Copyright © 1980 Ohio Acad. Sci. 0030-0950/80/0001-002012.00/0

DESCRIPTIVE MINERALOGY OF PUGH QUARRY,NORTHWESTERN OHIO: BARITE AND CELESTITE1

DAVID F. PARR2 and LUKE L. Y. CHANG, Department of Geology, Miami University, Oxford,OH 45056

Abstract. Two sulfate minerals, barite and celestite, were identified in the Devonianrocks at Pugh Quarry. The barite occurs commonly as rosette-like clusters with widevariety of colors and crystal habits. Unusual features include paired crystals andhollow crystals. The former consist of two barite crystals growing parallel with eachother on the dolostone matrix, and the latter only of a thin wall of barite commonlymarked by cross striations. Celestite crystals have two different colors. The gray-blue and blue crystals are prismatic to blocky and occur as well-formed individuals,whereas the colorless and white crystals are tabular to bladed and occur as distinctindividuals and as compact clusters.

OHIO J. SCI. 80(1): 20, 1980

This is the fourth and last part of themineralogy studies of Pugh Quarry. Thequarry is located in the SW>2, SW34,Sec. 6, T.4N, R.9E in Milton Township,Wood Co., Ohio, and has quite a diversi-fied mineral assemblage. In addition tothe barite and celstite described in thispaper, there are the sulfides: marcasite,pyrite, and sphalerite (Parr and Chang1977, 1978), the carbonates: calcite anddolomite (Parr and Chang 1979), andfluorite (Parr and Chang, 1979).

BARITEBarite is far less common than calcite

at Pugh Quarry. It is most abundantin the mineral zone (Parr and Chang1977) and also occurs less abundantly inisolated cavities stratigraphically lowerthan the mineral zone. The highestconcentrations of this mineral are in theeastern portion of the north wall of thequarry.

Relation to Host Rock. Most thin-sections revealed a thin zone of calcite,2 to 3 mm thick, separating the baritefrom host rock (fig. 1). The calcite zoneconsists of crystals of the "small type"(Parr and Chang 1979), and calciteterminations project into the basal por-

^anuscript received 8 November 1978(#78-66).

2Present Address: Department of Geology,Wisconsin State Univ., Superior, Wisconsin54880.

FIGURE 1. Thin section, crossed nicols. Bariteon small calcite on dolostone. Note euhedralsmall calcite crystals forming a separatinglayer between the barite (right) and the dolo-stone (left). (X25)

tion of the encrusting barite. Rarelythe barite can be seen to be intergrownwith these small calcite crystals.

In other specimens, barite was found

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to form directly on dolostone, but noevidence indicates the replacement ofdolostone by barite. Some dolostonerhombs are enclosed in barite near thedolostone-barite interface (fig. 2). These

FIGURE 2. Thin section, crossed nicols. Ba-rite on dolostone. Note sharp dolomiterhombs enclosed in the barite. (X25)

rhombs have sharp borders and areseveral times larger than the rhombscomposing the dolostone matrix. Theselarge dolostone rhombs may have formedcontemporaneously with the barite en-closing them.

Color and Size. The barite found atPugh Quarry occurs in a wide varietyof colors: colorless, cream, cream-white,white, pale blue, blue-gray, blue-green,green-yellow, and yellow-brown. Morethan one color can be observed as zoneswithin a single crystal or cluster ofcrystals. Commonly, the barite is cream,white, or pale blue. All barite from thequarry is translucent, and many speci-mens are transparent near the thin edgesof the crystals. Luster of the crystalsand crystal aggregates is generally fromglossy to pearly and less commonly dullto earthy.

Barite rarely occurs as individualcrystals in Pugh Quarry. Most commonare rosette-like clusters of parallel andsub-parallel crystals. These clustersrange from a few millimeters to as muchas 7 centimeters in maximum dimension.Encrustations as much as 5 mm thickand blocky to tabular aggregates werealso found. Diameters of the relativelyrare single crystals range from less than1 mm to more than 2 cm.

Habit and Form. The crystal habits ofthe barite from Pugh Quarry are ex-tremely varied. Crystal aggregates,characterized by curved surfaces, are pre-valent, and their crystal surfaces are ir-regular with vicinal faces commonly visi-ble. These crystal aggregates wereformed by parallel, sub-parallel, split-sheath, and step-growth of a small num-ber of common barite forms (figs. 3 and 4)that were defined on the basis of theirrelation to cleavage planes and approxi-mate measurements made with a contactgoniometer. Invariably, {001} and {210}are present with the modifying forms{010} and {100} occurring rarely. Thecurvature of the crystal faces and themultiplicity of the crystal clusters pre-cluded the use of the optical goniometerin making interfacial angle measurements.

The basic habit of Pugh Quarry bariteis the tabular to plate-like rhombicprism. These rhombic units were rarelyfound separately, but rather combinedtogether to form paired crystals, oblongfourlings, rosettes, spike clusters, crestedaggregates, and layer-and-spike aggre-gates. Barite also occured as so-calledhollow crystals.

Paired crystals consist of two baritecrystals growing parallel with each otheron the dolostone matrix (fig. 5). Thetwo crystals are connected by a barelyvisible coating of barite on the dolostone.This film of connecting material is presenton the matrix only in the small spacebetween the two crystals. Differentgenerations of mineral growth are dis-cernable as zones of white barite sand-wiched between two layers of clearbarite, which consist of many wedge-shaped crystal terminations arranged inan imbricate or step-like structure. Themultiple terminations are all part of asingle crystal unit (fig. 5). It is apparent

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FIGURE 3. Barite crystal aggregates. Note split sheath and parallel-subparallel growth of ag-gregates. Cross-section shape of aggregates is rhombic. (X 3.3)FIGURE 4. Barite on dolostone. Parallel and sub-parallel step growth is clearly visible on thesecompound crystals. Note rhombic character of individual crystal units making up larger clusters.Individual rhombic crystals are arranged in a manner giving cluster curved surfaces resemblingsaddle crystals of dolomite. (X 3)FIGURE 5. Barite and small calcite on dolostone. Paired barite crystals. Note the parallelismof each pair, the zone of clear barite, and the imbricate or step-like arrangement of the bariteterminations. (X 8)FIGURE 6. Barite on marcasite. Note the characteristic central opening in the clusters, thevariety of shapes, and the varying stages of development. (X 4)FIGURE 7. Barite crystal aggregates. Composed of a basic unit, the rhombic prism, these rosetteclusters are common in Pugh Quarry. (X 1.5)

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from the parallel arrangement of the twoindividuals constituting the pair that theyare oriented to the same axial system.

The origin of the paired crystals is notcompletely understood. Two hypotheti-cal explanations are presented. The firstinvolves three steps: growth, resorption,and growth. During the first stage, abarite crystal developed that encom-passed an area equal to that presentlyoccupied by the crystal pairs. A changein the solution chemistry then causedmuch of this crystal to be dissolved. Thebarite that was not taken into solutionconsisted of the white material now sand-wiched between the two clear baritelayers. During the third stage, clearbarite was deposited on the remainingportions of the original crystal, the whitematerial. The remnants of the originalcrystal provided the similarly orientedseed crystals on which the clear baritewas formed producing parallel pairedcrystals. The sharp crystal terminationprecludes the possibility that the pairedcrystals are remnants of larger crystals,which have been partially dissolved away.The second is that the paired crystals aresimply a phenomenon of growth. Theparallelism of the paired crystals may beexplained by the connecting layer ofbarite on the matrix between the crystals.This layer carried the crystallographicorientation code by which the two crys-tals developed.

Barite crystal clusters consisting of 4individual lens-shaped aggregates of sub-parallel crystals arranged to form a habitresembling short, flattened tubes wereobserved (fig. 6). These fourling clustersare less than 1 cm in maximum dimension.The arrangement of the 4 individual ag-gregates resulted in an opening in themiddle of the cluster. The 4 componentclusters may be nearly separate from oneanother or they may merge togethermaking the separate character of the indi-vidual units minimal. The nature of thisrelationship is not understood, but num-erous specimens show fourling, lens-shaped clusters, suggesting that coinci-dence is not a valid explanation.

Rosettes as much as 1 cm in diameterare one of the more common barite habitsfound in Pugh Quarry (fig. 7). Thesedo not resemble the classic barite rose

sand crystals from near Norman, Okla-homa. The rosette crystal clusters, gen-erally creamy white, are formed by splitcrystal growth, yielding clusters of curvedcrystals which fan out towards the mar-gins of the clusters. Along the clustermargins, the area of maximum spread,the rosette appears to be composed ofnumerous individual crystals that tapertoward the cluster center.

Some of the individual crystal clustercomposing the rosettes have a distinctsheath-like appearance, whereas othersshow curvature resembling the classicdolomite saddle crystals (fig. 4). Closeexamination of the rosettes reveals thatthe rhombic prism is the pervasive formof the individual platelets in the clusters.Commonly, the rosette clusters exhibit acrude rhombic outline. There is no in-dication that these crystal clusters areanything but the result of primary crystalgrowth.

One of the more unusual barite habitsfound at Pugh Quarry are spike clusterswith length ranges from about 1 cm to5 cm (fig. 8). Numerous small rhombicprisms apparently were the buildingblocks of the larger more complex spike-like clusters. The arrangement of theseprisms in parallel and sub-parallel growthgives many of the elongated spike clustersa Christmas Tree appearance (fig. 9).Commonly, the spikes are bounded bynumerous terminations of the rhombicprisms arranged in an imbricate manner.Sharp, chisel-edged terminations com-monly form the apices of the spike-likecluster (fig. 10). Other spike clustersbranch into many smaller spikes, eachwith its own chisel-edged terminations,giving some specimens a delicate leafyappearance resembling the leaf portionof pineapples. Some spike-like clustersproduce a cockcomb or crested appear-ance at the terminations of the cluster.These terminations are not restricted tothe spike clusters, but are commonlyfound on other types of barite clusters.

The layer-and-spike aggregate habit isshown in fig. 11. Both the layers andthe separating spikes are clusters ofsmaller crystals and the rhombic prismis the basic crystal form. These spikesmay branch in much the same way thatthe larger spike structures do. This

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FIGURE 8.SpecimensFIGURE 9.(X 3.5)FIGURE 10.(X5)FIGURE 11.

Barite. Cluster of barite crystals composed of many smaller spike-like barite clusters,of this type have a delicate leafy overall appearance. (X 1.2)Barite. Spike-like compound crystal cluster with a rough Christmas Tree appearance.

Barite. Spike-like clusters showing the sharp chisel edge terminations of the clusters.

Barite. Note the spike-like character of the clusters that separate the layers of barite.

habit may have resulted from slightperiodic variations in the levels of thesolutions from which precipitation tookplace, and the separating spikes mayhave developed during periods of chang-ing solution levels.

The most unusual habit in which PughQuarry barite was found can best be

described as hollow crystals (figs. 12 and13). These crystals, all of which arewhite, range in size from 0.5 mm wideand 2 mm long to 3 mm wide and 8 mmlong. Cross sections of the crystals aresquare to slightly rectangular and longi-tudinal sections vary from canoe-shapedto rectangular. The hollow crystals con-

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FIGURE 12. Barite hollow crystals and small calcite crystals on dolostone. Note delicate needles of barite extending betweenopposing walls of barite in place of a solid wall. (X 8.2)

FIGURE 13. Barite hollow crystals and small calcite crystals on dolostone. The impingement of calcite crystals into walls ofbarite and the protrustion of the calcite through the barite walls is indicated by arrows. (X 7)

FIGURE 14. Barite hollow crystal and small calcite crystals on dolostone. Note barite needles enclosed in a small calcite crystal(X9)

FIGURE 15. Barite on large calcite. Note heavy accumulations of barite on interfacial joins of the calcite crystal. (X 1.3)

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sist only of thin walls of barite commonlymarked by cross striations. Many indi-viduals appear to be well-formed, solidcrystals, but the thin walls were easilybroken revealing hollow interiors. Manyindividuals showed one or more of thewalls to be incomplete, but with fineneedles of barite commonly extendingacross the hollow crystals in place of awell-formed wall (figs. 12 and 13). Simi-lar delicate barite needles were observedto protude from the walls into the openhollow of the crystals.

The relation between small calcitecrystals and hollow barite crystals iscomplex; well-formed small calcite crys-tals are commonly found inside thehollow barite crystals (fig. 13). Smallcalcite crystals are attached to matrix inthe usual manner and commonly projectthrough the walls of the hollow baritecrystals with part of the calcite crystalinside the hollow barite crystal, and partoutside (fig. 14). In these specimens, thewalls of the hollow crystals can be seento extend partially into the calcite crys-tal, suggesting simultaneous precipitationof the two minerals. The sharp, cleanappearance of the calcite indicates thatthe crystals grew in open space, free fromimpingement except for the small area atthe wall of the barite hollow crystal.

Several possible explanations for theorigin of hollow barite crystals have beenproposed. The most obvious and initi-ally the most appealing hypothesis ispseudomorphism, which suggests that thebarite was precipitated over pre-existingcrystals which have since been removedby solution. This explanation accountsfor the external morphology of thehollow crystals, their hollow character,and thin wall, but does not explain thepresence of the well-formed calcite crys-tals within them or the acicular bariteextending across the central void.Another hypothesis considers the hollowcrystals as shell-like remnants of pre-viously existing barite crystals, where thecentral portions have been dissolved out.If so, why were only the central portionsof the original barite crystal dissolvedaway? It is possible that the hollowbarite crystal is the primary product ofa growth phenomena and that the hollow

crystals are essentially unchanged fromthe time they were formed.

Barite is a common encr j.sting materialon large calcite crystals; its encrustinglayers may be as thick as 5 mm (fig. 15).The thickness of the barite on a singlecalcite crystal face is generally uniform,but the encrustations appear to have anaffinity for the interfacial joins and theterminations of the calcite crystals.

Microscopic Features. In thin section,tabular and bladed barite crystals arecharacteristically arranged in radiatingclusters and randomly-oriented, mattedaggregates (fig. 16). Plumose structuresare common (fig. 17), with each made upof many curved, frond-like crystal units,all with nearly the same crystallographicorientation. The slight variations oforientation give the individual unitsoptical distinction, and the overall effectis that the plumose structure has ex-tremely undulatory extinctions. Thistype of extinction is prevalent in thinsections of all barite found at PughQuarry.

Zoning is apparent in thin sections ofbarite crystals and crystal aggregates andresembles chevron strips, particularly inthin-sections (fig. 18). In these sections,thickness variations result in vivid inter-ference color differences with zones thatcan be seen clearly in both plain andpolarized light. In addition to thecolor zones, white opaque zones were ob-served in many barite crystals (fig. 19).They appeared to be depositional and areprobably not the result of secondary alter-ation. Hydrochloric acid applied to theopaque zones of barite did not indicatethe presence of carbonate. Frondel (1935)described a similar type of zoning inwhite opaque barite at other localities.His chemical analyses showed that theywere essentially pure barium sulfate.X-ray diffraction analyses confirms Fron-del's findings. The unusual appearanceof the zones is probably related to poorcrystallinity or to large numbers of fluidinclusions contained therein.

CELESTITECelestite was found only in the eastern

portion of the quarry. Gray-blue andblue celestite crystals occurred predomi-

Ohio J. Sci. OHIO BARITE AND CELESTITE '27

FIGURE 16. Thin section, crossed nicols. Randomly oriented, matted aggregate of barite crys-tals. (X 25)FIGURE 17. Thin section, crossed nicols. Plumose structure of barite. Note the numerous, frond-like crystal units. (X 25)FIGURE 18. Thin section, crossed nicols. Barite. Note chevron-strip zoning. (X GO).FIGURE 19. Thin section, crossed nicols. White opaque zones of barite. Note parallelism ofopaque zones. (X 25)

nately in the mineral zone, whereascolorless and white celestite crystalsoccurred in the quarry wall below themineral zone.

Relation to Host Rock. Examinationof thin sections of celestite crystals andthe associated matrix rock showed noevidence of any replacement betweendolomite and celestite. Celestite com-monly occurs as euhedral crystals, and isnot generally found as interstitial pore-filling material in the dolostone. Theinterface between celestite crystals anddolostone is sharp and no dolomite

rhombs were included in the basalportions of the celestite crystals.

Habit and Form. The gray-blue andblue crystals are prismatic to blocky(fig. 20), occurring as well-formed sepa-rate individuals as much as 1 cm in maxi-mum dimension. These crystals aresimple morphologically. The {100} and{011} forms, with minor modification by{101}, dominate the morphology of nearlyall the gray-blue and blue crystals. Withgenerally minimal development, {001}and {210} are present on a few of thecrystals. The major pinacoid form,

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FIGURE 20. Blocky blue celestite on dolostone. Note the striations on the [1001 pinacoid the[101] prism, the [011], and the [001] pinacoid. (X 4.3)FIGURE 21. Celestite on dolostone, colorless to white bladed crystals arranged in a rosette manner.(X o.4)FIGURE 22. Thin section, crossed nicols. Celestite. Blocky, blue-gray crystal, Bxa orientationNote the distinct zoning parallel to the [011]. ( 60)FIGURE 23. Celestite, fluorite, and calcite on dolostone. Fluorite is paragenetically earlier thanceletite. (X 3.5){100}, is invariably striated and com-monly shows marginal development of{h0-£}. The numerical values of the{hO }̂ form are 0 = 90° and p = 84°.

The colorless and white crystals aretabular to bladed and occur as distinctindividuals and as compact clustersresembling rosettes (fig. 21). The indi-viduals are typically less than 5 mm inmaximum dimension, and the rosette-like

clusters are generally about 1 cm indiameter. The major form is the strong-ly striated {100} pinacoid, but {101} and{011} prism forms are invariably presentas well. Several {hk-̂ } forms of minimaldevelopment were observed on thesecrystals, but could not be preciselydenned.

Microscopic Features. Oriented thinsections perpendicular to each of the

Ohio J. Sci. OHIO BARITE AND CELESTITE 29

three principal axes were prepared fromthe blue celestite crystals. Narrow lightand dark zones were readily observableunder low magnification in Bxa sections.These zones were parallel to the {011}form, which is the most prominent formin these crystals (fig. 22). Additionalzones were parallel to {Oil}, the mostprominent cleavage direction of celestite.The zones were not readily visible whenb and c axes oriented parallel with theaxis of the microscope.

Under low magnification with crossnichols, the zones appeared to be 0.005to 0.01 mm in width. Under highmagnifications in plain light, the lightand dark zones were resolved into manyvery fine light and dark bands with aminimum width of 0.001 mm. These finebands were surprisingly uniform in widthand continuity, and are parallel to {011}.

The precise nature of the wide andnarrow zones is not known. The finebands may be similar to the bandsdescribed by Roedder (1969) occurringin celestite crystals from Clay CenterQuarry, located about 30 miles to thenortheast in Clay Center, Ohio. Elec-tron probe analysis for barium and stron-tium revealed that the light bands con-tain more Ba than the dark bands; andRoedder concluded that the light anddark bands result from small differencesin their indices of reflection caused bythe differences in their Ba content, sug-gesting that annual change in solution

chemistry was the most acceptable ex-planation for their origin.

Relationship of Celestite to Other Min-erals. Megascopic and thin section ex-amination of coexisting celestite and cal-cite crystals indicated that celestitecrystals were beginning to form prior tothe cessation of calcite crystal growth,and that the greatest amount of celestiteformed after cessation of calcite precipi-tation. No calcite crystals were foundperched on celestite. Intergrowths ofcelestite and calcite were observed onlyrarely. Fluorite was parageneticallyearlier then celestite (fig. 23), but nospecimens were obtained which dennedthe paragenetic relationship betweenbarite and celestite.

Acknowledgments. The authors are indebtedto Drs. James E. Bever and Charles Kahle fortheir assistance and advice. Special thanks goto the Pugh Quarry Company for its coopera-tion.

LITERATURE CITEDFrondel, C. 1935 Vectorial chemical altera-

tion of crystals. Amer. Mineral. 20: 852-862.Parr, D. F. and L. L. Y. Chang 1977 De-

scriptive mineralogy of Pugh Quarry, north-western Ohio: Marcasite and pyrite. OhioJ. Sci. 77: 213-222._

1978 Descriptive mineralogy of PughQuarrv, northwestern Ohio: Sphalerite.Ohio j . Sci. 78: 272-279.

1979 Descriptive mineralogy of PughQuarry, northwestern Ohio: Calcite, dolo-mite, and fluorite. Ohio J. Sci. 79: 24-31.

Roedder, E. 1969 Varve-like banding of pos-sible annual origin in celestite crystals fromClay Center, Ohio. Amer. Mineral. 54: 796-810.