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the Creative Commons Attribution 4.0 License.
| 02 Jul 2026
George Perkins Merrill's Analyses of Chondrules and Chondritic Meteorites
Abstract. George Perkins Merrill (1854–1929) was the preeminent American meteoriticist of the first quarter of the 20th Century. He applied to that science his pioneering knowledge and skill in the petrographic analysis of chondritic meteorites. Throughout his long and distinguished career with the United States National Museum, now the Smithsonian Institution of Washington, D.C., Merrill authored over seventy publications on meteorites. While many of those contributions described new irons and stones which had come into the museum’s collection, a pair of papers concerning the origin of chondrules and the evidence for and causes of metamorphism of chondritic meteorites led directly to his selection as the second recipient of the J. Lawrence Smith Medal which was awarded by the National Academy of Sciences in 1922 for outstanding accomplishments in the study of meteorites. The origins, primary arguments, and subsequent reception of those two landmark papers are herein reviewed. Particular attention is given to how Merrill’s hypotheses on chondrule formation and the evidence for thermal and dynamic metamorphic alteration of chondrites have come to underpin and advanced modern understandings of the early history of the solar system.
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- AC1: 'Comment on hgss-2026-9', Carl Drummond, 07 Jul 2026
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RC1: 'Review of Drummond paper on Merrill', Alan E. Rubin, 24 Sep 2026
The paper is a competent summary of Merrill’s work on chondritic meteorites, placing it in its historical context. It is worthy of being published in HGSS. I have a number of minor comments.
Line 136. The first description of chondrules was not by Gustav Rose, but by Jacques-Louis, Comte de Bournon (1802) in a mineralogically descriptive paper associated with Edward Charles Howard’s chemical analyses of meteorites: Experiments and observations....
Line 162. What are the modern values for the petrologic types of the meteorites investigated by Merrill? If they were mainly type 4 (or 3) that would explain the paucity of plagioclase feldspar. This phase is essentially absent in type 3, and grains are tiny (perhaps <5 micrometers) in type 4.
Line 171. You should note that these are currently described as RP and C chondrule textural types.
Line 183. Similarly, these are now known as BO chondrules.
Line 205. What kind of rim is Sears referring to? Are these the crystalline rims around many BO chondrules? There are also several other types of rims with different origins: secondary shells in enveloping compound chondrules, igneous rims, and fine-grained matrix-like rims.
Line 256. The correct word is crystallization, not condensation.
Line 345. While it may be true that there close to four dozen phases identified in chondrules, this is very misleading. The principal primary minerals in >98% of chondrules in ordinary and carbonaceous chondrites are major olivine, low-Ca pyroxene and silico-feldspathic glass, minor to accessory Ca-pyroxene, kamacite, troilite, and accessory to trace merrillite and chromite. Metamorphism will introduce plagioclase and chromite. Enstatite-chondrite chondrules include additional and unusual phases, and terrestrial weathering will add more.
Line 348. The number of proposed mechanisms for forming chondrules is indeed no less than eight. Rubin (2000) Earth Sci. Rev. 50, 3-27, listed 14.
Table 2. spelling error: “Systeamatic”
Section 3.2.1 through 3.2.4 At the end of each section, give the modern equivalents of what these rocks are. It would make it easier to visualize what Merrill was looking at. Give the petrologic types, the chondrite groups, and if appropriate, the range of shock stages.
Line 492. Change trances to traces.
Line 547. Change head to heat.
Line 630. At the end of this section, it might be useful to tell readers that essentially no static (lithostatic) pressure is involved in chondrite formation.
Line 742: Roy Clarke had an “e” at the end of his last name. The citation in the text should also be corrected.
Citation: https://doi.org/10.5194/hgss-2026-9-RC1 -
RC2: 'Comment on hgss-2026-9', Alan E. Rubin, 24 Sep 2026
The paper is a competent summary of Merrill’s work on chondritic meteorites, placing it in its historical context. It is worthy of being published in HGSS. I have a number of minor comments.
Line 136. The first description of chondrules was not by Gustav Rose, but by Jacques-Louis, Comte de Bournon (1802) in a mineralogically descriptive paper associated with Edward Charles Howard’s chemical analyses of meteorites: Experiments and observations....
Line 162. What are the modern values for the petrologic types of the meteorites investigated by Merrill? If they were mainly type 4 (or 3) that would explain the paucity of plagioclase feldspar. This phase is essentially absent in type 3, and grains are tiny (perhaps <5 micrometers) in type 4.
Line 171. You should note that these are currently described as RP and C chondrule textural types.
Line 183. Similarly, these are now known as BO chondrules.
Line 205. What kind of rim is Sears referring to? Are these the crystalline rims around many BO chondrules? There are also several other types of rims with different origins: secondary shells in enveloping compound chondrules, igneous rims, and fine-grained matrix-like rims.
Line 256. The correct word is crystallization, not condensation.
Line 345. While it may be true that there close to four dozen phases identified in chondrules, this is very misleading. The principal primary minerals in >98% of chondrules in ordinary and carbonaceous chondrites are major olivine, low-Ca pyroxene and silico-feldspathic glass, minor to accessory Ca-pyroxene, kamacite, troilite, and accessory to trace merrillite and chromite. Metamorphism will introduce plagioclase and chromite. Enstatite-chondrite chondrules include additional and unusual phases, and terrestrial weathering will add more.
Line 348. The number of proposed mechanisms for forming chondrules is indeed no less than eight. Rubin (2000) Earth Sci. Rev. 50, 3-27, listed 14.
Table 2. spelling error: “Systeamatic”
Section 3.2.1 through 3.2.4 At the end of each section, give the modern equivalents of what these rocks are. It would make it easier to visualize what Merrill was looking at. Give the petrologic types, the chondrite groups, and if appropriate, the range of shock stages.
Line 492. Change trances to traces.
Line 547. Change head to heat.
Line 630. At the end of this section, it might be useful to tell readers that essentially no static (lithostatic) pressure is involved in chondrite formation.
Line 742: Roy Clarke had an “e” at the end of his last name. The citation in the text should also be corrected.
Citation: https://doi.org/10.5194/hgss-2026-9-RC2 -
RC3: 'Comment on hgss-2026-9', Dominik Hezel, 16 Oct 2026
This is an interesting paper on George Merrill’s significant contribution to the field of meteoritics. I would have enjoyed this even more, if Merrill’s contributions would be more connected to current knowledge. For example, Merrill’s insights would likely be amplified, if in chapter 3.2 it would be always clear, what meteorites Merrill was looking at, at least what type of meteorite in the modern classification. This is done only in places, e.g., lines 584 or 617. It might even be interesting to illustrate Merrill’s description in additional BSE-images, to make it even clearer, what Merrill was talking about. Such connections throughout the ms would make it much easier to follow Merrill’s insights, at least for me.
The 4 arguments in section 3.3 could be more structured or emphasised.
If available, it would of course be very interesting to know why Merrill assumed a ferrous chloride as the precursor of metallic components in chondrites. As Cl is quite a rare element, not only in chondrites.
I was a bit puzzled why Hazen was used as a main source. I would also recommend some more relevant literature, such as the reviews in the Chondrule book from 2018 (https://doi.org/10.1017/9781108284073), or the just published Evolution of the Solar System: Constraints from Meteorites (https://link.springer.com/book/9789402423686).
Some minor comments
- 323: hot -> not
- 354: Multiple mechanisms are in fact proposed for chondrule formation, cf. current reviews in Chondrules and ours, more specific Krot paper.
- 455: previous
- 519: I was waiting for the mentioning of merrillite, a common meteorite mineral, and that it was named in honour of Merrill. I find it sort of anticlimactic how this is introduced here, without clear mentioning it is named after Merrill. Contrary, ›maskelynite‹ gets a much better introduction in line 502f.
- 534: cataclastic
Citation: https://doi.org/10.5194/hgss-2026-9-RC3
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I received the following input from Professor Alan Rubin via email after I pointed him to this open source review process. I will, of course, fully address these extremely helpful comment.
Thanks for steering me toward your paper on George Merrill. I am frequently reminded of him when I encounter his eponymous mineral in chondrites. I have a few comments on this manuscript as well. Line
165: Anorthite is very rare in chondrules from type-3 chondrites. It really only shows up in grains >2 um in chondrites of type 5 and 6 (where the grains can exceed 50 um). Line 170. Radial pyroxene chondrules constitute about 8% of the chondrules in ordinary chondrites. Line 210. Compound chondrules are not equivalent to porphyritic chondrules. Most chondrules are porphyritic, so most compound chondrules are porphyritic as well. But, other chondrule textural types can form compound chondrules as well. We discussed this in a 1995 paper by Wasson et al. Line 323: not not hot. Line 575:
I'm not sure exactly what you are referring to as a marginal rind. It could be a bleached zone around many nonporphyritic chondrules due to parent-body aqueous alteration, or it could just be a thin fine-grained matrix-like rim around many chondrules in type-3 chondrites. Line 639: Interestingly, FeCl, lawrencite, is a primary phase (albeit a rare one) in enstatite chondrites.
I also want to note that some type-3 ordinary chondrites contain large irregular fragments of porphyritic chondrules that Bob Dodd first made me aware of. These have textures essentially identical to normal-size porphyritic chondrules and are likely just chondrule fragments, plausibly broken in the regolith prior to final whole-rock consolidation. I found that porphyritic chondrules are particularly friable when I tried to exhume them from their adhering matrix. This is the reason that many compositional studies of separated chondrules have much larger proportions of nonporphyritic samples. It is a selection effect of excavation.
Finally, I was a little surprised you did not cite John Burke's masterful 1986 work Cosmic Debris which is a fine study of the history of meteoritics.