We have investigated the fine‐grained matrix of the least‐altered unequilibrated ordinary chondrite (UOC) Semarkona (LL3.00) using different electron microscope techniques. Unlike previous studies, which found that the matrix of Semarkona was extensively altered to phyllosilicates, we have discovered the widespread occurrence of much more pristine amorphous silicates in the sample that we have studied. Detailed TEM study shows that these materials occur pervasively in the matrix as (1) continuous groundmass; (2) distinct, circular to subrounded features, which contain nanometric‐size sulfides and carbides; or (3) distinct objects containing parallel, linear features composed of sulfides and voids. These amorphous silicates have many textural and compositional similarities to the occurrences of amorphous silicates found in pristine carbonaceous chondrites (CCs); however, minor differences were also identified. Most of the textural and chemical differences suggest that these materials formed at different times and locations in the solar nebula, compared to matrix materials in CCs. Nevertheless, their occurrence suggests that the amorphous silicates in Semarkona formed by similar processes to those proposed for amorphous silicates in CCs, that is, rapid cooling that favored disequilibrium condensation of material evaporated during chondrule‐forming events. In addition, the occurrence of minimally altered amorphous silicates in Semarkona demonstrates that the effects of aqueous alteration, which have been widely described in this meteorite, are not pervasive. Instead, our new observations demonstrate that aqueous alteration has affected Semarkona heterogeneously and that locally, regions of much more pristine matrix that have escaped extensive alteration are still preserved within this meteorite. Such materials provide significant new insights into the pristine characteristics of ordinary chondrite matrix material that has not been previously available.

中文翻译：

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Semarkona基质中的无定形硅酸盐：最原始的普通球粒陨石中原始基质材料局部保存的第一个证据

我们使用不同的电子显微镜技术研究了变化最小的未平衡普通球粒陨石（UOC）Semarkona（LL3.00）的细颗粒基质。不同于先前的研究，后者发现Semarkona的基质已被广泛地改变为页状硅酸盐，我们发现在我们研究的样品中广泛存在着更多的原始无定形硅酸盐。详细的TEM研究表明，这些物质普遍存在于基质中，其表现为（1）连续的地面质量；（2）明显的，圆形到亚圆形的特征，其中包含纳米尺寸的硫化物和碳化物；（3）包含由硫化物和空隙组成的平行，线性特征的不同物体。这些无定形硅酸盐与原始碳质球粒陨石（CCs）中发现的无定形硅酸盐在结构和成分上有很多相似之处。但是，也发现了微小的差异。大多数结构和化学差异表明，与CC中的基质材料相比，这些材料在太阳星云中的不同时间和位置形成。然而，它们的发生表明，Semarkona中的无定形硅酸盐是通过类似于CC中无定形硅酸盐的拟议过程形成的，也就是说，快速冷却有利于在形成软骨的过程中蒸发的物质发生不平衡冷凝。此外，在Semarkona中发生了变化最小的无定形硅酸盐，这表明在该陨石中已广泛描述了水蚀作用的影响，不是普遍的。取而代之的是，我们的新观察结果表明，水相蚀变已异质地影响了Semarkona，并且在局部，逃脱了广泛变化的原始基质区域仍保留在该陨石中。此类材料为普通球粒陨石基质材料的原始特性提供了重要的新见解，而以前尚无法获得。