Wood Petrifaction: a New View of Permineralization and Replacement

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Article Wood Petrifaction: A New View of Permineralization and Replacement

George E. Mustoe ID

Geology Department, Western Washington University, Bellingham, WA 98225, USA; [email protected]; Tel.: +1-360-650-3582

Received: 21 October 2017; Accepted: 16 November 2017; Published: 20 November 2017

Abstract: Petrified wood has traditionally been divided into two categories based on preservation processes: permineralization (where tissues are entombed within a mineral-filled matrix) and replacement (where organic anatomical features have been replicated by inorganic materials). New analytical evidence suggests that for most petrified wood, permineralization and replacement are not independent processes; instead, both processes may occur contemporaneously during diagenesis. Infiltration of mineral-bearing groundwater may initially cause permineralization of cellular tissues, but the wood is undergoing gradual degradation. The degree of anatomical preservation thus depends on the relative rates of mineral precipitation and tissue destruction. Rapid rates of mineralization under relatively mild Eh and pH conditions favor the preservation of organic matter. These conditions appear to be more common for calcium carbonate deposition than for silicification, based on observations of fossil woods from many localities. Because of these preservational complexities, “mineralization” and “mineralized” are more accurate as general descriptive terms than “permineralization” and “permineralized”.

Keywords: paleobotany; permineralization; petriﬁed wood; replacement; siliciﬁcation

1. Introduction The popular description of petrified wood as “wood turned to stone” does not address the question of how buried plant tissue becomes mineralized. Petrifaction of wood has long been described as being the result of either of two very different mineralogic pathways. Permineralization is a phenomenon where the original cellular material becomes entombed when open spaces become filled with silica, calcium carbonate, or other minerals. These anatomical voids include cell lumen, vessel lumen, and intercellular spaces. Mineral-filled spaces may also include fractures, rot pockets, or insect galleries. Replacement is a process where the original organic constituents degrade during fossilization, allowing minerals to occupy spaces formerly occupied by cell walls. With replacement, anatomical features may remain visible because of color or textural variations in the mineral phase [1]. A third variant occurs when wood is completely destroyed prior to mineralization, producing an empty cavity. Later the filling of this mold with mineral matter results in a cast that preserves only the external surface morphology. Belief that wood petrifaction may result either from permineralization or replacement has long been perpetuated by teachers and textbook authors, but these explanations of wood silicification are seldom accompanied by supporting evidence. If permineralization is the mode of petrifaction, relict organic materials should be readily detectable; scarcity of organic matter in mineralized wood is evidence of replacement. This paper describes the use of optical microscopy, scanning electron microscopy, and thermal gravimetric analysis to investigate these phenomena. The results indicate that wood petrifaction commonly results from a combination of processes, and can seldom be accurately described using terminology that implies a single pathway. Permineralization is well documented for

Geosciences 2017, 7, 119; doi:10.3390/geosciences7040119 www.mdpi.com/journal/geosciences Geosciences 2017, 7, 119 2 of 17 plant tissues preserved in calcareous “coal balls”, modern hot spring sinter, and some fossiliferous cherts, and in these specimens significant amounts of relict organic matter may be preserved. In contrast, true permineralization is relatively rare in silicified wood, where visible evidence of cellular anatomy is the result of inorganic mineralization rather than actual tissue preservation. This paper focuses on wood petrified with silica and calcium carbonate; mineralization with calcium phosphate, pyrite, limonite, hematite, and other minerals will be considered in a later publication, but the basic hypotheses of permineralization and replacement apply to all petrified wood, regardless of mineralogy.

2. Historical Background The belief that wood petrifaction results from duel processes dates to the 1800s; early references were summarized by St. John [2]. The concept of replacement requires the destruction of the original wood, accompanied by deposition of minerals that preserve visual evidence of the cellular architecture. This explanation is complicated by the impossibility of molecule-for-molecule substitution of small silicic acid molecules for large organic molecules; the destruction of organic wood constituents accompanied by the simultaneous precipitation of inorganic minerals is a more complex process. In contrast, a more simple explanation can be made for permineralization, where the original tissue is entombed by precipitation of minerals. Stewart and Rothwell [3] provide this description: “Permineralization occurs when the soluble silicates, carbonates, iron compounds and so on infiltrate cells and spaces between them. The process is analogous to the embedding of plant and animal tissues when preparing them for sectioning and microscopic examination.” This description echoes declarations made in earlier paleobotany textbooks. In 1941, C.A. Arnold wrote: “Although the deposition of mineral substances within plant tissues is dependent upon the release of certain substances from the cell walls, there is no evidence of direct replacement of any of the unaltered organic constituents of the plant by the petrifying tissues.” [4]. Andrews later made a similar claim in 1961: “In the case of some fossil woods, the mineral matter may be dissolved out, using hydrofluoric acid with silicified specimens, leaving the original wood intact”[5]. The problem with these conjectures is the scarcity of supporting evidence. Petrifaction of plant tissues via cellular permineralization is well documented for calcareous coal balls, siliceous lagerstätten, and silica-encrusted wood in modern hot springs, as well as evidence from laboratory simulations. These phenomena are discussed in a later section of this paper. Otherwise, general acceptance of permineralization as the most popular explanation for wood petrifaction can be traced to a few early investigations. In 1927, St. John [2] attempted to analyze the role of replacement versus permineralization (which she referred to as “impregnation”) during wood petrifaction. She subjected sawn specimens of petrified wood to treatment with hydrofluoric acid, using optical microscopy to determine the possible presence of intact cellular tissues. Her published report described results obtained from four “typical” silicified specimens. Intact cellular tissue was observed in a specimen of black Eocene wood from the Yellowstone National Park, Wyoming, USA; no relict tissue was visible in silicified alder (Alnus) from an unknown locality, or from unidentified fossil wood from New Mexico, USA; two taxonomically unidentified samples from unknown locations both showed cellular preservation in some areas, but not in other portions of the same specimen. A fifth specimen, from Kansas, USA, was mineralized with calcite; treatment with hydrochloric acid revealed cellular tissue. St. John interpreted her experimental results to mean wood petrifaction could result from impregnation, replacement, or a combination of the two. Arnold [4] questioned the concept of “molecule by molecule replacement”, basing his skepticism on examination of Devonian Callixylon wood. He concluded that “a considerable amount of the original substance might remain, with silica merely present as a preserving medium filling the cell spaces and the intercellular spaces”. He observed that treatment of several small pieces of fossil wood with hydrofluoric acid resulted in residual fragments of very soft material. When this material was consolidated with Geosciences 2017, 7, 119 3 of 17 collodion, microtome slices revealed a well-preserved cell structure. Although Arnold’s study involved Geosciences 2017, 7, 119 3 of 17 only fossil wood from a single locality, the 300 million year age of the specimens suggests that organic specimensmatter can besuggests preserved that even organic after matter prolonged can burial.be preserved Indeed, Devonianeven afterCallixylon prolongedis consideredburial. Indeed, to be Devonianthe oldest-known Callixylon petrified is considered wood (Figure to be the1). oldest-known petrified wood (Figure 1).

Figure 1. Callixylon whiteanum, petrographic thin section, transverse orientation. Devonian, Woodford Figure 1. Callixylon whiteanum, petrographic thin section, transverse orientation. Devonian, Woodford Shale, OK, USA. This new thin section is similar to the specimen described in 1947 by Arnold [4], Shale, OK, USA. This new thin section is similar to the specimen described in 1947 by Arnold [4], showing dark carbonaceous cell walls enclosing silica-filled cell lumina. showing dark carbonaceous cell walls enclosing silica-ﬁlled cell lumina.

One of Arnold’s objections to the replacement model for wood petrifaction was his assertion that silicaOne does of not Arnold’s have an objections affinity tofor the organic replacement compound models; he for believed wood petrifaction that if such was an his affinity assertion existed, that silica does not have an affinity for organic compounds; he believed that if such an affinity existed, fossil wood would contain organosilicates rather than SiO2. Arnold also asserted that cellular material wouldfossil wood remain would preserved contain forever organosilicates because ratherthe primar thany SiO structural2. Arnold components, also asserted particularly that cellular cellulose, material wouldare extremely remain insoluble preserved [4]. forever because the primary structural components, particularly cellulose, are extremelyIn later years, insoluble Arnold’s [4]. subjective assumptions have been contradicted by experimental and observationalIn later years, evidence. Arnold’s Under subjective laboratory assumptions conditions, have cellulose been and contradicted lignin are by soluble experimental only under and ratherobservational extreme evidence. chemical Underconditions, laboratory but in conditions, nature these cellulose wood and components lignin are solubleare susceptible only under to microbialrather extreme degradation. chemical conditions,Also, contrary but in natureto Arnold these’s woodviews, components cell wall are constituents susceptible tohave microbial been demonstrateddegradation. Also,to have contrary a strong to affinity Arnold’s for dissolved views, cell silica. wall This constituents process is have now beencommonly demonstrated referred to ashave “organic a strong templating”. affinity for Following dissolved sections silica. Thisof this process paper ispresent now commonly various lines referred of evidence to as “organicrelevant totemplating”. the wood silicification Following sections process. of this paper present various lines of evidence relevant to the wood silicificationIf simple process. permineralization, as envisioned by Arnold, is a valid concept, quantitative analysis of relictIf organic simple permineralization,matter in silicified as wood envisioned should by reveal Arnold, a ishigh a valid percentage concept, of quantitative the original analysis organic of matter.relict organic As a further matter inconfirmation, silicified wood microscopic should reveal exam aination high percentage should show of the the original presence organic of intact matter. cell Aswalls, a further with silica-filled confirmation, cell microscopic lumen and examination intercellular should spaces. show The the permineralization presence of intact model cell walls, also withpresumes silica-filled that the cell first lumen step and in intercellularpetrifaction spaces.is the precipitation The permineralization of silica in model these also voids. presumes Abundant that evidencethe first step exists in to petrifaction show that ismany the precipitationpetrified wood of silicaspecimens in these do voids.not exhibit Abundant these characteristics. evidence exists to show that many petrified wood specimens do not exhibit these characteristics. 3. Organic Templating as First Step in Permineralization Historical interpretations of permineralization assumed that petrifaction occurs when minerals are precipitated in cell lumina and intercellular spaces, entombing intact cell walls. The modern concept of organic templating conflicts with this hypothesis. Experimental studies by Leo and Barghoorn [6], reveal that initial silica deposition begins within cell walls rather than in cell lumina. Their laboratory studies revealed that initial silica precipitation involves the affinity of silicic acid for

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3. Organic Templating as First Step in Permineralization Historical interpretations of permineralization assumed that petrifaction occurs when minerals are precipitated in cell lumina and intercellular spaces, entombing intact cell walls. The modern concept of organic templating conflicts with this hypothesis. Experimental studies by Leo and Barghoorn [6], reveal that initial silica deposition begins within cell walls rather than in cell lumina. Their laboratory studies revealed that initial silica precipitation involves the affinity of silicic acid for hydroxyl groups in hollocelluloses and lignins, the primary structural components of plant vascular tissue. This experimental evidence is in marked contrast to Arnold’s assertion [4] that there is no chemical affinity between silica and organic compounds present in wood. The silicification sequence described by Leo and Barghoorn [6] is the basis for the hypothesis of “organic templating”. Observations of silicified wood provide abundant support for this concept. This discovery has significant relevance for the present study: if cell walls are the initial site for silica deposition, anatomical details may be preserved even though the original organic materials were later lost. In this situation, fossil wood can be considered permineralized during the incipient stages of petrifaction, when silica is infiltrating porous cell walls. However, the final product is typically silicified wood that contains only a very small proportion of the original material. Thus, a fossilization process that began as permineralization ultimately produces a petrifaction that could perhaps more accurately be described as replacement.

4. SEM Evidence During wood petrifaction, where silica precipitation may occur in several stages, with different polymorphs deposited in separate episodes [7–9], these silica minerals may undergo diagenetic transformation, e.g., amorphous opal opal-A transforms to microcrystalline opal-Ct, which may convert to chalcedony. When wood has been fully petrified, mineralization involves all the anatomical features, producing the dense, homogeneous material favored by collectors because the material can be polished to high luster. However, in specimens that contain incomplete mineralization, fractured surfaces may contain open spaces that show the anatomical architecture in three dimensions; these specimens are ideally suited for examination by scanning electron microscopy (SEM). Methods are described in AppendixA. SEM photomicrographs from petrified wood show that mineralization commonly begins with silica deposition in cell walls (Figures2 and3), consistent with the organic templating hypothesis of Leo and Barghoorn [6]. In many silicified wood specimens, cell lumina remain empty, and cell walls show no visible presence of original tissue. In specimens that show deposition of silica within cell lumina (Figure4), this deposition typically occurs after cell walls have already been replaced by earlier mineral polymorphs. Intercellular spaces may remain open even after cell lumina have become mineral-filled (Figure4a,b). In summary, SEM images of silicified wood seldom support the classic permineralization hypothesis, where minerals entomb the original cellular material. Geosciences 2017, 7, 119 5 of 17 Geosciences 2017, 7, 119 5 of 17

Figure 2. Scanning electron microscopy (SEM) images of silicified woods with mineralized cell walls Figure 2. Scanning electron microscopy (SEM) images of siliciﬁed woods with mineralized cell walls and empty lumina (some examples are marked with star symbols). (A) Miocene conifer wood showing and empty lumina (some examples are marked with star symbols). (A) Miocene conifer wood showing a tracheid with opaline walls and botryoidal opal-A layer on interior surface, Lyon County, NV, USA; a tracheid with opaline walls and botryoidal opal-A layer on interior surface, Lyon County, NV, USA; (B) Miocene opalized wood from Lovelock, NV, USA, Radial orientation showing silicified cell walls (B) Miocene opalized wood from Lovelock, NV, USA, Radial orientation showing siliciﬁed cell walls and empty lumina; (C) Miocene wood from Norita Opal Mine, Virgin Valley, NV, USA. Transverse and empty lumina; (C) Miocene wood from Norita Opal Mine, Virgin Valley, NV, USA. Transverse view shows cell walls containing an interior lining of microcrystalline opal-CT; (D) Tertiary opalized viewwood shows from cell Soccorro, walls containingNM, USA. Radial an interior view showing lining of detailed microcrystalline anatomical opal-CT; preservation; (D) Tertiary (E) Transverse opalized woodorientation, from Soccorro, Miocene NM, wood USA. from Radial Cessily view Anne showing Opal Mine, detailed Virgin anatomical Valley, NV, preservation; USA. Opal replacement (E) Transverse orientation,of cell walls Miocene obliterated wood the from original Cessily multi-layere Anne Opald Mine, architecture. Virgin Valley,Lumina NV, are USA. lined Opal with replacement botryoidal of cellopal-A walls and obliterated microcrystalline the original opal-CT; multi-layered (F) Miocene architecture. wood from Lumina Washoe are Co linedunty, withNV, USA, botryoidal transverse opal-A andorientation. microcrystalline Cell walls opal-CT; are replaced (F) Miocene by opal-A, wood with from botryoidal Washoe textures County, on NV, interior USA, surfaces. transverse orientation. Cell walls are replaced by opal-A, with botryoidal textures on interior surfaces.

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Figure 3. SEM images of silicified woods showing cell walls where anatomical features have been Figurereplicated 3. SEM by imagessilica minerals. of siliciﬁed (A) Miocene woods showingwood from cell Schurz, walls NV, where USA, anatomical radial orientation features showing have been replicatedcells walls by replaced silica minerals. by opal-CT; (A) Miocene (B) Miocene wood oak, from Clover Schurz, Creek, NV, ID, USA, USA. radial Radial orientation orientation, showing interior cells wallsview replaced of a tracheid by opal-CT; replaced (B) Miocene by opal-CT; oak, Clover(C) Miocene Creek, ID,wood, USA. Washoe Radial orientation,County, NV, interior USA. viewRadial of a tracheidorientation, replaced tracheid by opal-CT; walls mineralized (C) Miocene with wood, opal-A; Washoe (D) County,Miocene NV,wood USA. from Radial Section orientation, 27 claim, Virgin tracheid wallsValley, mineralized NV, USA, with Cell opal-A; walls show (D) Miocene multi-layered wood architecture, from Section consisting 27 claim, of Virgin porous Valley, opal-A NV, with USA, Cellsurface walls layer show of multi-layered botryoidal opal-A; architecture, (E) Eocene consisting wood from of porous Yellowstone opal-A River, with surface near Billings, layer of MT, botryoidal USA. opal-A;Radial (E )orientation, Eocene wood tracheids from Yellowstone architecture River, mimicked near Billings, by microcrystalline MT, USA. Radial quartz; orientation, (F) Cretaceous tracheids architectureconifer wood, mimicked Trinity by County, microcrystalline TX, USA. quartz; Radial (F )orie Cretaceousntation, tracheids conifer wood, replicated Trinity with County, crystalline TX, USA. Radialquartz. orientation, tracheids replicated with crystalline quartz.

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Figure 4. Mineralized cells, Miocene specimens showing opaline silica filling cell lumina and as a Figure 4. Mineralized cells, Miocene specimens showing opaline silica filling cell lumina and as a replacement for cell walls. (A) Bonanza Opal Mine, Virgin Valley, NV, USA. Transverse orientation, replacement for cell walls. (A) Bonanza Opal Mine, Virgin Valley, NV, USA. Transverse orientation, cell walls and lumina mineralized with opal-CT; (B) Norita Opal Mine, Virgin Valley, NV, USA. cell wallsTransverse and luminaorientation, mineralized cells and lumina with opal-CT;filled with ( Bopal-CT,) Norita intercellular Opal Mine, spaces Virgin remain Valley, open; NV, (C) USA. TransverseWashoe orientation,County, NV, USA, cells oblique and lumina transverse filled orientation, with opal-CT, cell walls intercellular mineralized with spaces opal-A, remain lumen open; (C) Washoefilled with County, porous NV, opal; USA, (D) Washoe oblique County, transverse NV, orientation,USA, oblique cell transverse walls mineralizedorientation, cell with walls opal-A, lumenmineralized filled with with porous opal-A, opal; lumina (D) Washoelined with County, amorphou NV,s USA,porous oblique opal, central transverse area partially orientation, filled with cell walls mineralizedbotryoidal with opal-A; opal-A, (E lumina,F) Hazen, lined NV, with USA, amorphous radial orientatio porousn, opal, cells central mineralized area partially with opal-A filled with botryoidallepispheres. opal-A; These (E,F lepispheres) Hazen, NV, partially USA, fill radial cell lumina, orientation, rather cells than mineralized replicating actual with tissue. opal-A lepispheres. These lepispheres partially fill cell lumina, rather than replicating actual tissue. 5. Effect of Hydrofluoric Acid Treatment 5. Effect ofAs Hydrofluoricnoted in the introduction, Acid Treatment a common assertion has been that hydrofluoric acid treatment of silicified wood dissolves permineralizing silica to reveal original wood cells. The weakness of this Ashypothesis noted inis thethat introduction,prior to the curr aent common study, it assertion had seldom has been been tested. that St. hydrofluoric John [2] reported acid treatmentvariable of silicifiedresults wood from dissolves her HF experiments, permineralizing but the silicafragility to of reveal the relict original tissue wood hinder cells.ed accurate The weakness microscopic of this hypothesisobservations. is that My prior own to experiments the current involved study, it treatment had seldom of silicified been tested. wood St.chips John that [2 were] reported cemented variable resultsto fromaluminum her HF sample experiments, holders, butallowing the fragility SEM images of the to relict be obtained tissue hindered at high accuratemagnification microscopic on observations.HF-treated My specimen own experiments surfaces that involved were treatmentnot damaged of silicifiedby subsequent wood chipshandling. that wereUnder cemented these to aluminumanalytical sample conditions, holders, cell allowing walls were SEM commonly images observed to be obtained to have at been high replaced magnification by silica onminerals, HF-treated specimen surfaces that were not damaged by subsequent handling. Under these analytical conditions, cell walls were commonly observed to have been replaced by silica minerals, with no visible evidence Geosciences 2017, 7, 119 8 of 17

Geosciences 2017, 7, 119 8 of 17 of relict tissue (Figure5). As noted later in this report, amounts of relict organic matter were determined with no visible evidence of relict tissue (Figure 5). As noted later in this report, amounts of relict by a thermal gravimetric method. organic matter were determined by a thermal gravimetric method.

Figure 5. SEM images of Miocene woods after treatment with hydrofluoric acid. Relict tissue was Figure 5. presentSEM during images early ofstages Miocene of mineralization, woods after but 15 secondsno relict oforganic treatment matter withis visible 40% hydrofluoricin these acid.specimens. Relict tissue Thewas end presentresult meets during the early definition stages of of replacement, mineralization, not butpermineralization. no relict organic (A,B matter). is visibleSpecimen in these from specimens. Cedarville, The CA, endUSA. result (A) Radial meets orientation, the definition (B) transverse of replacement, orientation. not permineralization.Cell walls are (A,B).mineralized Specimen fromwith fibrous Cedarville, chalcedony. CA, USA. Lumina (A) Radial contain orientation, subhedral quartz (B) transverse crystals. ( orientation.C,D) radial views Cell walls are mineralizedof single tracheids, with fibrous showing chalcedony. cell walls Luminamineralized contain with subhedral a mosaic of quartz interlocking crystals. microcrystals (C,D) radial of views of singlechalcedony, tracheids, preserving showing intervessel cell walls pit mineralizedarchitecture. Lumina with a mosaicremain empty. of interlocking (C) Saddle microcrystals Mountain, of chalcedony,Grant County, preserving WA, intervessel USA; (D pit) Yakima architecture. Canyon, Lumina Yakima remain County, empty. WA, ( C)USA, Saddle showing Mountain, Grantchalcedony-replaced County, WA, USA; cell (D )walls Yakima with Canyon, discernable Yakima circular County, pits. WA, USA, showing chalcedony-replaced cell walls with discernable circular pits. 6. Analyses of Relict Organic Matter

6. AnalysesA limitation of Relict of Organic St. John’s Matter 1927 study [2] is that using hydrofluoric acid to dissolve a large volume of silicate rock to reveal a small amount of relict cellular matter yields qualitative visual Aimages, limitation but no of quantitative St. John’s 1927 information study [2 ]in is regard that usings to the hydroﬂuoric organic content. acid to Mustoe dissolve [10] a largeused volumean of silicatealternate rock strategy to reveal that a provides small amount semi-quantitative of relict cellular data. In matter this method, yields qualitative a known volume visual images,of but nopowdered quantitative fossil wood information is heated inat 450 regards °C to toburn the away organic relict content.organic matter. Mustoe The [amount10] used of anoriginal alternate strategycarbon that is providesestimated from semi-quantitative the density of nearest data. Inmode thisrn method,relatives, aand known the percentage volume of relict powdered organic fossil woodmatter is heated can be atcalculated 450 ◦C based to burn on the away loss relicton ignition. organic Results matter. for various The amountsilicified wood of original samples carbon are is shown in Table 1. In nearly every case, the percentage of wood remaining after petrifaction is very estimated from the density of nearest modern relatives, and the percentage of relict organic matter small. These data are consistent with a generalized estimate by Leo and Barghoorn [6] that average can be calculated based on the loss on ignition. Results for various siliciﬁed wood samples are shown abundance of organic tissue in petrified wood is on the order of 10% of the original amount. in Table1. In nearly every case, the percentage of wood remaining after petrifaction is very small.

These data are consistent with a generalized estimate by Leo and Barghoorn [6] that average abundance of organic tissue in petriﬁed wood is on the order of 10% of the original amount.

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Table 1. Preservation of relict organic matter in siliciﬁed wood.

Density Estimated Original Calculated % Age Location Genus Mineralogy * % LOI 450◦ ** g/cm3 Density *** Original Wood Devonian Murray, OK Callixylon chalcedony 2.49 0.41 - - Triassic Holbrook, AZ Araucarioxylon chalcedony 2.62 0.19 0.52 0.96 Cretaceous Montague Co., TX Cupressinoxylon quartz 2.53 0.55 0.45 3.09 Eocene Leesville, LA Palmoxylon chalcedony 2.58 0.14 0.56 0.65 Eocene Eden Valley, WY Palmoxylon chalcedony 2.50 1.39 0.56 6.21 Eocene Watertree River, SC Palmoxylon chalcedony 2.32 2.20 0.56 9.11 Oligocene Panama Palmoxylon chalcedony 2.57 1.24 0.56 5.69 Paleocene North Dakota Metasequoia chalcedony 2.60 0.33 0.45 1.91 Oligocene Rapid City, SD Metasequoia chalcedony 2.62 0.27 0.45 1.57 Eocene Florissant, CO Sequoioxylon chalcedony 2.53 0.36 0.45 2.02 Eocene Florissant, CO Sequoioxylon chalcedony 2.41 0.43 0.45 2.30 Eocene Gallatin Co., MT Sequoioxylon quartz 2.48 3.94 0.45 21.71 Miocene Yakima, WA Platanus chalcedony 2.37 0.83 0.56 3.51 Miocene Yakima, WA Ulmus opal-CT 1.95 2.18 0.60 7.09 Miocene Madras, OR Quercinium opal-CT 2.01 2.80 0.74 7.61 Miocene Swartz Canyon, OR Quercinium chalcedony 2.58 0.78 0.74 2.72 Miocene Bliss Co., Idaho Quercinium opal-CT 1.93 1.65 0.74 4.30 Pleistocene Florida Taxodium chalcedony 2.54 0.55 0.48 2.91 Eocene Cache Creek, BC unknown opal-CT 2.07 4.49 0.45 20.65 Miocene Miller Mtn., NV unknown opal-CT 2.07 3.75 0.45 17.25 Miocene Yakima Co., WA Cupressinoxylon opal-CT 1.99 3.28 0.45 14.50 Miocene Washoe County, NV unknown opal-CT 1.86 2.77 0.45 11.45 Miocene Rawhide, NV unknown opal-CT 1.85 4.68 0.45 19.24 Miocene Lake Tahoe, CA unknown opal-CT 1.90 3.25 0.45 13.72 Neogene Columbia unknown opal-CT 1.90 2.66 0.45 11.23 Miocene Nye County, NV conifer opal-CT 1.90 1.61 0.45 6.80 * Mineralogy determined by X-ray diffraction and scanning electron microscopy; ** Loss on ignition after heating at 450 ◦C; *** Density estimated from extant relatives.

7. Examples of Permineralization Data presented in the preceding section of this report confirms that siliceous petrified woods commonly preserve details of cellular anatomy even though only scant amounts of relict organic matter remain, contrary to the permineralization hypothesis. However, true permineralization can be observed in plant materials that were mineralized in several different geologic environments, e.g., “coal balls” and other calcareous concretions, silicified chert, modern siliceous hot spring sinter, and laboratory simulations.

7.1. Calcareous Mineralizaton, Including Coal Balls First described in 1855 [11], coal balls are calcareous concretions that widely occur in Carboniferous coal beds. A summary of the extensive literature can be found in [12]. Preservation of plant remains is variable, but many specimens show excellent anatomical detail. The common method of study involves treating a flat surface of the concretion with 5% HCl to expose cellular tissue, which is then replicated as an impression made when a thin sheet of cellulose acetate is pressed to the surface after it has been moistened with a solvent (Figure6). Coal balls may provide clues for understanding petrifaction of woods where calcite is the principal mineral constituent. Other calcified wood specimens have been observed to yield acetate peels that show anatomical detail (Figures6–8). Precipitation of calcium carbonate requires geochemical conditions that are very different from the conditions that favor silica precipitation, so inferences drawn from coal balls are not necessarily relevant for interpreting the origin of most petrified wood. The above examples are evidence that calcareous mineralization may preserve large amounts of original tissue, consistent with the permineralization concept. However, in some deposits wood mineralized with calcium carbonate may contain only small amounts of organic matter (Figure8). This variation suggests that the organic matter: calcium carbonate ratio reflects the rate of mineralization versus the rate of tissue degradation, the same phenomenon that occurs during wood silicification. Geosciences 2017, 7, 119 10 of 17 Geosciences 2017, 7, 119 10 of 17

The above examples are evidence that calcareous mineralization may preserve large amounts of original tissue, consistent with the permineralization concept. However, in some deposits wood mineralized with calcium carbonate may contain only small amounts of organic matter (Figure 8). This variation suggests that the organic matter: calcium carbonate ratio reflects the rate of Geosciencesmineralization2017, 7, 119versus the rate of tissue degradation, the same phenomenon that occurs during 10wood of 17 silicification.

Figure 6. Woods permineralized with calcite. (A–C) acetate peels of teredo-bored wood in a Figure 6. Woods permineralized with calcite. (A–C) acetate peels of teredo-bored wood in a calcareous calcareous concretion, Lower Cretaceous, Apple Bay, Vancouver Island, BC, Canada; (D) concretion, Lower Cretaceous, Apple Bay, Vancouver Island, BC, Canada; (D) Longitudinal section of Longitudinal section of apical region of ovulate cone of Hubbardiastrobus cunninghamiodes from Apple apical region of ovulate cone of Hubbardiastrobus cunninghamiodes from Apple Bay [13] (photo courtesy Bay [13] (photo courtesy of Brian A. Atkinson; (E) Calamites stem in Pennsylvanian coal ball, of Brian A. Atkinson; (E) Calamites stem in Pennsylvanian coal ball, Lancashire coal ﬁeld, England. Lancashire coal field, England. Photo courtesy of Hans Steur; (F) Anacheropteris involuta preserved in Photo courtesy of Hans Steur; (F) Anacheropteris involuta preserved in Upper Pennsylvanian coal ball, Upper Pennsylvanian coal ball, IL, USA. Photo courtesy of University of Mūnster Paleobotany IL, USA. Photo courtesy of University of Munster¯ Paleobotany Research Center. Research Center.

Figure 7. Permineralization: cell walls of Lower Jurassic fern Osmundastrum pulchellum from Figure 7.7. Permineralization:Permineralization: cell cell walls walls of of Lower Lower Jurassic fern Osmundastrum pulchellum fromfrom Korsarőd, Sweden, revealed by HCl dissolution of calcareous matrix to reveal original cell walls [14]. Korsar˝od,Sweden,Korsarőd, Sweden, revealed by HCl dissolution of calcareo calcareousus matrix to reveal original cell walls [14]. [14]. Photo courtesy of Stephen McLoughlin. Photo courtesy of StephenStephen McLoughlin.McLoughlin.

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Figure 8. Calcite-mineralized woods showing weak or no evidence of permineralization. (A–E) are Figurefrom 8. Calcite-mineralized the Cretaceous Nanaimo woods Group, showing Vancouver weak Island, or no evidence BC, Canada. of permineralization. (A) Specimen from (PuntledgeA–E) are from the CretaceousRiver, transverse Nanaimo orientation. Group, Relict Vancouver organic Island, matter BC,is present Canada. as very (A) thin Specimen cell borders; from ( PuntledgeB) Specimen River, transversefrom Collishaw orientation. Point, Relict Hornby organic Island, matter transverse is present orientation. as very Relict thin organic cell borders; matter causes (B) Specimen thin walls from Collishawto be brownish Point, Hornby red; (C Island,) SEM view transverse of a single orientation. tracheid of Relict Puntledge organic River matter wood. causes Cell wall thin appears wallsto be brownishthick red;because (C) of SEM microcrystalline view of a single calcite. tracheid Lumen ofis filled Puntledge with more River coarsely wood. crystalline Cell wall calcite; appears (D) thick becauseSEM of view, microcrystalline specimen from calcite. Port Moody, Lumen tangential is filled with orientation. more coarsely Relict smooth crystalline surfaces calcite; of cell ( Dwalls) SEM are view, specimenmineralized from Port with Moody, calcite; tangential (E) Port orientation. Hardy specimen, Relict smooth transverse surfaces orientation. of cell walls Polarized are mineralized light illumination shows radiating calcite crystals that have disrupted cellular tissue; preserve smooth with calcite; (E) Port Hardy specimen, transverse orientation. Polarized light illumination shows texture; (F) Neogene wood from Glades County, FL, USA. Tangential orientation, showing tracheid radiating calcite crystals that have disrupted cellular tissue; preserve smooth texture; (F) Neogene walls mineralized with coarsely-crystalline calcite. wood from Glades County, FL, USA. Tangential orientation, showing tracheid walls mineralized with coarsely-crystalline7.2. Siliceous Lagerstätten calcite. Silica precipitated in peat bogs may entomb plant remains, providing examples of true 7.2. Siliceous Lagerstätten permineralization. Two of the best-known examples are the Devonian Rhynie Chert in Scotland, and Silicathe Eocene precipitated Princeton inChert peat in bogsBritishmay Columbia, entomb Canada. plant At remains, both localities, providing fossilization examples involved of true permineralization.silicification of ancient Two of peat the bo best-knowngs, but geochemical examples conditions are the at Devonian the two sites Rhynie were Chertvery different. in Scotland, and theThe Eocene Rhynie Princeton Chert involved Chert silica in British precipitation Columbia, in a Canada.hot spring At environmen both localities,t [15–17]. fossilization The Princeton involved Chert has been interpreted to result from cyclic fluvial processes that ensued from episodes of silicification of ancient peat bogs, but geochemical conditions at the two sites were very different. The Rhynie Chert involved silica precipitation in a hot spring environment [15–17]. The Princeton Chert has been interpreted to result from cyclic fluvial processes that ensued from episodes of tectonic Geosciences 2017, 7, 119 12 of 17 Geosciences 2017,, 7,, 119119 12 of 17 tectonictilting of tilting a floodplain of a floodplain [18]. At both[18]. localities,At both locali plantties, tissues plant are tissues preserved are pres inerved exquisite in exquisite detail, Cellular detail, Cellulararchitecture architecture can be revealed can be usingrevealed the using acetate the peel acet method,ate peel using method, hydrofluoric using hydrofluoric acid to etch acid the surfaceto etch theof chert surface slabs, of evidencechert slabs, of the evidence existence of ofthe permineralized existence of permineralized tissue. Fossilized tissue. tissues Fossilized include foliage,tissues includesteminclude tissue foliage,foliage, (Figure stemstem9), tissuetissue seeds, (Figure(Figure and fruit, 9),9), butseedseed petrifieds, and fruit, wood but is petr scarce.ifiedified woodwood isis scarce.scarce.

Figure 9. SiliceousSiliceous permineralizationpermineralization asas revealed in acetate peels. A. Rhynia Gwynne-vaughanii,, Figure 9. Siliceous permineralization as revealed in acetate peels. A. Rhynia Gwynne-vaughanii, transversetransverse viewview ofof stem,stem, Devonian,Devonian, RhynieRhynie chert,chert, ScotlandScotland [19,20].[19,20]. PhotoPhoto courtesycourtesy ofof PaleobotanyPaleobotany transverse view of stem, Devonian, Rhynie chert, Scotland [19,20]. Photo courtesy of Paleobotany Research Center University of Münster; B. Millerocaulis zammerae,, transversetransverse viewview ofof stem,stem, Jurassic,Jurassic, Research Center University of Münster; B. Millerocaulis zammerae, transverse view of stem, Jurassic, Patagonia, Argentina [21]. Photo courtesy of Ana Sagasti). Patagonia, Argentina [21]. Photo courtesy of Ana Sagasti).

Conifer wood in the Lower Eocene lignite beds in Mississippi, USA provides an unusual exampleConifer of permineralization. wood in the Lower EoceneThis site lignite contains beds inwood Mississippi, that is USAmostly provides mummified an unusual (i.e., exampleoriginal tissue),of permineralization. with small amounts This site of contains silica (Figure wood 10), that as is mostlywell as mummified petrified specimens (i.e., original that tissue), have silica-filled with small luminaamountslumina (Figure(Figure of silica 11).11). (Figure TheseThese 10 specimensspecimens), as well as areare petrified examplesexamples specimens of permineralization, that have silica-filled where lumina original (Figure cells are11). preservedThese specimens are examples of permineralization, where original cells are preserved

Figure 10. EoceneEocene coniferconifer woodwood fromfrom RedRed HillsHills LigniteLignite Mine,Mine, ChoctawChoctaw County,County, AL,AL, USA.USA. ((A)) Figure 10. Eocene conifer wood from Red Hills Lignite Mine, Choctaw County, AL, USA. Mummified wood, oblique transverse orientation, showing preservation of multi-layered cell walls; (A) Mummiﬁed wood, oblique transverse orientation, showing preservation of multi-layered cell ((B)) PartiallyPartially silicifiedsilicified wood,wood, tangentialtangential orientation,orientation, showingshowing lace-likelace-like degradationdegradation ofof cellcell wall,wall, andand SiSi walls; (B) Partially siliciﬁed wood, tangential orientation, showing lace-like degradation of cell wall, precipitation in f outer wall (arrow). and Si precipitation in f outer wall (arrow).

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Figure 11. Permineralized Lower Eocene conifer wood, Red Hills Lignite Mine, Choctaw County, Figure 11. Permineralized Lower Eocene conifer wood, Red Hills Lignite Mine, Choctaw County, MS, USA. (A,B) Transverse orientation, showing organic mummified cell walls with lumina and MS, USA. (A,B) Transverse orientation, showing organic mummified cell walls with lumina and intercellular space filled with silica. intercellular space filled with silica. 7.3. Modern Hot Springs 7.3. Modern Hot Springs Hot springs that produce siliceous sinter may cause wood to become encrusted and infiltrated Hot springs that produce siliceous sinter may cause wood to become encrusted and infiltrated with with amorphous opal. Examples include logs, limbs and other plant materials that are transported amorphous opal. Examples include logs, limbs and other plant materials that are transported into the into the hot spring by wind or gravity, but silica deposition may also occur in trunks of living trees hot spring by wind or gravity, but silica deposition may also occur in trunks of living trees that inhabit that inhabit the geothermal area. Dissolved silica concentrations may be very high in hot spring water, the geothermal area. Dissolved silica concentrations may be very high in hot spring water, and silica and silica precipitation rates may be very rapid. For example, at the sinter apron bordering Cistern precipitation rates may be very rapid. For example, at the sinter apron bordering Cistern Spring in Spring in Yellowstone National Park, USA, silica is deposited at a rate of ~5 cm/year [22]. Windfall Yellowstone National Park, USA, silica is deposited at a rate of ~5 cm/year [22]. Windfall causes trunks causes trunks and branches of Lodgepole Pine (Pinus contorta) to be abundant at Cistern Spring, and and branches of Lodgepole Pine (Pinus contorta) to be abundant at Cistern Spring, and this wood this wood undergoes rapid silicification [23]. Similar wood occurs at many Yellowstone hot springs undergoes rapid silicification [23]. Similar wood occurs at many Yellowstone hot springs (Figure 12). (Figure 12). At another site, silica deposition on wood was reported as 0.1–4.0 mm/year [24]. Rapid Atsilicification another site, of silicamodern deposition wood onhas wood also was been reported reported as 0.1–4.0 from mm/year hot springs [24]. Rapidin Japan silicification [25,26]. ofIn modernaddition woodto natural has alsooccurrences, been reported several from researchers hot springs havein placed Japan wood [25,26 samples]. In addition in hot tosprings natural to occurrences,observe the process several of researchers rapid silicification have placed [26,27]. wood samples in hot springs to observe the process of rapidConsideration silicification [ 26of, 27hot]. springs for fossilization of wood has an important caveat. Hot spring sinterConsideration aprons are characterized of hot springs by for rapid fossilization silica precipitation of wood has anthat important may result caveat. in encrustation Hot spring sinter and apronsincipient are permineralization characterized by of rapid wood, silica but precipitation these deposits that are may not result good inanalogs encrustation for the andformation incipient of permineralizationpetrified wood. The of wood, reason but is thesethat depositsthe hydrothermal are not good environments analogs for theare formation either strongly of petrified oxidizing, wood. Thewith reason pH that is thatis either the hydrothermal very high (alkaline environments chloride are hot either springs), strongly or strongly oxidizing, reducing, with pH with that very is either low verypH (acid high sulfide (alkaline hot chloride springs). hot In these springs), harsh or enviro stronglynments, reducing, organic with matter very is low rapidly pH (acid destroyed. sulfide As hot a springs).result, twigs In these or woody harsh environments,debris falling into organic the matterspring ismay rapidly initially destroyed. become As encrusted a result, twigs and infiltrated or woody debriswith silica, falling but into silicified the spring wood may is seldom initially preserved become encrusted as the sinter and ages. infiltrated Plant fossils with silica, are most but silicifiedlikely to woodbe preserved is seldom only preserved as casts asor themold sinters rather ages. than Plant mineralized fossils are tissues. most likely to be preserved only as casts or molds rather than mineralized tissues.

Geosciences 2017, 7, 119 14 of 17 Geosciences 2017, 7, 119 14 of 17

Figure 12. Incipient permineralization of modern Pinus contorta (Lodgepole Pine) wood can be Figure 12. Incipient permineralization of modern Pinus contorta (Lodgepole Pine) wood can be observed observed at hot springs in Yellowstone Park, WY, USA. (A,B) silica encrusted woody debris on hot at hot springs in Yellowstone Park, WY, USA. (A,B) silica encrusted woody debris on hot spring sinter spring sinter apron; (C) Distribution of silica as mapped by X-ray microanalysis of transverse apron;specimen. (C) Distribution Warm, bright of silica colors as mapped represent by areas X-ray of microanalysiselevated silica. ofIncipient transverse silcification specimen. has Warm,occurred bright colorsnear represent exterior areas surfaces of elevatedand along silica. fractures Incipient [23]; (D silciﬁcation) Radial orientation, has occurred showing near cells exterior encrusted surfaces with and alongamorphous fractures [silica23]; ( D(opal-A);) Radial (E orientation,) Transverse view, showing tracheids cells encrustedshowing multilayered with amorphous unmineralized silica (opal-A); cell (E) Transversewalls, with view, opal-A tracheids precipitated showing on interior multilayered surfaces; unmineralized (F) High magnification cell walls, shows with opal-Athin silica precipitated zone on interior(arrow) surfaces; as an interlayer (F) High within magniﬁcation tracheid cell shows walls; thin(G) Opal-A silica zone lepispheres (arrow) encrust as an a interlayer pit aperture within tracheidplate. cell walls; (G) Opal-A lepispheres encrust a pit aperture plate.

7.4. Laboratory7.4. Laboratory Simulations Simulations Recipes for rapid wood petrifaction date to 16th century alchemists; more than 500 years later Recipes for rapid wood petrifaction date to 16th century alchemists; more than 500 years later researchers are still perfecting methods for “turning wood to stone”. A comprehensive overview of researchersthese experiments are still perfecting appears in methods a recent article for “turning [28]. Several wood basic to strategies stone”. Ahave comprehensive been employed, overview the of thesesimplest experiments approach appears being to in infiltrate a recent silica-bea article [ring28]. solutions Several basicinto permeable strategies wood, have beenoften employed,using the simplestelevated approachtemperatures being to tospeed inﬁltrate the rate silica-bearing of silica precipitation. solutions into The permeable result is wood,wood oftenthat is using elevatedpermineralized, temperatures retaining to speed virtually the rate all of of silica the original precipitation. cellular tissue. The result A modification is wood that of this is permineralized, method is retainingto use virtually boiling water all of or the chemical original solvents cellular to tissue. remove A low-molecular modiﬁcation weight of this components, method is toleaving use boiling a waterlignin/cellulose or chemical solvents framework to remove[6,29]. At low-molecular the completion of weight silica deposition, components, organic leaving matter a lignin/cellulose is removed frameworkby wet-ashing [6,29]. with At the strong completion mineral acids, of silica or high deposition, temperature organic combustion. matter A is modern removed trend by has wet-ashing been with strong mineral acids, or high temperature combustion. A modern trend has been to use wood as a template for deposition of ceramic materials such as silicon carbide [28–31], or zeolites [32]. The goal of these studies has been to achieve porous materials that have industrial value, rather than to duplicate Geosciences 2017, 7, 119 15 of 17

Geosciencesto use 2017wood, 7, 119as a template for deposition of ceramic materials such as silicon carbide [28–31],15 or of 17 zeolites [32]. The goal of these studies has been to achieve porous materials that have industrial value, rather than to duplicate natural silicification. Despite these experimental variations, the initial natural siliciﬁcation. Despite these experimental variations, the initial steps in these processes all steps in these processes all involve permineralization, where silica precipitates in open spaces within involvethe intact permineralization, wood (Figure 13). where silica precipitates in open spaces within the intact wood (Figure 13).

Figure 13. Experimental silica permineralization of modern conifer wood, Pseudotsuga menziesii. Figure 13. Experimental silica permineralization of modern conifer wood, Pseudotsuga menziesii. Samples were exposed to H4SiO4 saturated solutions for ~90 days at 90 °C, with obsidian powder as the Samples were exposed to H SiO saturated solutions for ~90 days at 90 ◦C, with obsidian powder silica source [33]. (A) Transverse4 4 orientation, showing tracheid lumina filled with silica gel aggregate; as the silica source [33]. (A) Transverse orientation, showing tracheid lumina filled with silica gel (B) reflected light image of a longitudinal section cut parallel to the tracheids using a scalpel, showing aggregate; (B) reflected light image of a longitudinal section cut parallel to the tracheids using a scalpel, lumina permineralized with silica gel. Photos courtesy of Chris Ballhaus, Bonn University. showing lumina permineralized with silica gel. Photos courtesy of Chris Ballhaus, Bonn University. 8. Discussion 8. Discussion Examples of wood petrifaction can be found that neatly fall into categories of permineralization andExamples replacement of, wood but more petrifaction commonly can fossil be found wood that results neatly from fall intoa combination categories of permineralizationthese processes. andInfiltrationreplacement of ,mineral-bearing but more commonly groundwater fossil may wood initially results cause from permineralization a combination of of cellular these processes.tissues, Infiltrationbut the wood of mineral-bearing is also undergoing groundwater gradual degradat may initiallyion. Thus, cause wood permineralization petrifaction commonly of cellular involves tissues, butsimultaneous the wood is alsodegradation undergoing and gradual mineralization. degradation. Permineralization Thus, wood petrifaction and replacement commonly are involves not simultaneousindependent degradation processes; andinstead, mineralization. they commonly Permineralization occur concurrently. and replacement The fidelity are notof anatomical independent processes;preservation instead, depends they commonly on the relative occur rates concurrently. of these Theprocesses. fidelity Rapid of anatomical rates of preservationmineral deposition depends onunder the relative relatively rates mild of these Eh processes.and pH conditions Rapid rates fa ofvor mineral the preservation deposition underof organic relatively matter. mild These Eh and pHconditions conditions appear favor theto be preservation more common of organic for calcium matter. carbonate These conditions deposition appear than for to besilicification, more common as forevidenced calcium carbonate by observations deposition of permineraliz than for silicification,ed wood specimens as evidenced from by many observations localities. of permineralized SEM images and HF etched specimens show silicification commonly begins at cell walls, but wood specimens from many localities. subsequent mineralization may occur via multiple pathways [7–9,34,35]. The preservation of relict SEM images and HF etched specimens show silicification commonly begins at cell walls, organic matter is highly variable, but commonly very low. Because of these complexities, as general but subsequent mineralization may occur via multiple pathways [7–9,34,35]. The preservation of relict descriptive terms, “mineralization” and “mineralized” are more accurate than “permineralization” organic matter is highly variable, but commonly very low. Because of these complexities, as general and “permineralized”. descriptive terms, “mineralization” and “mineralized” are more accurate than “permineralization” andAcknowledgments: “permineralized”. I thank Graham Beard for providing specimens and acetate peels for Vancouver Island, BC, Canada fossil wood, David Lang for allowing me to study Eocene wood from his study site in Mississippi, USA. Acknowledgments:Other specimens wereI thank contributed Graham by Beard Les & forGeri providing Maxwell, Jim specimens Mills, and and John acetate Church peels. Photos for were Vancouver generously Island, BC,provided Canada by fossil Brian wood, Atkinson, David Chris Lang Ballhaus, for allowing Stephen me McLoughlin, to study Eocene Ana woodSagasti, from and hisHans study Steur. site in Mississippi, USA. Other specimens were contributed by Les & Geri Maxwell, Jim Mills, and John Church. Photos were generouslyConflicts provided of Interest: by The Brian author Atkinson, declares Chris no conflict Ballhaus, of interest. Stephen McLoughlin, Ana Sagasti, and Hans Steur. Conflicts of Interest: The author declares no conflict of interest. Appendix A. Analytical Methods AppendixElectron A. Analytical photomicrographs Methods were made using a VEGA Tescan scanning electron microscope (www.tescan-usa.com),Electron photomicrographs with specimens were made mounted using on a VEGAaluminum Tescan stubs scanning with epoxy electron adhesive microscope and (www.tescan-usa.comsputter coated with), Au. with Optical specimens photomicrograp mounted onhs aluminum were obtained stubs with using epoxy a 1960s adhesive vintage and Zeiss sputter coatedpetrographic with Au. microscope Optical photomicrographs equipped with werean in obtainedexpensive using Cnscope a 1960s 5 megapixel vintage Zeiss CMOS petrographic digital microscopemicroscope equipped camera with(http://store an inexpensives.ebay.com/globalseller25?_trksi Cnscope 5 megapixeld=p2047675.l2563). CMOS digital microscope Images camerawere (http://stores.ebay.com/globalseller25?_trksid=p2047675.l2563 ). Images were captured via USB connection using Amcap software; scale bars for optical and SEM photomicrographs were added using Adobe Illustrator. Quantitative thermal gravimetric methods were described in detail in a previous Geosciences 2017, 7, 119 16 of 17 publication [10]. Mineral compositions of specimens shown in Figures2–12 were determined by Energy Dispersive Spectroscopy (EDS) analysis for SEM specimens, and by polarized light microscopy for thin sections. In most instances, the composition of bulk specimens used to prepare microscope samples were first verified using X-ray diffraction (Rigaku Geigerflex diffactometer using Ni-filtered K-α radiation). Specimens used in this investigation are archived in the author’s research collection at Western Washington University, Bellingham, WA, USA.

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