Minerals of the Bluffton Stone Co. Quarry by Joseph W. Vasichko

Introduction        Several different dolostone quarries situated in the Findlay Arch mineral district of Northwestern Ohio have yielded superb quality specimens for private collectors and museums.   Although the mineralogy of these quarries is generally limited to a small suite of species, specimens from this district are often unique to their locality.   However, decreasing accessibility to collect in these quarries has limited the number and overall quality of Ohio specimens available.    In recent years, the Bluffton Stone Company quarry located on the South side of Bluffton in Allen County, Ohio has produced many outstanding and locality unique fluorite specimens as well as small to micro crystals of sphalerite, calcite, dolomite and pyrite.  Rarely, and usually in combination with the more sought after fluorite, miniatures of these lesser accessory minerals have been recovered.   Unfortunately, this prime locality has received little to no recognition from collectors outside the state.  In fact, to give Bluffton specimens greater appeal to world-wide collectors who are familiar with only a handful of Ohio localities, many of these pieces are misidentified or, even worse, re-identified from another locality by either inconsiderate or unknowledgeable dealers.    However, considering the rarity of quality pieces from Bluffton, many specimens from this little-known quarry are more valuable than similar pieces from more famed localities.

Fluorite with phantom purple faces (largest crystal is 1.4 cm)  Bluffton Stone Co. Quarry

Bluffton Stone Co. Quarry  Photo 2000

History   Dolomitic Limestones have been quarried in Allen County, Ohio since the mid Nineteenth Century.  Most of these early quarries were shallow and specialized in building stone and flagstone, which was needed for fast growing communities of the time such as Lima and Findlay.  Several small quarries along Riley creek near Bluffton were operated in the late 19th and early 20th Century for flagstone and lime burning.  Often, the lime burning furnaces were adjacent to these shallow pits.  Since the work was hazardous and the profit was slim, most of these small quarries and lime furnaces were owned and operated by one person.    In the short period between 1915-1930, three major quarries opened in Allen County, including quarries in Lima, Delphos, and the Bluffton Stone Co. quarry just South of Bluffton.   These larger quarrying companies, with the  ability to employ as many as fifty men and the advantage of pneumatic tools, put all other smaller operations out of business.   Since that time, the Bluffton Stone Co. has quarried material for flagstone, aggregate and agricultural lime.  Currently, the operation is a three level pit on the East side of I-75 just South of Bluffton.  A small tunnel underneath the freeway connects this newer pit with the original quarry.

Geology       The material quarried by the Bluffton Stone Company for aggregate and flagstone is the Tymochtee dolomite and perhaps other unidentified dolomitic limestones of the Salina Group.  These dolostones represent the youngest of the Silurian deposits in Ohio, regularly overlaying the older Greenfield and Lockport dolomitic limestones.  Except for the upper 6 feet of the strata which have weathered to tannish-brown, most of this Tymochtee dolostone is a uniformly grayish-blue, a much darker color than the lighter gray Lockport or Greenfield dolomite.  Unlike the more fossiliferous Greenfield and Lockport dolomitic limestones, these sediments, visible in several quarries in the area including the quarries at Findlay, Lima, Rimer, Huntsville and Delphos, host little evidence of Silurian life.   Occasionally, algal reef structure causes a ripple like appearance to the otherwise level bedding plane of the Tymochtee dolomite.  Fossilized mud cracks, raindrops and glacial pavement can be found in the talus piles on the upper level where the dolostone is typically shale-like and suitable for flagstone.  Stone quarried from the lower level of the pit for crushed aggregate is typically more compact with few vugs and little mineralization.

Front end loader moving flagstone on the upper level of the Bluffton Stone Co. Quarry              photo.....2001

Mineralogy      Mineralization of the Tymochtee dolomite in the Bluffton Stone Co. quarry generally occurs in one of two ways; as crevasse fillings perpendicular to the bedding plane, as crystals and fillings of vugs and small pockets.  While there is some debate about the origin of the metal rich solutions which formed these minerals, it is believed that mineralization occurred post sedimentation.  The best crystals usually occur in the upper twenty feet of the quarry in small pockets which rarely exceed five inches in diameter.   Commonly, these pockets or vugs range from one to three inches.  Few crystals of any quality have been observed in the lower level of the quarry due to a lack of measurable vugs.  This limits mineralization to fractures in the dolomite which give little opportunity to crystal growth.    Minerals which have been reported from the Bluffton quarry include asphalt, calcite, dolomite, fluorite, gypsum/anhydrite, melanterite, pyrite, sulfur and sphalerite.  Of these, the most desirable is a variety of clear fluorite with phantom purple crystal faces which vanish and reappear depending on the angle at which the specimen is viewed.

Fluorite in vug of dolostone (largest crystal is 1.4 cm) Bluffton Stone Co. Quarry

Fluorite with golden brown phantom center (crystal is .8 cm) Bluffton Stone Co. Quarry

Fluorite  CaF2           Most if not all of the dolostone quarries in the Findlay Arch mineral district produce specimen quality fluorite crystals.  However, very few of these quarries see the variety of fluorite habits which occur in the Bluffton Stone Co. quarry.  Fluorite from this locality typically forms cubic crystals, some with trisoctahedral modifications, in one of the following ways: single crystals, crystal clusters, or crystal linings of pockets.  Multiple growth cubic crystal clusters and plates are common in highly mineralized areas of the quarry.   Several different colors of cubic fluorite crystals have been reported including purple, pink, clear, white, yellow, gold and brown to brownish black.   Occasionally specimens show multiple generation growth either as phantom crystals or as contrasting crystals grown on previously existing fluorite.   Because there are so many different habits of fluorite in this quarry, it is conceivable that the metal rich solutions which form fluorite crystals may have been introduced to these dolostones on multiple occasions. The photograph to the left shows second generation clear fluorite which has grown on an existing honey-brown fluorite cube creating and unusual phantom for this locality.

Brown Fluorite    Recent quarrying on the upper level of the Bluffton Stone Co. quarry has produced some outstanding specimens of golden to dark brown fluorite crystals usually as pocket linings, but occasionally as single crystals.   Single brown fluorite crystals have been reported up to 5 centimeters from this locality.   Most brown fluorite specimens from this quarry show some degree of multiple growth crystal development.  Multiple growth in Fluorite crystals can occur in two ways.  Multiple cubic face growth is present when the crystal faces are cubic, but one or more of the faces do not form a perfect square or rectangle(B).  Multiple step growth is evident when individual crystals appear to be an assemblage of "building block" smaller crystals(C).  Although common in other quarries in the district, rarely will brown fluorite crystals form perfect cubes in the Bluffton quarry(A).   In addition, much of the fluorite is slightly to severely weathered or water etched.    This is an unfortunate result of crystal growth occurring too near the surface.  Pockets and fillings of brown and golden fluorite have been observed less than two feet below the top of the quarry.  Internal fractures, along with any degree of weathering, give many fluorite specimens a dull luster.  Well preserved vitreous brown fluorite crystals seem to develop slightly deeper in the quarry and often show brilliant iridescence. Fluorite with sharp iridescent faces (center crystal is 1.8 cm) Bluffton Stone Co. quarry

Multiple Growth Diagram: A) Perfect Cubic crystal   B) Multiple cubic face growth crystal      C) Multiple Step growth crystal Fluorite showing multiple step growth crystal development (largest crystal is 2.1 cm) Bluffton Stone Co. quarry

Purple Fluorite   As mentioned earlier, the Bluffton Stone Co. quarry is renowned for purple fluorite crystals, a color seen in very few localities around the state including the more famous Auglaize quarry in Paulding County.  While also noted for purple phantoms and iridescent brown fluorite, quality specimens from the Auglaize quarry have been widely available to collectors.   In general, outstanding purple phantomed fluorite specimens from the Bluffton quarry are significantly less common.  The highly localized occurrence of this habit in the quarry along with typically small pocket size and the brittle nature of these crystals attribute to the scarcity of outstanding examples of purple fluorite from this locality.  Outstanding purple phantoms came from the South end of the pit in a zone no longer being quarried.   Even at that the time, outstanding purple fluorite specimens were difficult to collect.   Recent quarrying has produced very few indications of purple phantom fluorite.  However, one small boulder pile still produces good specimens with considerable work.

Fluorite with sphalerite in vug of dolostone (largest crystal is .8 cm) Bluffton Stone Co. quarry

Fluorite with phantom purple faces (crystal is 1.1 cm)  Bluffton Stone Co. Quarry

Phantom Development      The classic fluorite crystal from the Bluffton quarry is a water clear cube with a thin purple phantom directly beneath the crystal faces.   These phantoms, completely unlike phantomed fluorite from the Auglaize quarry, are only visible from certain viewing angles.   However, this thin layer of purple color is enough to tint the entire crystal.   When viewed perpendicular to any crystal face, the phantom creates a deep purple outline of the crystal shape which disappears as the specimen is turned.   There has been much debate on the cause of this type of phantom and whether the purple phantom in these crystals formed towards the end or possibly after the completion of crystal development.   Purple phantomed fluorite crystals from the Bluffton Stone Co. quarry may develop as single crystals, clusters or as pocket linings similar to specimens of brown fluorite.  However, in contrast with the trends of brown fluorite from this quarry, these crystals rarely show evidence of multiple growth crystal development.   Occasionally, phantomed crystals from Bluffton are internally fractured or water etched, but in general remain translucent.    Although quite uncommon, crystals with this type of phantom have been reported up to 2 cm in size.   The photo to the left shows a classic example of phantom development from this locality.

Clear Fluorite      The Bluffton Stone Co. quarry is equally well noted for outstanding specimens of colorless to water clear fluorite as for phantomed crystals.   With few exceptions, Ohio fluorite crystals suffer from heavy internal fractures.   However, occasional crystals from Bluffton rival the clarity of crystals from Walworth, New York.  Colorless crystals have been reported, although rarely complete, up to 3 cm in size.    Many crystals from this locality are naturally colorless, however purple phantomed fluorite can fade to colorless after much exposure to sunlight.   Under prolonged exposure to sunlight, purple phantoms will fade to light lavender, pink and eventually clear.   Often, colorless crystals from Bluffton will form in the same pocket as purple phantomed Fluorite crystals.   Water clear, colorless fluorite crystals are quite uncommon.  Most naturally clear crystals from the Bluffton quarry have a hint of either purple or yellow.  The photo to the right shows a gem-like ruby-jack sphalerite crystal as seen through a 1.4 cm fluorite cube.   This crystal shows a slight amount of natural purple tint, but clarity is typically unaffected by color.

Clear fluorite with sphalerite  (crystal is 1.4 cm)  Bluffton Stone Co. Quarry

Fluorite Crystal Modifications       One of the most intriguing aspects of  fluorite crystal development in the Bluffton Stone Co. quarry is the appearance of several crystal modifications.   Ohio fluorite crystals typically form perfect cubic crystals.   Modified fluorite crystals have uncommonly been reported from other localities throughout the state.   However, no other known locality has produced the quantity of fluorite specimens with crystal modifications.   In general, these modifications are very slight and give many crystals an appearance of having a rounded or broken Fluorite with trapezohedral  modification (Modification is 1.3 mm on a 2.9 cm cube) Bluffton Stone Co. Quarry corner.   Only after careful  inspection with a hand lens or microscope can  these modifications be correctly identified.  Three distinct modifications have been recognized to exist in fluorite crystals from the Bluffton quarry; trapezohedral, trisoctahedral, and hexoctahedral.    The diagram below displays these three modifications to a greater degree than typically observed in fluorite from this locality.  The most common of these is the cube with trapezohedral modifications.  1) Cube with Trapezohedron  2) Cube with Hexoctahedron   3)Cube with Trisoctahedron (Crystal forms as described by Edward Salisbury Dana) Note: each of the drawings above represent a 70-30 ratio between crystal forms.   In general, fluorite crystals from the Bluffton Stone Co. quarry show less than five percent modification giving crystals a rounded appearance as illustrated in the cube to the left.   Occasional smaller crystals will show a greater degree of modification.

Fluorite with clear hexoctahedral modification of the   cube and also diploidal modification of the hexoctahedron (Modification is .6 mm on a 1.3 cm cube) Bluffton Stone Co. Quarry Most modified crystals typically show less than 5 percent modification of the cube. For example, a 1 cm cube would have a modification of .5 mm or less.  Rarely, and usually on smaller crystals, modifications will be greater.  Modifications have been observed on every color of fluorite from this quarry, but are most prevalent in golden yellow, brown and clear crystals.  Occasionally crystals will show more than one modification, either on alternating corners of the cube or as more complex modifications of each corner.  The photo above shows two modifications; a clear hexoctahedral modification of the cube in combination with a diploidal modification of the hexoctahedron.  Notice the difference in texture between the two crystal forms.

Fluorescence of Fluorite        Trace petroleum has been identified as the activator in fluorescent barite, calcite, celestite, fluorite, gypsum and strontianite from the Findlay arch mineral district.   These minerals, when fluorescent, are similar in fluorescent color; cream to greenish or bluish white.   As a rule, all golden to brown fluorite from the Bluffton Stone Co. quarry, and in general the state of Ohio, fluoresce various shades of cream-white under both long and short wave ultraviolet light.  Many brown fluorite specimens will show more than one shade of cream-white under short wave ultraviolet light.    Some clear to pale yellow fluorite is also fluorescent, but most, along with generally all purple varieties, are not.   Typically, masses or cleavages of dark brown fluorite are more responsive to UV exposure than complete crystal faces.  The photo to the right shows a plate of dark brown fluorite crystals from Bluffton.  Notice the broken crystals at the top Left of the specimen fluoresce brighter than the crystal faces.    Clear crystals from this locality occasionally have phantom fluorescence.  Clear flourite crystals under SW ultraviolet light (largest crystal is .8 cm) Bluffton Stone Co. Quarry The centers of these crystals fluoresce brilliantly while the edges, although translucent, are non-fluorescent.  The photo to the left shows an example of this type of fluorescence.  All fluorescent fluorite specimens from this locality also display some degree of phosphorescence.   Many pieces will continue to phosphoresce for nearly thirty seconds.

(above)Brown flourite crystals under SW ultraviolet light (largest crystal is 3.3 cm on edge) Bluffton Stone Co. quarry (left) Mass of cleaved golden brown fluorite under LW  ultraviolet light (Specimen is 14 cm x  11 cm) Bluffton Stone Co. Quarry

Sphalerite ZnS   The Bluffton Stone Co. quarry has also been noted for producing well-formed crystals of sphalerite up to 1 cm.   Good miniature specimens of sphalerite from Bluffton are somewhat uncommon.  Typically, sphalerite from this locality will form individual crystals and crusts of crystals lining smaller vugs often, but not always, in association with clear and purple phantomed fluorite.  For this reason, most sphalerite from this locality is only suitable for micromounting.   These crystals are generally sharp, Golden sphalerite  (largest crystal is .1 cm) Bluffton Stone Co. Quarry gem-like and show well-defined hextetrahedral form, although many are rounded, stretched and distorted.  Rarely, sphalerite from this locality will show other tetrahedral forms. Few, usually larger, crystals will show slight  multiple growth and twinning.   The classic Bluffton sphalerite crystal is a simple hextatrahedron, somewhat limpid and deep wine red in color commonly called "ruby-jack".  However, crystals vary in color from light yellowish orange to nearly black.

Sphalerite "ruby-jack" showing  hextetrahedral form and classic gem-like red color  (crystal is .4 cm) Bluffton Stone Co. Quarry

Pyrite  FeS2        Although in the same Tymochtee dolomite as the C.E. Duff and Sons Quarry, a locality known for outstanding pyrite specimens, the Bluffton Stone Co. quarry rarely produces quality specimens of this common sulfide.   Unfortunately, most of the pyrite from this quarry comes from the lower level where the pockets are fewer in number and smaller in size.   In this portion of the quarry, most minerals mainly exist as crystalline crusts and seam fillings.    However, several different crystal forms of pyrite have been reported in the Bluffton quarry including cube, octahedron, pyritohedron, and diploid.   Of these, the most common form observed from this locality is pyritohedron.  As is common in pyrite from the State, most crystals show modifications of other crystal forms.   Extremely rare pyrite crystals have been found in the upper level of the quarry, often in combination with fluorite, dolomite or calcite.   Many pyrite crystals from Bluffton are iridescent and exist as individual crystals or linings of pockets similar to sphalerite.   The photo to the right shows an example of pyrite crystals from the Bluffton quarry.  Notice the iridescent stain on the five sided face and the presence of a small fluorite cube.

Pyrite showing 5 sided pyritohedral form (crystal is .2 cm) Bluffton Stone Co. Quarry

Calcite on fluorite with sphalerite (center fluorite crystal is .7cm) Bluffton Stone Co. quarry

Calcite  CaCo3        Many of Ohio's quarries have been long recognized for yielding outstanding specimens of calcite in multiple habits.   However, the Bluffton Stone Co. quarry seldom produces large specimens of calcite.   Occasional crystals, usually in the upper level, grow to several centimeters but often mostly or completely fill small pockets.   Well-formed, but smaller rounded rhombohedral crystals occur with clear and purple phantomed fluorite.   Most calcite from this locality is rhombohedral but scalenohedral crystals have also been reported.   Tan, yellow, clear, cream and white crystals have been observed in this quarry, but even the best calcite specimens usually have crystals no larger than 1 cm.  The photo to the left gives an example of simple rounded rhombohedral crystals.   This piece is also an excellent example of mineral assemblage from the quarry.  Mineral rich solutions deposited the purple phantomed fluorite crystals first, followed by the "ruby-jack" sphalerite and finally the rhombohedral calcite, showing three stages of deposition.   Much of the calcite from this locality does not fluoresce, but these smaller white rhombohedrons fluoresce bright bluish-white similar to some fluorite from the quarry.

Dolomite  CaMg(Co3)2      Surprisingly, with the abundance of dolomitic limestones in the Western half of the state, good dolomite specimens are somewhat uncommon from most quarries in Ohio.   Many quarries in the Findlay arch mineral district produce only microscopic dolomite crystals.   Two localities which are known for producing quality specimens of this under-appreciated carbonate are the France Stone Co. Custar quarry in Wood County (formerly known as the Pugh quarry) and the C.E. Duff and Sons quarry in Logan County.     The Bluffton Stone Co. quarry occasionally yields pure white to cream dolomite crystals in two rhombohedral habits; simple or curved.  Most dolomite crystals from this locality are small simple rhombohedrons of less than 2 mm in size.   Occasionally, curved or saddle-shaped dolomite crystals similar to those from the Duff quarry have been observed up to 1 cm.  The photo to the right shows an example of curved rhombohedral dolomite crystals from Bluffton.  The presence of one small pyrite suggests that the piece originated from the classic Duff quarry.   However, upon closer inspection the pyrite is  pyritohedral, a crystal form only rarely seen at the Duff quarry, but common for pyrite from the Bluffton quarry.

Saddle shaped dolomite with pyrite (largest dolomite crystal is .9 cm) Bluffton Stone Co. Quarry

Collecting Tips    If lucky enough to be allowed a visit to the Bluffton Stone Co. quarry, consider a few of the following collecting tips.   In addition to hard hat, safety shoes and safety glasses, wear leather work gloves.   The rocks can be sharp and this will keep your hands from possible cuts.   The Tymochtee dolomite is very dense and extremely hard, although it will tend to split along the bedding plane.  A four pound crack hammer and chisel will break most smaller rocks.   Don't assume that the best specimen needs to be dug out of the wall.  Often the nicest specimens are found in the many boulder piles on the floor of the pit.   In fact, the best crystals are usually inside larger boulders.   A sledge and wedge are generally the best way to go after quality specimens in the boulders.   Look for mineralized boulders.    Typically, boulders with broken mineral pockets on the outside have a greater chance of still having good crystals on the inside.   Bring paper and buckets to carefully wrap specimens.  Remember, finding a nice crystal is only half the battle, getting it home in one piece is the real challenge.   Also, check over the freshly blasted talus piles, but be careful.   These piles are often unstable to walk on.  With much work, a typical day in the Bluffton Stone Co. quarry can yield several good specimens.  However, don't expect to walk around and stumble on a $100 dollar rock.  Collecting quality specimens is hard work.  Bring a collecting buddy and work together.  Two collectors can do 10 times the work of 1.   Always be mindful of where you are hammering.   If your chisel drives into a pocket it is likely to destroy any and every crystal inside.  Good luck.

Rockman Joe among the boulders Bluffton Stone Co. Quarry July, 20 2002

    This article in no way grants the reader permission to collect in the Bluffton Stone Co. quarry.  Permission must be obtained before entering any active mining area or collecting on any posted private property.
 

References Carlson E.H., 1991, Minerals of Ohio: Ohio Division of Geological Survey  Dana, E.S. and Ford, W.E., 1932, A textbook of Mineralogy( 4th ed.):New          York, John Wiley and Sons Janssens, Adriaan, 1977, Silurian rocks in the subsurface of northwestern           Ohio: Ohio Division of Geological Survey Report of Investigations 100 Korbel, P. and Novak, M., 1999, Minerals Encyclopedia, Rebo International Milner, Gloria L, 1989: History of Allen County, Davenport press Stith, David A. 1977, Limestone in the Tymochtee Dolomite: Ohio Division          of Geological Survey Stout, W.E. 1941, Dolomites and Limestones of western Ohio: Ohio Division           of Geological Survey Bulletin 42 Wolfe, M.E., 1997, Report on Ohio Mineral Industries, Ohio Division of           Geological Survey

Fluorite with Sphalerite in vug of dolostone (largest crystal is 1.0 cm) Bluffton Stone Co. quarry