that of stony lavas, where the shape and mutual relations of the crystals to each other prove that they were formed in situ, on solidification. Possibly some entire meteorites should be considered to possess this peculiarity (Stannern, New Concord), but the evidence is by no means conclusive, and what crystallization has taken place in situ may have been a secondary result; whilst in others the constituent particles have all the characters of broken fragments (L’Aigle). This sometimes gives vise to a structure remarkably like that consolidated volcanic ashes, so much, indeed, that I have specimens whic at first sight, might readily be mistaken for sections of meteorites. It wou therefore appear that, after the material of the meteorites was melted, considerable portion was broken up into small fragments, subsequently lected together, and more or less consolidated by mechanical and chemic actions, amongst which must be classed a segregation of iron, either in th metallic state or in combination with other substances. Apparently th breaking up occurred in some cases when the melted matter had becon crystalline, but in others the forms of the particles lead me to concluc that it was broken up into detached globules whilst still melted (Mez Madaras, Parnallee). This seems to have been the origin of some of th round grains met with in meteorites ; for they occasionally still contain considerable amount of glass, and the crystals which have been formed it are arranged in groups, radiating from one or more points on the extern surface, in such a manner as to indicate that they were developed after th fragments had acquired their present spheroidal shape (Aussun, &c.). I this they differ most characteristically from the general type of concretiona globules found in terrestrial rocks, in which they radiate from the centre the only case that I know at all analogous being that of certain ooliti grains in the Kelloways rock at Scarborough, which have undergone secondary crystallization. These facts are all quite independent of th fused black crust.