9. Critique of article: "The effect of thermal stress on radiohalos in biotites," by Mark Armitage: American Laboratory, November, 1997, volume 29, number 22, pages 25-33.
Kurt Hollocher
email: hollochk@union.edu
American Laboratory
P.O. Box 3220
Lowell, MA 01853-9878
Dear Editor:
I wish to comment on the article "The effect of thermal stress on radiohalos in biotites," by Mark Armitage: American Laboratory, November, 1997, volume 29, number 22, pages 25-33. In contrast to typical American Laboratory articles, this article presents no new material and shows little understanding on the part of the author of fundamentals of the problem addressed.
1. The title is misleading. The fading of radiation halos from biotite at elevated temperatures has nothing to do with stress, thermal or otherwise, but rather is an atomic-scale annealing process.
2. The mention on page 25 of "electron microprobe mass spectrometry analysis" is a mistake; there is no such analytical instrument.
3. The author implies that the halos around radioactive inclusions formed "in the absence of any apparent microcracks or clefts in the biotite crystals." In fact, the color fringes (Newton's rings), obvious in Figures 4, 5, 8, 10, 15, and 15, are caused by reflection interference on cracks along the {001} cleavage of biotite. Most figures also show cracks in other orientations. His samples, therefore, contain numerous microcracks. The author's technique (optical microscopy and crystals lying flat on the stage on their cleavage surfaces) cannot identify cleavage-parallel cracks thinner than about 1/2 wavelength of visible light, or cracks in other directions thinner than about 1/4 wave length. His observations, therefore, do not "rule out the solutions-migrating-along-microcracks theory for the origin of these...radiohalos."
4. The author is wrong stating that granites crystallize at 1200 to 2000 degrees C. Most granites and similar rocks become solid at temperatures of 650 to 850 degrees C or so, depending on pressure and chemical composition. Some form at lower temperatures.
5. The author is wrong portraying "enormous batholiths (some as long as 1,600 km)" as having crystallized from a single body of magma. Such batholiths are composite masses of igneous rock that typically formed over tens of millions of years by emplacement of hundreds or thousands of smaller bodies of magma.
6. The author makes much of the necessarily slow cooling rates of large bodies of magma deep in the crust, but made no effort to estimate actual crystallization temperatures or cooling rates of the rock bodies from which his biotites were derived. The author claims that his samples come from two pegmatites, a calcite vein, and a nepheline pegmatite (and another sample of unknown origin). First, it is clear that some, possibly all, of the biotite host rocks were not granites. More importantly, it is clear that these are all small bodies that may have cooled many orders of magnitude faster than he suggests for giant granite bodies. In addition, many pegmatites and calcite veins were precipitated by aqueous solutions at temperatures well below those of silicate magmas. His discussion, therefore, of cooling from magmatic temperatures "possibly taking tens of millions of years" is irrelevant.
7. The physical effects of heating biotite in air are not new. Heating hydrated minerals in air has several well-known effects, including loss of water with physical crumbling of the mineral (decrepitation or "flaking"), oxidation of iron, and consequent damage to the crystal lattice. Iron oxidation darkens biotite due to enhanced Fe2+-Fe3+ charge transfer absorption, and by precipitation of dark secondary minerals such as magnetite.
8. The experiments are poorly designed. All biotite in all igneous rocks, including granite, crystallized at high pressure, high H2O fugacity, and low O2 fugacity. The author's experiments involved heating in air (low pressure, low fH2O, high fO2), and do not mimic the effects of elevated temperatures deep in the crust. On page 32 the author states that "Few, if any, of the micas inspected ... for this study exhibited such marked heat related effects. It follows, therefore, that the biotites ... must not have been subjected to elevated temperatures for protracted periods since formation of the radiohalos." This conclusion, based on heat damage in his experiments, has no foundation because of the unrealistic nature of his experiments.
9. Most figures describe the radiation halos as being "Polonium 218 [or 210] radiohalos." This interpretation is not supported by any data in this paper, not even accurate scales on the photographs that might allow the reader to measure halo radii. Further, to an untrained reader only Figure 12 has a halo that is, perhaps, readily identifiable. Although I have never studied them in detail, I have seen many thousands of U and Th decay series radiation halos in biotite and other minerals during my normal petrographic work. Despite my decades of experience, I can confidently identify radiation halos only in Figures 8, 9 (see below), 12, and 14. Which, if any, of the fuzzy dark spots in the other figures are radiation halos is unclear. It is certainly not clear that any of the halos owe their existence to Polonium 218 or 210.
10. Erasure of radiation damage at elevated temperatures is not new. It has long been known that elevated temperatures anneal radiation damage in a variety of materials. Indeed, this process is in common use as a geologic tool for understanding the thermal history of rocks. The rate of thermal erasure of alpha particle and spontaneous fission radiation damage has been well documented and characterized for many minerals, contrary to the implication in the last paragraph on page 33.
11. On page 31 the statement is made that "Landmarks within the samples underwent significant changes, either by full fracturing, flaking, and splitting within the biotite or by complete darkening." This clearly indicates that "landmarks" in the biotite crystals (cracks and non-radiation halos spots) did not heal and vanish during heating. In contradiction, the caption of Figure 5 states that "...after heating to 600 degrees C.... Large landmarks have been erased," as though the cracks and spots had healed. A similar contradictory statement is made on page 32. Removal of a landmark by flaking away part of the crystal is not the same as erasure by healing or annealing.
12. The documentation of the author's experiments is very shoddy.
A. Figure 1, because it is dark and at low magnification, does not show radiation halos as the caption suggests.
B. Although the effects of heating in air (decrepitation and darkening) are visible in Figures 2 and 3, they are not clearly the same fields of view and so cannot be readily compared.
C. Figures 4 and 5, and related text, purport to show that "large landmarks have been erased" by heating. Oddly, no landmarks (cracks and spots) appear similar in the two photographs, suggesting that they are not the same field of view. Figures 3, 9, 11, 15, and 17 demonstrate that more large landmarks (decrepitation and other damage) are expected in heated samples, not fewer. This contradiction is not adequately addressed.
D. Figures 6 and 7 supposedly show "Some halo ring erasure..." due to heating to 350 degrees C. Because they are not pointed out or clear, readers are forced to guess which fuzzy dark spots are radiation halos. However, in Figure 7 there exist many of the same fuzzy dark spots seen in Figure 6. Additionally, overexposure of Figure 7 make comparisons between Figure 6 and 7 difficult.
E. Figures 8 and 9 supposedly show that "The Polonium 210 halos have been erased" by heating up to 450 degrees C. However, if you take into account the fact that Figure 9 is inverted and rotated about 30 degrees clockwise with respect to Figure 8, the fuzzy spots are still present, and so the author's statements in the caption and in the text are wrong.
F. Figures 10 and 11 are enlargements of portions of Figures 2 and 3 and are supposed to show major damage to the biotite and erasure of halos. As stated above for Figures 2 and 3, Figures 10 and 11 are not obviously of the same field of view, so conclusions as to halo erasure cannot be made.
G. Figures 12 and 13 are said to show erasure of a radiation halo at 550 degrees C. The halo is obvious in Figure 12. However, as with Figures 4 and 5, no landmarks are similar in the two images, and so the photographs are likely to be of different fields of view. Conclusions are, therefore, impossible.
H. Figures 14 and 15 claim to show erasure of radiation halos at temperatures up to 700 degrees C. Although halos are obvious in Figure 14, I see no similar landmarks in the two photographs, including the "radiocenters" that purportedly "remain." It is unlikely that Figures 14 and 15 show the same field of view.
I. Figures 16 and 17 claim to show erasure of radiation halos after heating to 300 degrees C. Contrary to their captions, Figure 17 is obviously at half the magnification of Figure 16, and one is inverted relative to the other. It is unclear in Figure 16 which of the few fuzzy spots are supposed to be radiation halos, but comparison with Figure 17 is impossible anyway because lower magnification and heat damage obscure many regions where the spots supposedly no longer exist.
The implication on page 33 that these experiments "raise serious questions about the validity of the conventional wisdom of igneous, metamorphic, and/or hydrothermal processes of formation for these biotites and their host rocks" is silly. The high-temperature origin of igneous and metamorphic rocks, the relatively low-temperature origin of some pegmatites, veins, and some other igneous-like rocks, and the precipitation of radioactive and other minerals in cracks by aqueous solutions, have been demonstrated and supported by hundreds and thousands of man-years of work by geologists and others. These scientists have used techniques ranging from field studies and microscope petrography, to chemical analyses of rocks and minerals, and to laboratory experiments and thermodynamic calculations. A few experiments heating biotite in air, with results that in large part have been known for centuries, and in remaining part have been known for decades (since the origin of radiation halos was understood), do not raise "serious questions" of anything but the understanding Armitage has for his subject.
There are two other, perhaps more disturbing issues. This paper appears to be very similar to a paper published by Mark Armitage and Ed Back, 1994, "The thermal erasure of radiohalos in biotite," in Creation Ex Nihilo Technical Journal, v. 8, no. 2, p. 212-222. First, the American Laboratory article may represent double publication of the same material; a breach of scientific ethics. Second, Creation Ex Nihilo Technical Journal is a creationist publication that prints articles on so-called "creation science." I strongly suspect that Armitage's agenda in writing the American Laboratory article was not to present new science (which it does not do), but rather to couch in quasi-scientific terms his religious belief that modern geologic science (and hence all science) has questionable validity. This suspicion is supported by the fact that Armitage makes no reference to his article in Creation Ex Nihilo Technical Journal.
In conclusion, this article presents no new science, no useful or new experimental or analytical techniques, and no well-documented results or conclusions. I am surprised and saddened that this paper was accepted and published by American Laboratory.
Sincerely,
Kurt Hollocher
Dr. Kurt Hollocher Geology Department Union College Schenectady, NY 12308-2311 Tel: 518-388-6518 Fax: 518-388-6789 http://mallard.geology.union.edu