Natural glass occurs on Earth in different geological contexts, mainly as volcanic glass, fulgurites, and impact glass. All these different types of glasses are predominantly composed of silica with variable amounts of impurities, especially the alkalis, and differ in their water content due to their mode of formation. Distinguishing between different types of glasses, on Earth and also on the Moon and on other planetary bodies, can be challenging. This is particularly true for glasses of impact and volcanic origin. Because glass is often used for the determination of the age of geological events, even if out of geological context, as well as to derive pressure and temperature constraints, or to evaluate the volatile contents of magmas and their source regions, we rely on methods that can unambiguously distinguish between the different types of glasses. We used the case of the Cali glass, found in an extended area close to the city of Cali in western Colombia, which was previously suggested to be of impact or volcanic origin, to show that, using a multimethod approach (i.e., combining macroscopic observations, chemical and isotopic data, and H2O content), it is possible to distinguish between different formation modes. A suite of Cali glass samples was analyzed using electron microprobe, instrumental neutron activation analysis, thermal ionization mass spectrometry, and Fourier-transform infrared spectroscopy, allowing us to definitively exclude an impact origin and instead classify these glasses as a rhyolitic volcanic glass (obsidian). Our results suggest that other “unusual glass occurrences” that are claimed, but not convincingly proven, to be of impact origin should be reexamined using the same methodology as that applied here.Natural glass is rare on Earth compared to crystalline rocks due to its specific formation conditions and durability aspects (i.e., glass is metastable and easily altered). It is essential to distinguish between different types of glasses because of their use for dating of geological events, to evaluate the volatile abundances of magmatic source regions, to establish pressure and temperature constraints, and for many other applications. In particular, the distinction between volcanic glass versus impact glass can be challenging and may lead to erroneous interpretation of the geological context (French and Koeberl, 2010); the potential for misidentification of origin motivated our investigation of Cali glass (found in an extended area near the city of Cali in western Colombia) samples to unravel the origin of this “unusual” glass (Fig. 1). We show that, by combining a number of different analytical methods and following a relatively simple research methodological scheme, we can discriminate between a volcanic origin and an impact origin for the Cali glass. This proposed methodology could be applied to reconstruct the geological context of materials of disputed origin in the future.Natural glass on Earth is mostly volcanic, mainly obsidian and, less commonly, tachylyte (e.g., O’Keefe, 1984). Obsidian is generally brown to black or gray in color. It commonly exhibits flow banding and contains more or fewer small vesicles and/or crystalline inclusions (microlites and/or phenocrysts), such as feldspar, pyroxene, cristobalite, magnetite, hematite, and ilmenite. A significant compositional range is known for obsidians, with silica contents from 65 to 80 wt%, and relatively high alkali contents (e.g., Tykot, 2021, and references therein).Fulgurites are glasses formed when lightning strikes Earth's surface, generating extremely high temperatures that are able to locally melt and fuse rock, sand, or soil (e.g., Pasek et al., 2012). It is commonly found as glassy hollow tubes and, more rarely, as patches of glass on exposed rock surfaces. This type of glass is not discussed further here, because it can easily be recognized based on macroscopic observations alone and/or on the context of occurrence.Impact glasses are quenched melts formed by shock melting of target rocks during impact events (Stöffler, 1984; Dressler and Reimold, 2001). Due to their mode of formation, they are commonly associated with shock-metamorphosed minerals and rock fragments, and, in many cases, they contain trace amounts of a projectile component (e.g., Koeberl, 2014, and references therein). Impact glass occurs in breccia deposits within or outside the impact crater, in proximal ejecta, as glass bodies and particles in breccia, or in distal ejecta as glass particles, spherules, and as (micro)tektites. Tektites are distal impactites derived from the (near-)surface of the target rocks, with specific petrographic, chemical, and isotopic characteristics, as well as extremely low H2O content (e.g., Koeberl, 2014). They are a rare type of impact glass found in only a few distinct strewn fields on Earth, usually at hundreds to thousands of kilometers from their source crater (e.g., Koeberl, 2014). In general, they are up to a few centimeters in size, they are mainly black or green, and rarely brownish to grayish, and they commonly show a pitted or textured surface. Tektites, along with some other types of impact glasses, can resemble obsidian and thus are readily misidentified (Fig. 2).Water content is an important parameter for the distinction of the different types of glass; the typical range for tektites is 0.002–0.030 wt% H2O, whereas other types of impact glasses contain 0.008–0.130 wt% H2O, and even up to 0.166 wt% H2O for Libyan Desert Glass (Beran and Koeberl, 1997). Volcanic glasses, on the other hand, have typical H2O contents ranging from 0.07 wt% to 2 wt% H2O for obsidian (e.g., Stevenson et al., 2019, and references therein).Over the past 100 years or so, several glass samples found in a group of South American countries, including Peru, Bolivia, Ecuador, and Colombia, referred to as “americanites” in the literature (e.g., Martin, 1933), were described either as “tektites,” “possible tektites,” or “pseudo-tektites,” based on macroscopic aspects similar to confirmed tektites (Codazzi Lleras, 1925; Stutzer, 1926; Döring and Stutzer, 1928; Koomans, 1938; Martin and De Sitter-Koomans, 1956; Ocampo et al., 2017). One of these glasses, the so-called “Cali glass,” also referred to in the literature as “obsidians from Cali,” “calites,” “calitites,” “colombites,” “colombianites,” or “piedra de rayo” (i.e., “lightning stone”) (e.g., Merrill, 1911; Bellot-Gurlet et al., 2008; Ocampo et al., 2017), occurs in a relatively extensive area along the Cauca River Valley in the Valle del Cauca department, Colombia (Fig. 1). The area of occurrence is more than 200 km long and some 30–40 km wide, with the department capital city of Cali approximately located at the center-western part of it. First reported by von Humboldt in 1823 (“Ces obsidiennes de Popayan ont souvent la forme de larmes ou même de boules à la surface tuberculeuse.” [These obsidians from Popayan often have tear or ball shapes with a pitted surface.]; von Humboldt, 1823, p. 340), it was assumed to be an (unusual) type of obsidian by some authors, whereas others argued that it is a tektite (von Humboldt, 1823; Merrill, 1911; Codazzi Lleras, 1925; Stutzer, 1926; Martin, 1933; Martin and De Sitter-Koomans, 1956; Bellot-Gurlet et al., 2008; Ocampo et al., 2017). Ocampo et al. (2017) recently claimed that Cali glass is tektite glass, without any specific evidence, and in turn used it to “confirm” the impact origin of a buried 36 × 26 km diameter “crater” structure (for which no shock metamorphism evidence is reported) located in the Cauca subbasin at 3°15′N and 76°25′W, south-southeast of the city of Cali (Fig. 1). In addition, Ocampo et al. (2017) determined a weighted mean 40Ar/39Ar age of 3.25 ± 0.04 Ma (2σ) from three Cali glass samples.Two sets of Cali glass samples were investigated in this study, including seven samples from the Natural History Museum Vienna (NHMW, Austria) collection (donated in the 1980s by mineral dealer Franz Gross), where “Tektites, Cali, Colombia” is written on the original label, and three samples collected by A.P. Crósta and F. Iwashita in July 2018 at two locations west-southwest from the town of Jamundí (at 3.23639°N, 76.64500°W and 3.16972°N, 76.66278°W; Fig. 1). Macroscopic investigations were conducted on all samples. Five of them were cut, and polished thick sections were prepared. The cutting of the different samples (especially the largest ones) proceeded without any problem, whereas tektites frequently shatter during cutting due to internal residual stress release. Petrographic investigations were completed by optical microscope and a JEOL JSM-6610 scanning electron microscope at the NHMW. Major-element compositions were measured for five samples at the NHMW using a JEOL JXA-8530-F field-emission-gun electron microprobe. Major- and trace-element abundances were obtained for three samples by instrumental neutron activation analysis (INAA) at the University of Vienna. Sr and Nd isotopic compositions were obtained for the same three samples by thermal ionization mass spectrometry at the University of Vienna. Finally, the H2O content of three double-polished samples was determined using Fourier-transform infrared spectroscopy (FTIR) at the University of Vienna. Additional information on our methods is given in the Supplemental Material1.Cali glass samples are generally associated with paleosurfaces covered by residual soil and/or in alluvial/colluvial deposits. In some cases, they are found at the surface, left as resistant remnants on top of the soil. The investigated samples are dark brown and gray to black in color, with sizes ranging from 2 to 5 cm (Figs. 2B and Fig. 2D; Fig. S1 in the Supplemental Material). Rare larger samples are also found (Fig. 2C). Mainly spheroidal, oval, or somewhat irregular in shape (with flattened portions), they show a heavily pitted surface (Figs. 2B–Fig. 2D; Fig. S1). One of the samples is dumbbell-like in shape (“Cali-1”; Fig. S1). A few of the samples show some layering. In transmitted light, the glass is pale gray to pale brown in color. A few small vesicles and mineral inclusions occur, including silica, feldspar, iron oxides, zircon, and apatite (Fig. 2F; Fig. S2). One of the samples shows alternating layers with numerous (preferentially aligned) microlites (Fig. 2E; Fig. S2).Microprobe investigations showed that the glass is chemically homogeneous in composition (Fig. 3A; Table S1). The samples show no major variations in composition at the scale of one sample (not even in the case of the layered sample investigated; Figs. 2D and Fig. 2E) or between different samples. This was also confirmed by the INAA data (Table S2). Compositional ranges for major-element microprobe data (in wt%) for five samples and for trace elements (Cr, Co, Rb, Sr, Zr, and Ba, in ppm), as determined with INAA for three samples, are: SiO2 (76.4–78.0), Al2O3 (12.2–12.8), TiO2 (below detection limit [bdl] to 0.19), FeO (0.46–0.59), MnO (bdl–0.08), MgO (0.04–0.09), CaO (0.60–0.66), Na2O (3.87–4.17), K2O (4.64–4.96), Cr (4.2–7.7), Co (0.3–0.4), Rb (168–195), Sr (60–67), Zr (207–254), and Ba (300–367). Figure 3A shows that the K2O + NaO contents of the Cali glass are much higher than values for all known tektites, but they are in the range known for obsidians from Colombia and Ecuador (cf. Bellot-Gurlet et al., 2008). The same is also true for other major and trace elements, for which abundances are similar to those in obsidians from this region (Fig. 3B).The three samples for which we obtained Sr and Nd isotopic compositions (Table S3), with epsilon Nd (εNd) values between 2.0 and 2.1 and εSr values between 2.4 and 2.7, showed a mantle signature, whereas all known tektites are characterized by a continental crustal signature (Fig. 4).In terms of water content, using the same calibration as in Beran and Koeberl (1997), the resulting H2O concentrations for the three investigated samples, i.e., Cali-1, Cali-2, and Cali-3, were 0.39, 0.56, and 0.48 wt% (±5 rel%), respectively. These values were obtained using the broad band at 3800–2550 cm–1 with a maximum at 3577 cm–1 (i.e., the band containing the O-H stretching fundamentals of both OH and H2O units in the glass) as visible on the FTIR absorption spectra reported in Figure S3. Water concentrations were obtained using this band in two different ways, and also using the very weak bands at 4515 cm–1 and 5230 cm–1, based upon the work by Persikov et al. (2014). The three different methods gave very similar results (see Table S4 and the Supplemental Material for details). The obtained values, ranging from 0.4 to 0.6 wt% H2O, are typical for obsidians and significantly higher, by one to two orders of magnitude, than water concentrations for tektites and other impact glasses (e.g., Beran and Koeberl, 1997; Stevenson et al., 2019).The confirmation of an impact origin for a given glass sample, or glass occurrence, can be challenging. Several examples other than the Cali glass have been suggested to be of impact origin, such as the Edeowie glass in South Australia (Haines et al., 2001), or the Dakhleh glass in the Western Desert of Egypt (Osinski et al., 2007), but their origins remain controversial.Based on their main visual characteristics, color, shape, and pitted surface, Cali glasses (Figs. 2B–Fig. 2D) are very similar to, and hardly distinguishable from, known tektites (Fig. 2A); however, they also look like typical obsidian samples that were subjected to corrosion.The petrographic characteristics of the studied samples, such as the presence of layering and microlites, the chemical compositions, with extremely low FeO content and high K2O + NaO contents (Fig. 3A), and the Nd and Sr isotopic ratios, typical of a mantle signature (Fig. 4; Table S3), are characteristic for volcanic origin and unlike known tektites.Our water concentration data, ranging from 0.4 to 0.6 wt% H2O, typical for obsidians, further allow us to definitely exclude an impact origin for the Cali glass. Furthermore, if the Cali glass were to be considered as a tektite, it should not occur in close proximity to its (assumed) source crater (Fig. 1), as claimed by Ocampo et al. (2017).The confirmation that Cali glass is a rhyolite volcanic glass (obsidian) corroborates the geographic location in which it is found. The Cauca River Valley is located between the Western and Central Colombian Cordilleras, two mountain ranges with numerous active and inactive volcanos. Therefore, we conclude that the Cali glass was produced in a volcanic eruption during the Pliocene (based on the age estimate from Ocampo et al., 2017), deposited relatively close to its source, and then subjected to dissolution, erosion, and fluvial processes in a tropical environment, explaining its current distribution over a relatively large area (Fig. 1).With our new data set, we can end the more than one-century-long debate on the origin of the Cali glass. Our straightforward analytical methodology is also suitable for examining other “unusual glass occurrences,” as well as glass samples returned to Earth from the Moon and future Mars missions, in order to determine the geological process(es) at the origin of their formation.This paper is dedicated to the memory of the American geologist George P. Merrill (1854–1929) for his early work on Cali glass and in the quest to follow the inscription on his gravestone, “Search for truth is the noblest occupation of man, its publication a duty” (a quote originally from Madame de Stael). We thank G. Batic for sample preparation. B. Gruber, D. Mader, and D. Topa are acknowledged for assistance in the acquisition of some data used in this study. We appreciate the constructive reviews from A. Cavosie, P. Hill, and an anonymous reviewer, as well as the suggestions and editorial handling from U. Schaltegger. A.P. Crósta acknowledges a “Silla Sanford” visiting scholar grant from the Universidad de los Andes, Bogotá, Colombia.

中文翻译：

---

区分火山玻璃和冲击玻璃——以卡利玻璃为例（哥伦比亚）

地球上的天然玻璃存在于不同的地质环境中，主要是火山玻璃、电闪石和撞击玻璃。所有这些不同类型的玻璃主要由含有不同量杂质（尤其是碱金属）的二氧化硅组成，并且由于形成方式不同，其含水量也不同。区分地球上、月球上和其他行星上的不同类型的眼镜可能具有挑战性。对于撞击和火山起源的玻璃来说尤其如此。因为玻璃通常用于确定地质事件的年龄，即使是在地质背景之外，以及推导出压力和温度限制，或评估岩浆及其源区的挥发性成分，我们依赖可以明确区分不同类型眼镜的方法。我们使用了在哥伦比亚西部卡利市附近的扩展区域发现的卡利玻璃的案例，该地区之前被认为是撞击或火山起源的，以表明，使用多方法方法（即结合宏观观察、化学和同位素数据以及 H2O 含量），可以区分不同的形成模式。使用电子微探针、仪器中子活化分析、热电离质谱和傅里叶变换红外光谱分析了一套 Cali 玻璃样品，使我们能够明确排除撞击源，并将这些玻璃归类为流纹岩火山玻璃（黑曜石） . 我们的结果表明，其他声称但没有令人信服地证明是撞击起源的“不寻常的玻璃事件”应该使用与此处应用的相同的方法进行重新检查。 与结晶岩相比，天然玻璃在地球上是罕见的，因为它具有特殊性形成条件和耐久性方面（即，玻璃是亚稳态的并且容易改变）。区分不同类型的玻璃是必不可少的，因为它们用于地质事件的测年、评估岩浆源区的挥发性丰度、建立压力和温度限制以及许多其他应用。特别是，火山玻璃与撞击玻璃之间的区别可能具有挑战性，并可能导致对地质背景的错误解释（French 和 Koeberl，2010）；原产地错误识别的可能性促使我们对卡利玻璃（在哥伦比亚西部卡利市附近的一个扩展区域发现）样本进行调查，以解开这种“不寻常”玻璃的来源（图 1）。我们表明，通过结合多种不同的分析方法并遵循相对简单的研究方法方案，我们可以区分卡利玻璃的火山起源和撞击起源。这种提议的方法可用于在未来重建有争议的材料的地质背景。地球上的天然玻璃主要是火山岩，主要是黑曜石，不太常见的是速溶玻璃（例如，O'Keefe，1984）。黑曜石一般呈棕色至黑色或灰色。它通常表现出流动带，并包含更多或更少的小泡和/或结晶包裹体（微晶石和/或斑晶），例如长石、辉石、方石英、磁铁矿、赤铁矿和钛铁矿。黑曜石的成分范围很广，二氧化硅含量为 65% 至 80%，碱含量相对较高（例如，Tykot，2021 和其中的参考文献）。 萤石是闪电击中地球表面时形成的玻璃，产生极高的温度能够局部熔化和融合岩石、沙子或土壤（例如，Pasek 等，2012）。它通常以玻璃状空心管的形式出现，更罕见的是，在裸露的岩石表面上出现玻璃碎片。这种类型的玻璃在这里不再进一步讨论，因为它可以很容易地仅基于宏观观察和/或发生的背景来识别。撞击玻璃是在撞击事件期间由目标岩石的冲击熔化形成的淬火熔体（Stöffler，1984 年；Dressler 和 Reimold，2001 年）。由于它们的形成方式，它们通常与冲击变质的矿物和岩石碎片有关，并且在许多情况下，它们包含微量的弹丸成分（例如，Koeberl，2014 年，以及其中的参考文献）。撞击玻璃出现在撞击坑内外的角砾岩沉积物中，在近端抛射物中，作为角砾岩中的玻璃体和颗粒，或在远端抛射物中以玻璃颗粒、球粒和（微）tektites 的形式出现。Tektites 是来自目标岩石（近）表面的远端撞击岩，具有特定的岩相、化学和同位素特征，以及极低的 H2O 含量（例如，Koeberl，2014 年）。它们是一种罕见的撞击玻璃，仅在地球上少数几个不同的散布区域中发现，通常距离它们的源陨石坑数百到数千公里（例如，Koeberl，2014）。一般来说，它们的大小可达几厘米，它们主要是黑色或绿色，很少呈褐色至灰色，它们通常显示有麻点或纹理的表面。Tektites 以及一些其他类型的抗冲击玻璃可能类似于黑曜石，因此很容易被误认（图 2）。水含量是区分不同类型玻璃的重要参数；tektites 的典型范围是 0.002–0.030 wt% H2O，而其他类型的冲击玻璃包含 0.008–0.130 wt% H2O，甚至利比亚沙漠玻璃的 H2O 高达 0.166 wt%（Beran 和 Koeberl，1997）。火山眼镜，另一方面，黑曜石的典型 H2O 含量为 0.07 wt% 至 2 wt% H2O（例如，Stevenson 等人，2019 年，以及其中的参考文献）。在过去 100 年左右的时间里，在包括秘鲁、玻利维亚、厄瓜多尔和哥伦比亚在内的一组南美国家在文献中被称为“美洲人”（例如 Martin，1933 年），被描述为“tektites”、“可能的 tektites”或“伪- tektites”，基于类似于已确认的 tektites 的宏观方面（Codazzi Lleras，1925；Stutzer，1926；Döring 和 Stutzer，1928；Koomans，1938；Martin 和 De Sitter-Koomans，1956；Ocampo 等，2017）。其中一种玻璃，即所谓的“卡利玻璃”，在文献中也称为“卡利黑曜石”、“calites”、“calitites”、“colombites”、“colombianites”或“piedra de rayo”（即，“闪电石”）（例如，美林，1911 年；Bellot-Gurlet 等人，2008 年；Ocampo 等人，2017 年），发生在哥伦比亚 Valle del Cauca 省考卡河谷沿线的一个相对广泛的地区（图 1）。产区长200多公里，宽约30-40公里，省会城市卡利大约位于其中西部。von Humboldt 于 1823 年首次报道（“Ces obsidiennes de Popayan ont souvent la forme de larmes ou même de boules à la surface tuberculeuse。”[这些来自 Popayan 的黑曜石通常呈泪珠状或球形，表面有凹痕。]；von Humboldt， 1823, p. 340)，一些作者认为它是一种（不寻常的）黑曜石，而其他人则认为它是一种陨石（von Humboldt, 1823; Merrill, 1911; Codazzi Lleras, 1925; Stutzer, 1926;马丁，1933 年；马丁和德西特-库曼斯，1956 年；Bellot-Gurlet 等人，2008 年；奥坎波等人，2017 年）。奥坎波等人。（2017）最近声称卡利玻璃是tektite玻璃，没有任何具体证据，并反过来用它来“确认”埋藏的直径36×26公里“火山口”结构的撞击起源（对此没有报道冲击变质证据) 位于卡利市东南偏南 3°15'N 和 76°25'W 的 Cauca 子盆地（图 1）。此外，奥坎波等人。(2017) 从三个 Cali 玻璃样品中确定了 3.25 ± 0.04 Ma (2σ) 的加权平均 40Ar/39Ar 年龄。本研究调查了两组 Cali 玻璃样品，包括来自维也纳自然历史博物馆（NHMW，奥地利）的七个样品) 藏品（1980 年代由矿物交易商 Franz Gross 捐赠），原标签上写着“Tektites, Cali, Colombia”，美联社收集了三个样品 Crósta 和 F. Iwashita 于 2018 年 7 月在 Jamundí 镇西南偏西的两个位置（北纬 3.23639°、西经 76.64500°和北纬 3.16972°、西经 76.66278°；图 1）。对所有样品进行了宏观研究。其中五个被切割，并制备抛光的厚切片。不同样品（尤其是最大样品）的切割没有任何问题，而在切割过程中，由于内部残余应力释放，玻璃陨石经常破碎。岩石学研究是通过光学显微镜和 NHMW 的 JEOL JSM-6610 扫描电子显微镜完成的。使用 JEOL JXA-8530-F 场发射枪电子微探针在 NHMW 处测量了五个样品的主要元素组成。在维也纳大学通过仪器中子活化分析 (INAA) 获得了三个样品的主要元素和微量元素丰度。在维也纳大学通过热电离质谱法获得了相同三个样品的 Sr 和 Nd 同位素组成。最后，在维也纳大学使用傅里叶变换红外光谱 (FTIR) 测定了三个双抛光样品的 H2O 含量。关于我们方法的其他信息在补充材料 1 中给出。Cali 玻璃样品通常与被残余土壤和/或冲积/崩积沉积物覆盖的古地表有关。在某些情况下，它们存在于地表，作为抗性残留物留在土壤顶部。被调查样品呈深棕色和灰色至黑色，尺寸范围为 2 至 5 厘米（图 3 和图 2）。图2B和图2D；补充材料中的图 S1）。还发现了罕见的较大样本（图 2C）。主要是球形、椭圆形或形状有些不规则（带有扁平部分），它们显示出严重的凹坑表面（图 2B-图 2D；图 S1）。其中一个样品呈哑铃状（“Cali-1”；图 S1）。一些示例显示了一些分层。在透射光下，玻璃呈浅灰色至浅棕色。出现一些小囊泡和矿物包裹体，包括二氧化硅、长石、氧化铁、锆石和磷灰石（图 2F；图 S2）。其中一个样品显示了具有许多（优先排列的）微晶石的交替层（图 2E；图 S2）。微探针研究表明，玻璃的化学成分是均匀的（图 3A；表 S1）。样品在一个样品的范围内（甚至在所研究的分层样品的情况下也没有；图 2D 和图 2E）或不同样品之间的成分没有显着变化。INAA 数据也证实了这一点（表 S2）。五个样品的主要元素微探针数据（重量百分比）和痕量元素（Cr、Co、Rb、Sr、Zr 和 Ba，单位为 ppm）的成分范围，由三个样品的 INAA 确定，为： SiO2 ( 76.4–78.0)、Al2O3 (12.2–12.8)、TiO2（低于检测限 [bdl] 至 0.19）、FeO (0.46–0.59)、MnO (bdl–0.08)、MgO (0.04–0.09)、CaO (0.66) )、Na2O (3.87–4.17)、K2O (4.64–4.96)、Cr (4.2–7.7)、Co (0.3–0.4)、Rb (168–195)、Sr (60–67)、Zr (207–254) ，和巴（300-367）。图 3A 显示卡利玻璃的 K2O + NaO 含量远高于所有已知的陨石的值，但它们在以来自哥伦比亚和厄瓜多尔的黑曜石而闻名的范围内（参见 Bellot-Gurlet 等人，2008 年）。其他主要和微量元素也是如此，其丰度与该地区黑曜石的丰度相似（图 3B）。我们获得 Sr 和 Nd 同位素组成的三个样品（表 S3），与 epsilon Nd (εNd) 值介于 2.0 和 2.1 之间，εSr 值介于 2.4 和 2.7 之间，显示出地幔特征，而所有已知的陨石都具有大陆地壳特征（图 4）。在含水量方面，使用与根据 Beran 和 Koeberl (1997)，三个研究样品（即 Cali-1、Cali-2 和 Cali-3）的 H2O 浓度分别为 0.39、0.56 和 0.48 wt%（±5 rel%）。这些值是使用 3800-2550 cm-1 的宽带获得的，最大值在 3577 cm-1（即，包含玻璃中 OH 和 H2O 单元的 OH 拉伸基本原理的带），如在 FTIR 吸收光谱上可见在图 S3 中报告。根据 Persikov 等人的工作，使用该波段以两种不同的方式获得水浓度，并且还使用 4515 cm-1 和 5230 cm-1 处的非常弱的波段。(2014)。三种不同的方法给出了非常相似的结果（详见表 S4 和补充材料）。获得的值范围为 0.4 至 0.6 wt% H2O，对于黑曜石来说是典型的，并且比 tektites 和其他抗冲击玻璃的水浓度高出一到两个数量级（例如，Beran 和 Koeberl，1997 年；Stevenson 等人., 2019)。确认给定玻璃样品的冲击起源或玻璃发生可能具有挑战性。除了卡利玻璃之外，还有几个例子被认为是撞击源，例如南澳大利亚的 Edeowie 玻璃（Haines 等人，2001 年）或埃及西部沙漠中的 Dakhleh 玻璃（Osinski 等人，2007 年） ），但它们的起源仍然存在争议。基于它们的主要视觉特征、颜色、形状和凹坑表面，卡利玻璃（图 2B-图 2D）与已知的陨石（图 2A）非常相似，并且几乎无法区分); 然而，它们看起来也像典型的受到腐蚀的黑曜石样品。 研究样品的岩相特征，如层状和微晶石的存在，化学成分，FeO含量极低，K2O+NaO含量高（图3）。 3A), 以及地幔特征的典型 Nd 和 Sr 同位素比率（图 4；表 S3）是火山起源的特征，与已知的陨石不同。我们的水浓度数据范围为 0.4 至 0.6 wt% H2O，典型的黑曜石，进一步让我们明确排除卡利玻璃的撞击来源。此外，如 Ocampo 等人声称的那样，如果将卡利玻璃视为一种陨石，它不应出现在其（假设的）源陨石坑附近（图 1）。(2017). 卡利玻璃是一种流纹岩火山玻璃（黑曜石）的确认证实了它被发现的地理位置。考卡河谷位于哥伦比亚西部和中部科迪勒拉山脉之间，这两座山脉拥有众多活火山和非活火山。所以，我们得出的结论是，卡利玻璃是在上新世的火山喷发中产生的（基于 Ocampo 等人的年龄估计，2017 年），沉积在相对靠近其源头的位置，然后在热带环境，解释了它目前在一个相对较大区域的分布（图 1）。有了我们的新数据集，我们可以结束长达一个多世纪的关于卡利玻璃起源的争论。我们简单的分析方法也适用于检查其他“不寻常的玻璃事件”，以及从月球和未来的火星任务返回地球的玻璃样本，以确定它们形成起源的地质过程。这篇论文是为了纪念美国地质学家 George P. 梅里尔 (1854-1929) 因其早期在卡利玻璃上的工作以及在他的墓碑上追寻铭文“寻找真理是人类最高尚的职业，其出版是一种责任”（引自德斯塔尔夫人的引述） . 我们感谢 G. Batic 的样品制备。感谢 B. Gruber、D. Mader 和 D. Topa 在获取本研究中使用的一些数据方面提供的帮助。我们感谢 A. Cavosie、P. Hill 和匿名审稿人的建设性评论，以及 U. Schaltegger 的建议和编辑处理。AP Crósta 承认哥伦比亚波哥大洛斯安第斯大学的“Silla Sanford”访问学者资助。我们感谢 G. Batic 的样品制备。感谢 B. Gruber、D. Mader 和 D. Topa 在获取本研究中使用的一些数据方面提供的帮助。我们感谢 A. Cavosie、P. Hill 和匿名审稿人的建设性评论，以及 U. Schaltegger 的建议和编辑处理。AP Crósta 承认哥伦比亚波哥大洛斯安第斯大学的“Silla Sanford”访问学者资助。我们感谢 G. Batic 的样品制备。感谢 B. Gruber、D. Mader 和 D. Topa 在获取本研究中使用的一些数据方面提供的帮助。我们感谢 A. Cavosie、P. Hill 和匿名审稿人的建设性评论，以及 U. Schaltegger 的建议和编辑处理。AP Crósta 承认哥伦比亚波哥大洛斯安第斯大学的“Silla Sanford”访问学者资助。