Ohio Collector's Series       v.1   art.4
Mineralization 
of Geodized  Brachiopods

 Georgetown, Brown County, Ohio

by Joseph W. Vasichko
Introduction
    Most active Ohio fossil collectors are familiar with collecting at the shale-like limestone road cuts in the vicinity of Georgetown, Ohio, a proven bountiful resource for well preserved Ordovician age fossils.  This classic Ohio fossil locality has been a long-time favorite among Ohio fossil collectors for two simple reasons; ease of access and a readily available abundance of good specimens.  However, while fossil enthusiasts have been reaping the rewards of this old locality, mineral collectors have been missing out on a prime opportunity.  Although this locality is not generally linked to any distinct Ohio mineral district, it has been known to produce a surprising assemblage of mineral species.  It appears, mineral collectors have been trained into thinking that Ohio mineral collecting is limited to dolostone quarries in the Findlay Arch and Serpent Mound mineral districts.  This misconception has allowed many Ohio collections to become stagnant and unable to grow, as quarry collecting is no longer regularly available and quality old specimens from classic quarry localities are becoming more and more scarce.  Moreover, an Ohio collection replete with Findlay arch minerals alone is void of diversity and not truly representative of Ohio mineralogy.  To build a more complete Ohio collection, diligent Ohio mineral collectors should seek this type of collecting locality.  While the possibility of unearthing a museum size specimen from this locality is unlikely, the probability of recovering a quality locality example of several different mineral species remains quite high. 

Calcite and Dolomite in Geodized Platestrophia Brachiopod
(specimen Joseph W. Vasichko)
specimen measures 5.3 cm x 5.1 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 
History
    Situated in the heart of Brown County, Georgetown is best known as the boyhood home of Ulysses S. Grant, who once remarked on the abundance of fossils in the local streams.  These fossils are found predominately in a large strata of thinly bedded limestone.   In the 19th and early 20th centuries, Brown County farmers used this highly fossiliforous limestone to build uniquely stacked rock fences.  Some of these fences served to pen livestock, while others were used to preserve the sparse soil.  Many of these fences have withstood the test of time and can still  be seen throughout the surrounding area.  Due to the high relief of the area, most of the main roads to Georgetown began as toll roads.  With the invention of the automobile, many of these roads had to be rerouted to reduce the number of curves and steep hills.  The Hamersville-Georgetown road at Bald Point hill proved to be difficult to reroute.   Engineers decided it would be best to cut through the hill and reduce most of the curves.  In the 1920's, construction of Ohio Rt. 125 had begun, but it was not finished until 1934.   During the construction of the new road, many fossil specimens were collected and preserved in private collections and museums.  This sparked a flood of collectors to the area in the 1930's. However, the best collecting opportunity was yet to come.  With heavier 
Travelers on the Hamersville-Georgetown Road at Bald Point Hill near the
current collecting area on St. Rt. 125 west of White Oak Creek
(Photo c. 1925)
commercial truck traffic in the 1960's, a better road was needed.  It took approximately 4 years in the late 1960's to cut a straight 4 lane road through Bald Point Hill.   The removed material was leveled out and used to shore up the new bridge across White Oak Creek.  The resulting road cut provided collectors with plenty of fresh material to explore.  Currently, the best geodized brachiopod collecting area is a long high cut on the South side of Ohio route 125 West of White Oak Creek.

 


Road cut outcrop; layers of the Ordovician shale limestone
St. Rt. 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 Geology
    The Ordovician shales and limestones at Georgetown are generally accepted as one or more members of the Bull fork formation.   The Bull Fork formation encompasses the Waynesville, Arnheim, Whitewater and Liberty formations, however the rocks exposed at Georgetown are likely from the latter two.  These rocks lie just beneath the Drakes formation all of which are members of the Mohawkian-Cincinnatian series, approximately 450 million years old.  These rocks are exposed throughout much of Southwestern Ohio, South Eastern Indiana and North Central Kentucky, on the pinnacle of the Cincinnati Arch.   In general, the bluish gray limestones and shales of this group are very thinly bedded and highly fossiliforous. The most recognizable of these fossil species are Brachiopods, Trilobites, Cepholopods, Bryozoa, Crinoids, Eurypterids and Horn Corals.  Layers of this dense fossiliforous limestone up to 1 foot thick, but on average only 2 inches, are interrupted by a softer clay-shale.  Little exploration has been conducted on the practicality of mining the clay-shale.  A far superior clay-shale bed exists throughout much of Eastern Ohio.  The limestone of this group is generally unsuitable for any aggregate or lime need as better and purer dolostones lie in the nearby Silurian age rocks. 

 
Mineralogy
    Unlike, Ohio's Silurian dolostones, the dense limestones of the Bull Fork formation are virtually void of pockets.  Most of the mineralization, at this locality, occurs when the hollowed out centers of fossils, such as Brachiopods, Eurypterids, Cephelopods and Trilobites, are geodized or completely filled with Calcite.  These fossils vary in color from dark bluish gray to light tan.   In many ways, the mineralization of these hollow fossils resembles typical Midwestern geodes.  Typically, the best geodized centers are found in the larger Platestrophia Ponderosa, a brachiopod which occasionally grew to more than 3 inches.   The average size for brachiopods found at Georgetown is 1 inch.   The current theory is that after the animals decayed, those with complete and sealed skeletal shells allowed a hollow space to form in the rock.  This hollowed-out center allowed a space for mineralization to occur.  Those skeletal shells which were unsealed or incomplete were filled with sand and clay and became solid stone during the lithification process which formed this shale limestone.   For this reason, in the best zones approximately 90 percent of the complete brachiopods are mineralized.   Complete, larger and rounder Platestrophia Brachiopods have the greatest potential for geodized centers.  Complete, but flattened, Platestrophia Brachiopods do not usually have a large enough space for crystal growth and are usually filled with Calcite and other minerals. Geodized brachiopods have been observed in most layers of the shaley Limestone.   However, the best geodized fossils tend to form in the thinner soft shale layers and are often in clusters.   As opposed to most Midwestern geodes, which are typically lined with Quartz, the hollowed out centers of these fossils were first lined with small Calcite crystals.  These Calcite geodized fossils were again mineralized, sometime later, with a surprisingly large assemblage including; Barite, 2nd Generation Calcite, Celestine, Dolomite, Ferroan Dolomite, Goethite, Marcasite, Pyrite, Quartz, Sphalerite and Strontianite.   While geodized brachiopods are not nearly as common as quartz geodes found in many midwest localities, a larger percentage of the Calcite geodized brachiopods at this locality are hollow and have multiple minerals.
Cluster of Geodized Platestrophia Brachiopods trapped in shale
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio


Common Platestrophia Brachiopods
(Brachiopods vary in color in each layer of the strata.  Often the 
lighter colored fossils have a pearly sheen.)
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 
Calcite CaCO3
  Although a rather usual mineral throughout much of Western Ohio, Calcite geodes are a highly uncommon occurrence.  Unlike many midwestern states where Quartz geodes are widespread and abundant, geodes of any type are a rare find throughout the state.  The Calcite in these geodized brachiopods formed in two or more generations.  The first generation of Calcite forms a coating of drusy appearing crystals completely lining the hollow interior of the fossil.  While rare doubly terminated crystals are occasionally found, most first generation Calcite crystals are well formed clear white to grayish brown, singly terminated scalenohedrons or scalenohedrons with rhombohedral modifications.  Typically, first generation crystals are no larger than 1/4 inch.   These crystals are generally nondescript and relatively uninteresting  in comparison to Calcite specimens from other more famed localities 

Doubly Terminated Scalenohedral Calcite
(specimen Joseph W. Vasichko)
crystal measures .3 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 throughout the state.   The photo to the left shows a rare first generation doubly terminated scalenohedral Calcite crystal.  Although the crystal faces are slightly imperfect the form is still easily recognizable.  To the right, a fine example of the sequence of mineralization in these geodized brachiopods.  This brachiopod was first mineralized with scalenohedral, clear, Calcite.  Second, a blade of Celestine grew on the first generation Calcite.  Sometime later, a larger second generation pink scalenohedral Calcite grew through the pocket and encompassed the Celestine.

2nd Generation Calcite with Celestine in Geodized Platestrophia Brachiopod
(specimen John D. Vasichko)
Calcite crystal measures 2.1 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 

1st and 2nd generation Calcite in Geodized Platestrophia Brachiopod
(specimen Joseph W. Vasichko)
specimen measures 3.9 cm x 3.0 cm
Highway 125 Road cut North of Straight Creek
Georgetown, Brown County, Ohio		 2nd Generation Calcite
  In general, most second generation Calcite crystals, at this locality, are larger and far more aesthetic and diverse in form.   Brachiopods with larger complete and undamaged second generation crystals make very attractive specimens.  Usually forming more colorful crystals, both scalenohedral and Scalenohedral with rhombic modification 2nd generation Calcite crystals have been observed in the Georgetown road cuts.   Several distinct second generation Calcite habits have been identified in the geodized fossils at Georgetown.  However, the more striking second generation Calcite specimens are those with multiple growth, twinned or phantomed crystals.  Quite commonly, the second generation Calcite crystal will grow across the cavity and is difficult to save as a presentable specimen.  Brachiopods from separate strata tend to form different habits of second generation Calcite.  Geodized brachiopods in the same strata typically have similar second generation Calcite growth. Although typically not in specimen quality, brachiopods with more than one habit of second generation Calcite have been recovered at this locality.   Unfortunately, about 1/3 of all mineralized brachiopods have been mostly to completely filled with second generation Calcite.   On average, complete brachiopods with lighter tan colored shells are most likely to have been mineralized with second generation Calcite.

 

Multiple Growth 2nd Generation Calcite
(specimen Joseph W. Vasichko)
crystal measures 1.3 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 Multiple Growth Calcite
     Perhaps the most interesting Calcite specimens are the multiple growth second generation crystals.  This habit of Calcite is most easily recognized by the abundance of terminations on one or both ends of the crystal.  However, the majority of Calcite crystals in this habit are only singly terminated.  These crystals also have the distinction of being a deeper yellow brown color than the contrasting pale, clear first generation crystals.   Regrettably, it is extremely difficult to collect a decent specimen of this particular habit of Calcite due to the size of the crystal in comparison to the size of the cavity.  Often, this habit of Calcite fills more than 3/4 of the fossil cavity.    In addition, while this is a common growth form at many statewide localities, it is a highly uncommon habit at Georgetown.   Add these conditions to the likelihood of breaking open the fossil cavity in the right direction so as to avoid breaking through the crystal and it becomes fairly evident why few of these specimens are preserved.  The photo to the Left displays a typical multiple growth crystal from Georgetown.  Notice the size of the crystal in comparison to the overall size of the cavity.  Calcite crystals of this habit, which have been saved, are generally similar in size to this one in comparison to the overall size of the fossil cavity.

 
Twinned Calcite
   Although Calcite is known to form crystals in many habits throughout the state, twinned Calcite crystals are very rarely encountered at any Ohio locality.    Surprisingly, small stretched out twinned scalenohedral Calcite crystals are occasionally observed in geodized brachiopods from Georgetown.  These twinned crystals bare some similarity to 1st generation Calcite crystals from this same locality.  These twinned crystals are typically the same color and clarity of the average 1st generation Calcite.  Also, although twinned crystals have been observed up to 1 centimeter in size, the average twin is approximately a quarter of a centimeter, similar to most 1st generation crystals.  Because of these similarities, it is often difficult to tell 1st generation Calcite and 2nd generation apart at first glance.  However, the two are easily separable with the aid of a hand lens.  First, twinned crystals have a clearly visible twinning plane.  Twinned Calcite crystals, from Georgetown, are clearly scalenohedral in form, but are stretched out along the twinning plane creating a heart-like shape.  This shape bares absolutely no resemblance to 1st Generation Calcite.   The photo to the left displays one of these twinned Calcite crystals.  Notice the clear twinning plane and the overall shape created by the stretched scalenohedron.   The crystal above and slightly hidden behind the main crystal in the photo along with many other 2nd generation crystals in this pocket are also twinned in this same manner. 
Twinned 2nd Generation Calcite
(specimen Joseph W. Vasichko)
crystal measures .6 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 
Additional 2nd Generation Calcite Forms
  Other 2nd generation Calcite forms have been observed and more are possibly waiting to be discovered in geodized brachiopods of the Georgetown area.  Additional forms which have been identified at this locality include Scalenohedral crystals with rhombic modifications and phantomed crystals.  The first, modified Scalenohedral crystals, are easily identified by a "flattened" rhombohedral termination.  Even a slight rhombohedral termination disguises the dominant Scalenohedral form can easily 

Modified 2nd Generation Calcite, 
(specimen Joseph W. Vasichko)
crystal measures .9 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 cause the collector to misidentify the crystal as a Sulfate.  The crystal to the lower left exhibits this characteristic.   When viewed from an angle parallel to the the rhombohedral modification, this crystal greatly resembles Celestine.  The color and clarity of this crystal contribute to this similarity.  Rarely, brown phantoms have been observed in second generation Calcite crystals.  Typically, these phantoms are found in scalenohedral crystals with slight rhombic modifications that are less than one centimeter in size.  Although the phantoms in these crystals are often clouded and indiscernible, phantoms contribute to the color and aesthetics of small, lusterless and somewhat unappealing crystals. The photo to the right is a classic example of a phantom Calcite crystal from this locality.

 


Phantom 2nd Generation Calcite
(specimen Joseph W. Vasichko)
crystal measures .8 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 

Complete unterminated Celestine blade on Calcite
(specimen Joseph W. Vasichko)
crystal measures 1.9 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio


unterminated Celestine blades on Calcite
(specimen Joseph W. Vasichko)
field of view is 2.8 cm across
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 Celestine SrSO4
       One of the minerals most commonly associated with the State of Ohio is Celestine.   Many of the quarries located in the Findlay Arch district of Northwestern Ohio, including the quarries at Clay Center, Portage and Lime City, are famous for producing world class specimens of the species.  However, outside of the Findlay Arch Mineral District, Celestine is a relatively uncommon mineral around the state.  In that respect, the appearance of Celestine at this Southern Ohio locality is rather surprising.   In general, Celestine, at this locality, forms vitreous, slender, gray to bluish white unterminated blades.  Although the Celestine is intergrown with some, but not all, of the secondary Calcite, it is clear that the Celestine developed in these Geodized brachiopods after the 1st generation Calcite.   Approximately one in every 15 geodized brachiopods will have Celestine.   However, because of the inherent brittle nature of Celestine, the typically small geodized cavity size and the tendency of these crystals to grow across the cavity, preserving complete undamaged crystals is extremely difficult.   In addition, many of these bladed crystals show weathering cracks and etch marks contributing to the challenge of collecting undamaged specimens.  Much of the Celestine, found in the Georgetown road cuts, is severely weathered.  The weathering process transforms vitreous grayish blue Celestine blades to a soft white powder, perhaps Strontianite.  Any specimen with a fresh, large, complete and undamaged Celestine blade, from this locality, should be regarded as a choice piece.  The photo to the upper left displays an undamaged complete Celestine on Calcite from Georgetown.  Notice that the crystal is attached on both sides of the cavity.  Also, as is typical with most of these crystals, this specimen displays natural weathering cracks and etch marks.   This crystal is somewhat 
unique as it exhibits the beginnings of a termination visible in the lower left side of the crystal.  Very few bladed Celestine crystals, from this locality, show any termination.   The photo to the lower left displays more typical completely unterminated Celestine crystals.  Rarely, Celestine is seen as bursts of stacked intergrown bladed crystal clusters.  In general, these clusters are smaller and are occasionally terminated on one end.  An example of this habit is displayed in the photo to the right.   One other occurrence of Celestine has also been observed with Strontianite at the locality.
Celestine blades on Calcite
(specimen Joseph W. Vasichko)
crystal measures 1.9 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 
Strontianite SrCO3
     Strontianite, a carbonate closely related to Celestine, is one of the more intriguing micro minerals found at Georgetown.  The presence of Strontianite at this locality is most certainly related to the on going weathering process of Celestine.  As the Celestine is broken down, the Strontium forms small snow white radiating sprays of the carbonate.   As a rule, Ohio Strontianite forms tiny, orthorhombic, needle-like spires with curved tips, typically in bundles, sheaves, or ball-like sprays.   These curved tips are typically only noticeable under 15x magnification or greater.  At first glance, these sprays appear to be quite typical of Ohio Strontianite.  However, a quite unusual occurrence for Ohio Strontianite has been recognized in geodized brachiopods from Georgetown.  Upon close inspection of Strontianite clusters from this locality, one can easily observe that many of these radiating sprays are comprised of both Strontianite and Celestine crystals.   The Celestine is identified by bladed crystals with flattened or truncated terminations.  This crystal form is generally never employed by Strontianite.  Approximately fifty percent of the Strontianite sprays found in geodized brachiopods from the Georgetown area are intergrown with Celestine in this manner.  The photo to the upper right exhibits one of these larger sprays intergrown with Celestine.  A careful eye can discern both minerals in the photo.  The dark mass embedded in this Strontianite cluster is a sulfide, likely either Pyrite or Marcasite.  Although the typical Strontianite cluster measures no more than 1/16 inch, single Strontianite sprays have been recovered up to 1/4 inch.  Strontianite 

Strontianite "double ball" cluster
(specimen Joseph W. Vasichko)
crystal cluster measures .16 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 clusters, at this locality, tend to form in one of three identifiable habits.  The first and most common habit is a single radiating spray or "ball" cluster.   The specimen pictured in the upper right photo, although intergrown with Celestine, is an example of this habit.  The second two habits are more closely related.  Often, smaller and less developed sprays will resemble a bow tie.  These "bow tie" clusters appear to develop two sprays in opposite directions.  The photo to the lower right is a classic example of this development.  As this type of cluster matures, it often forms two connected ball-like clusters of equal size.  This "double ball" habit is displayed in the photo to the left. 

Strontianite and Celestine "ball" cluster on Calcite
(specimen Joseph W. Vasichko)
crystal cluster measures .3 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio


Strontianite "bow tie" cluster
(specimen Joseph W. Vasichko)
crystal cluster measures .06 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 
Dolomite CaMg(CO3)2 and Ferroan Dolomite Ca(Fe2+,Mg)(CO3)2
     The main constituent of Western Ohio sediments, Dolomite is one of the most common minerals found in the State.   The dolomitic limestones, in Ohio, which are actively quarried for aggregate and lime needs are comprised of microscopic Dolomite crystals.  Surprisingly, apart from the Duff and sons quarry in Huntsville and the Custar Stone Quarry near Weston, which produced decent white curved rhombohedral crystals, and large limestone septaria at various localities in the Ohio Shale, which produce a variety of Dolomite crystal habits, very few localities across Ohio are known for producing good crystal specimens of the species.   Geodized Brachiopods, from the shale-like limestone road cuts in the vicinity Georgetown, also produce fine curved rhombohedral crystals of Dolomite.  Unlike the smooth curved rhombohedral crystals which are occasionally encountered in the above mentioned dolomitic limestone quarries, most Dolomite crystals, from Georgetown, have clearly visible step growth and resemble curved stacked building blocks.  Rarely, smooth curved Dolomite crystals have been observed in these road cuts as well.  Although the typical crystal is approximately one centimeter in size, these curved rhombohedral crystals often will completely fill the geodized center of a brachiopod.   Dolomite crystals, at this locality, vary in color from cream-white to dark brown depending on the level of weathering which has taken place inside the brachiopod.  Fresh and unweathered specimens of Dolomite are generally 
somewhat translucent, cream colored and vitreous.   An example of this is pictured to

Iridescent Dolomite on Calcite
(specimen Joseph W. Vasichko)
crystal measures 1.1 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 the upper right.   Notice the clear step like growth habit of the curved rhombohedral crystal.  Typically, crystals which have undergone slight weathering are more flesh colored and have orange to brown terminations.  These crystals may also have a slight iridescent coating on the crystal faces.   The photo to the left displays a crystal with this iridescent coating.   Heavily weathered crystals turn dark brown to black showing that these are most likely Ferroan Dolomite.   The crystal displayed in the photo to the lower right has undergone an extreme amount of weathering.  Notice, the Celestine in the photo is equally weathered and has turned white.

Dolomite on Calcite
(specimen Joseph W. Vasichko)
crystal  measures .8 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio


Ferroan Dolomite  with Celestine 
(specimen Joseph W. Vasichko)
crystal  measures .5 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 

Barite with Dolomite and Celestine on Calcite 
(specimen Joseph W. Vasichko)
field of view is 1.6 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 Barite BaSO4
    The most uncommon mineral known to exist in geodized brachiopods, from the Georgetown area, is Barite.   In fact, good Barite crystals from the State of Ohio, are extremely difficult to find.   Barite, a sulfate similar to Celestine, has been observed as coarsely crystalline masses in limestone and ironstone septaria throughout the state, however only a few Ohio localities have produced any crystal specimens of the mineral.   Although Barite shares many physical characteristics with Celestine including weight, luster, crystal system and hardness, the two are easily distinguishable at this locality.  Celestine tends to form bluish gray to white bladed crystals.   Barite, at this locality, forms cream yellow to white rosette shaped crystal clusters.  Upon careful inspection, the crystals comprising these rosettes are somewhat translucent to water clear, however the overall appearance of the rosette is generally cream to white.   However, the vitreous nature of the small crystal faces causes the rosette to glisten.   The photo to the left displays one of these Barite rosettes.  Notice the association with Dolomite and Celestine.  This photo relays the ease of differentiating the two sulfates; Barite in the foreground under and in front of unterminated Celestine crystals.   This particular piece is a four mineral specimen, also a rare find for the locality and Ohio in general.

 
Pyrite FeS, Marcasite FeS and Goethite Fe3+O(OH) 
  Good crystal specimens of Iron Sulfide minerals are becoming increasingly difficult to find at this locality.  This, in part, is due to the fact that many of the exposed geodized brachiopods have undergone some amount of weathering.  The result is that most of the Iron Sulfides, Pyrite and Marcasite, have deteriorated into rusty masses of Goethite.  Both cubic and octahedral Pyrite are common in these brachiopods.  Although rarely seen, Marcasite blades also occur in  Calcite geodized brachiopods.   In most cases, the iron sulfide's crystal form has been blanketed by a coating of botryoidal Goethite, although occasionally the crystal is completely replaced by the Oxide.  The photo to the lower right exhibits a common example of this replacement.  It is likely that this Goethite needle was at one time a Marcasite blade.  The more common corrosion of Iron Sulfide is displayed in the photo to the upper right.  A Pyrite cube has been partially altered to Goethite and was, at one time, completely coated with the Oxide.  Part of the Goethite coating has crumbled away revealing the cube.  In the photo, one can clearly see both the cube, and the rind of corroded Goethite.  Also of interest in this photo, a small clear Dolomite crystal has begun to develop on the Pyrite cube, indicating that at least one generation of Dolomite was introduced after the Pyrite.  Marcasite blades and 

Goethite needle on Calcite
(specimen Joseph W. Vasichko)
crystal is .2 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 fans are less frequently observed than either Pyrite or Goethite.  This is perhaps due to the delicate nature of Marcasite blades.  Blades of Marcasite have been observed up to 4 millimeters tall and 1 millimeters wide, although the thickness of these crystals is nearly unmeasurable.  When viewed from the side, Marcasite blades, like these, are virtually undetectable.   A slight breath of air can easily damage a Marcasite blade.  Unfortunately, this thin fragile crystal shape rarely survives trimming.  Marcasite blades, from this locality can be reddish brown to black in color and often have a colorful mirror-like iridescent coating.  To the lower right is an example of a Marcasite blade.  This crystal is approximately .6 millimeters wide but less than .05 millimeters thick.

Goethite needle on Calcite
(specimen Joseph W. Vasichko)
crystal is .2 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio


Marcasite blade
(specimen Joseph W. Vasichko)
crystal is .25 cm tall
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 

Sphalerite on Calcite
(specimen Joseph W. Vasichko)
crystal is .7 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio		 Sphalerite ZnS
   Perhaps the most rarely seen sulfide, in geodized brachiopods from Georgetown, is Sphalerite.  Although approximately one third of geodized brachiopods will have Pyrite, Marcasite or Goethite, less than 1 in 100 will house Sphalerite.  Sphalerite, at this locality, tends to form small dark reddish brown to black crystal groups and masses.  This mineral will form smaller individual crystals, although this is not the norm for the species, at this locality.   Although some crystals may have a slight iridescent coating, most of the Sphalerite at this locality shows little or no corrosion or alteration.  Due to the typically small cavity size of geodized brachiopods and the low percentage of Brachiopods with this mineral, preserving an undamaged Sphalerite crystal can be difficult.   Sphalerite, when present, will generally more than half fill the cavity.    The photo to the left is an unusually fine example of Sphalerite from this locality.   This crystal is far smaller than the average Sphalerite crystal group from Georgetown.   Smaller crystal groups, like this one, typically have better color and make better specimens than large groups which generally can not be trimmed.   Also, while this crystal appears to have sharp crystal faces, most of the larger Sphalerite crystals encountered at the Georgetown road cuts are more crude and generally darker in color.   Although Georgetown, Ohio is relatively near the Serpent Mound Zinc Disturbance, the Sphalerite at this locality is most likely unrelated.

 
Georgetown Collecting Sites
    Although outcrops and stream beds in the vicinity of Georgetown are littered with the highly fossilliforous Ordovician age shale-like limestone, road cuts will have the highest potential for unweathered geodized brachiopods.   Stream beds and outcrops, in this area, may have geodized brachiopods, but many of the accessory minerals will have deteriorated.   On the map to the right, 4 road cut localities are pinpointed which have produced geodized brachiopods.  Site number one is a long high road cut on both sides State Route 125 West of White Oak Creek.  Most of the specimens used in this article came from site number 1.  Site number 2 is a long high road cut on the North side of State Route 125 East of White Oak Creek.  Since these two road cuts were excavated in the same year, specimens found at 

Site Number 1(West)
St. Rt. 125 West of White Oak Creek


Site Number 2(West)
St. Rt. 125 East of White Oak Creek

 this locality will be of equal quality.    Site number 3 is a short sloped road cut on both sides of State Route 125, a few hundred yards North of Straight Creek.  Geodized brachiopods are found near the top of this cut.   Site number 4 is a short shallow road cut on U.S. Highway 68 South of the intersection with State Route 125.   Geodized brachiopods are more infrequent at this locality, but, in general, the average cavity size is larger.  Although sites number 1 and number 2 have produced all of the mineral species listed above, sites number 3 and 4 have not been as well researched and may or may not produce all of the above mineral species.  Other road cuts around Georgetown and throughout Brown County may also produce similar mineral specimens.

(Above) 
        A topographic map of Georgetown, Brown Co. Ohio indicating the locations of 
4 road cut localities where Geodized Brachiopods occur.   The scale of this map is 
approximately 3/4" to the mile. 

(Below and to the Left)
        The locality photos of each of the four sites were taken in the fall of 2003.  Many of 
the specimens which were photographed for this article were collected during this same
year.   The direction attributed to each site number indicates the viewpoint of the
Camera.

Site Number 3(North)
St. Rt. 125 North of Straight Creek
Site Number 4(East)
US Hwy 68 East of  Georgetown 


 
Collecting Suggestions and Specimen Preparation
  One of the more difficult tasks in mineral collecting is properly preparing and trimming good specimens.  Although many of the complete Brachiopods, from this locality, will have partially to completely geodized cavities, not every specimen can be saved.  However, there are a few ways the collector can improve the percentage of specimens preserved.  First, examine the Brachiopod for any holes.  If there is a visible hole, one should examine the interior of the geodized brachiopod to see if there are any crystallized areas to avoid trimming.  Second, carefully inspect the fossil for any cracks.  If the specimen is cracked in any way, it is likely that this will be the first place the brachiopod will break open.  If the brachiopod is hollow, attempting to break it a different direction will likely cause additional cracks and holes to develop.  Third, if there are no cracks and no holes, try to imagine which way the specimen would look best if it were opened.  The careful collector will try to preserve the largest opening with the most complete crystals.  Remember to tap very lightly when trimming or opening.  Thin shelled Calcite Geodized Brachiopods break extremely easy.  By tapping lightly, the collector can notice the instance a crack begins to develop.  Once a crack develops, the collector should try to pry open the geodized fossil instead of continuing to hit.  This will help to preserve the crystals on the inside, while continuing to hit may crush the entire cavity.   Finally, when collecting keep an eye out for previously broken geodized brachiopods.  Occasionally, these can be cleaned to be nice specimens.  Also, previously broken specimens may indicate where a zone of geodized brachiopods may occur.  The most sure way to obtain good specimens is to collect numerous complete brachiopods.
1st and 2nd generation Calcite in Geodized Platestrophia Brachiopod
(specimen Joseph W. Vasichko)
specimen measures 5.3 cm x 3.8 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

 
Collecting Status, Tips and Collector Responsibility
     Current Ohio law permits roadside collecting on any rural, unposted State Route or US Highway, provided that collecting activities do not, in any way, interfere with normal and safe travel.   All of the localities listed in this article are currently open to fossil and mineral collectors.   Collecting is absolutely prohibited, at any time, along any Interstate or limited access highway.   Collecting is also not permitted in any area marked no standing, no parking or no stopping.  Collectors in any of these areas may be arrested and charged with trespassing.   Collectors should keep a few things in mind before visiting any roadside locality.  First, always wear gloves and sturdy shoes.  Snakes, including the timber rattler and copperhead, are frequently seen at road cut localities throughout the state.  Second, keep an eye on all moving vehicles.   Park your vehicle as far away from the edge of the road as safely possible and in sight of the collecting area.   The rule of thumb is 5 feet or more away from the edge of the road.   This is possible at all of the localities listed in this article.  Road cuts may be extremely slippery and unsafe when wet.   The most important thing one must remember is to use common sense at all times, when collecting.   Unsafe and inappropriate collecting habits can be cause for arrest at any location.  Finally, make sure you take all equipment and refuse, leaving only your tracks.   In the past, collecting areas have been closed due to inconsiderate and disrespectful visitors.  Collectors should consider themselves personally responsible for maintaining the access and availability of collecting localities.
St. Rt. 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio

     This article in no way grants the reader permission to collect at this or any other roadside locality.   It is the sole responsibility of the collector to know the current Ohio law regarding roadside collecting before planning a field trip to this locality.
 
References
Carlson E.H., 1991, Minerals of Ohio: Ohio Division of Geological Survey 
Brown County Historical Society, 1993, History and Families 1818-1993, 
          Brown County, Ohio
Dana, E.S. and Ford, W.E., 1932, A textbook of Mineralogy( 4th ed.):New 
         York, John Wiley and Sons 
Hansen, Michael C.,1996, Fossils of Ohio: Ohio Division of Geological Survey
La Rocque, Aurèle and Marple, Mildred F., 1955, Ohio Fossils: Ohio Division
         of Geological Survey
Morrow, Josiah and Beers W.H.,1883, History of Brown County, Ohio, 
        W.H. Beers and Co. Chicago
Newberry, J. S., 1873, Palaeontology: Ohio Division of Geological Survey, 
         Volume 1, Part 2
Orton, Edward, 1893, Economic geology, archaeology, botany, paleontology: 
         Ohio Division of Geological Survey Volume 7, 700 p
3 Geodized Platestrophia Brachiopods in Limestone
specimen measures 6.6 cm x 4.7 cm
Highway 125 Road cut West of White Oak Creek
Georgetown, Brown County, Ohio