Collecting Wurtzite Crystals  Negley, Ohio by Joseph W. Vasichko

Introduction         Concretion minerals, especially those from ironstone, are without doubt the most under appreciated of minerals species in Ohio.   Perhaps this can be attributed to the fact that most specimens generally only lend themselves useful to micro mounting.   The best specimens typically only display crystals measuring slightly over 1 millimeter and clusters to nearly 2 millimeters.   Wurtzite and Chalcopyrite, the most notable of these ironstone concretion minerals, have received little attention for this reason.    Coal strip mines in the vicinity of Negley in Columbiana County, Ohio have produced some of the finest Wurtzite specimens ever collected in the state.   Recently, Ohio collectors are beginning to take a greater interest in such minerals despite their magnitude.   Either the inaccessibility of many classic localities in the state is forcing their attention elsewhere or collectors are realizing the importance of these species to an Ohio collection.

Wurtzite....Negley, Ohio

History        Coal Mining in and around Negley Ohio began around 1910 with the founding of the Negley Coal Company.  The first operation was an underground tunnel and room excavation mine approximately 1 mile North of the village of Negley.  The mine produced approximately 15 tons of coal per day in it's first year of operation.  However, open pit coal mining did not begin in Negley until a greater demand for fuel coal forced existing mining companies to increase their production in 1929.  Since that time, coal and clay/shale have been mined intermittently South and East of Negley.  At one time, mines in the Negley area produced nearly 75,000 tons of coal and over 100,000 tons of clay/shale per year.  Currently, State Line Resources Inc. mines a clay/shale from several open pits approximately 2 miles Southeast of Negley on Co. Road 1026 off of St. Rt. 154.

2 Coal miners loading ore          Negley, Ohio(1948)

View of spoil piles at Negley operation . . . . . . . Photo 2002

Geology        The Pennsylvanian age sedimentary beds overlying the Lower Kittanning #5 coal around Negley consist mainly of course sandstones and gray to dark gray shales of the Allegheny group.  A short Vanport Limestone is also noticeable in the strata.  Ironstone/Siderite septaria and similar Iron rich limestone concretions, typically measuring up to 40 centemeters(16 inches), are prevalent in the Allegheny Shales directly overlying the coal beds.   Crystals and masses of Barite, Calcite, Chalcopyrite, Gypsum, Pyrite, Siderite, Sphalerite and Wurtzite occur in both septaria and concretions, but more thorough mineralization and better crystals occur in the wider seams of the smaller Ironstone septaria.    Approximately, 1 in 4 septaria has mineralization, but only 1 in 12 has shrinkage cracks large enough to support crystal growth.  Percentages are much lower in the flattened concretions.  Little mineralization is associated with the Sandstone or the Limestone.  However, single blades and rosettes of Gypsum and various efflorescences have also been noted on shales.

Mineralogy        Although the exterior of the concretions and the septaria differ slightly, similar minerals form in both under the same circumstances, only more predominately in the septaria.  Of the minerals occurring in the Negley septaria and concretions, the most sought after by Ohio collectors are Wurtzite and Chalcopyrite.   Although well formed crystals of Barite, Calcite, Pyrite and Sphalerite are available from this locality, crystals rarely exceed 3 millimeters.  Larger specimens of these species are readily available from other localities around the state.  In Ohio, Wurtzite and Chalcopyrite only form in these septaria and concretions and then only as micro crystals.     Many clay  minerals and various efflorescences have been observed in and around these septaria, but specimen grade pieces have not been recovered.    As a rule, internal crevasses in septaria will fill with multiple minerals.  Rarely a concretion will have crevasses with no mineralization.   Most septaria have pods and fillings of translucent to milky gray Barite often encasing various other minerals including Wurtzite.  Only a small percentage of septaria will have exposed crystals. Wurtzite in Barite .... Negley, Ohio

Top Photo: Broken septaria nodule -- (note:  internal crevasse creates a seam on the top exterior of the  nodule) Left Photo:  A Negley septaria  showing wide shringage  cracks Wurtzite bearing septaria.... Negley, Ohio

Wurtzite....Negley, Ohio

Wurtzite (ZnS)         The first reported occurrences of Wurtzite in Ohio were various different Clay pits and Strip mines in the Eastern part of the state.   Since that time, many localities have known to produce Wurtzite in varying degrees of quality and abundance.   Two famous  localities for Wurtzite crystals in Ohio are the Rt. 7 road cut near Alikanna in Jefferson County(no longer collectable due to recent road redesign) and the Old Gloucester clay pit near Jacksonville in Athens County(Flooded).  Unfortunately both of these localities are no longer in existence.   While there have only been a handful of localities known to produce specimens of Wurtzite it is possible and likely that others exist.   Any ironstone/siderite septaria or concretion in Eastern Ohio has the potential for producing Wurtzite crystals.

Occurrence       In the septaria at Negley Wurtzite typically occurs in Barite or Calcite and is usually associated with it's more common polymorph- black to deep, wine red Sphalerite.  Occasionally Wurtzite and Sphalerite will be inter grown, but this is not the norm.   Crystals are often sporadic throughout the crevasses in septaria and concretions and are attached lossely to the ironstone matrix or other minerals.  Even the most mineralized septaria will generally house no more than 100 crystals with less than 10 percent of those being complete.  Thin layers of clay minerals, likely kaolinite, often coat the fresh crystals and can often hide their existence.   Only upon careful inspection with a hand lens can most crystals be discovered.   A typical collecting day can yield several micro-crystals, however the percentage of Wurtzite which are complete and can be trimmed into an acceptable micro specimen is quite low.  Cleaning and preparation of these crystals for micro mounting takes a heavy toll on the crystals.  Often a quick rinse in water is enough to dislodge crystals from their matrix.

Wurtzite....Negley, Ohio (dihexagonal pyramidal crystal)

Wurtzite....Negley, Ohio

Formation        Wurtzite will form slightly translucent, burnt brownish red crystals in two different crystal systems in these septaria.  The most common form of Wurtzite is dihexagonal pyramidal(A).  Rarely a crystal will form a true ditrigonal pyramid(B).   Dihexagonal pyramidal crystals can occasionally be misidentified as ditrigonal pyramidal crystals  without careful examination.   It is not uncommon for the crystal faces to be unequal or distorted creating an illusion of a ditrigonal pyramidal crystal(C).   In either case one of pyrimids is truncated or shortened causing an uneven ratio between the two pyramids.  The truncated pyrimid can develop a termination or can remain incomplete.  The photo to the left displays two crystals, one with a  truncated pyrimid showing termination and another which is incomplete.   Although the ratio is never constant,  both a fully terminated pyramid and a truncated pyramid are usually present in Wurtzite from this locality.   Crystals do occur, however, for which this last statement is untrue and only one pyrimid develops.                                                                                                                       Wurtzite Crystal Systems

Habit         Wurtzite crystals generally develop in three different habits in the Negley Septaria; well formed single crystals, radiating clusters, and non radiating crystal clusters.     In each case, crystals are generally well formed with crystal face striations perpendicular to crystal growth.  Often septaria with greater concentrations of Wurtzite will produce crystals in all three typical habits.  Very rarely, crystals will form acicular rods or free standing fans, but neither are usually well developed.   Single Crystals        Single Wurtzite crystals typically measure 1 millimeter or less.  Less commonly single crystals can measure upwards of 2 millimeters.   Over 90 percent of all single crystals develop with one or more faces attached to the matrix(parallel growth).  Of the crystals which grow away from the matrix, most will grow with the truncated pyramid attached to the matrix(base to tip growth).   Very rarely crystals grow in reverse with the fully terminated pyramid attached to the matrix(tip to base growth).  The rarity of this occurrence combined with the brittle nature of such crystal growth makes trimming such a specimen improbable. Wurtzite....Negley, Ohio (ditrigonal pyramidal crystal)

Radiating Wurtzite        Radiating crystal groups of Wurtzite occur prevalently in septaria from Negley.    As a rule, Wurtzite in this habit are produced by multiple crystals simultaneously growing away from a single point and can occur in a plane or at an angle.   Often, crystals in these radiating groups are of different size, pyramidal proportion and color.    It is also  Radiating Wurtzite Group....Negley, Ohio important to note that these groups frequently do not form perfect radials.   A radiating group may consist of no more than 2 or 3 crystals and only form a small percentage of the radial.   Classically, Wurtzite radials occur in a plane and are flush with the matrix.  Uncommonly, radiating crystal groups will develop perpendicular to the matrix and can be mistakenly identified as free-standing fans.  However, Wurtzite fans are typically flattened and seldom show evidence of pyramidal growth.   Individual crystals of Wurtzite are clearly visible in radiating crystal groups.  (note: radial is complete)

Radiating Wurtzite Group....Negley, Ohio (note: radial is incomplete)

Wurtzite Cluster....Negley, Ohio (note: growth striations, which are perpendicular to the crystal faces and a notch mutation, are  clearly visible in the upper left crystal)

Wurtzite Clusters       Wurtzite crystal clusters(non-radiating) occur in the septaria at Negley usually, but not always, in combination with radiating crystal groups and single crystals.  This habit is caused by single crystal growth occurring in close proximity, but not from the same source as in radiating crystal groups.   This allows the crystals to grow into each other instead of away from a single point forming clusters.   When single crystals develop in this way, many unusual and curious growth characteristics can be observed.   A typical cluster showing both radiating and non radiating crystals is pictured to the left.   Notice the upper crystal has grown towards the face of the largest crystal instead of away from the focus of the radiating pair.   The photo to the right shows several unusual facets of crystal growth.  First, what looks like a twinned crystal is more likely a product of two separate crystals, which at one point were unrelated, having grown together.   Although the photo does not clearly portray the development, the two crystals have actually grown at a 30 degree angle.  In addition, the right crystal is curving toward the viewer and the left crystal curving away.   Also, note the "twins" are a second generation growth on a larger 1st generation crystal showing heavy internal fracturing.  Finally, and most importantly, the crystals displayed in this picture are fully terminated hexagonal prisms without truncated counterparts.  Wurtzite Cluster....Negley, Ohio (note:an axis mutation and a hollow appearance in the base of  the "twinned"  crystals)

Hexagonal and Trigonal Pyramidal Wurtzite       As mentioned earlier, Wurtzite crystals generally will develop two pyramids; a fully terminated pyramid and a truncated pyramid.   Often, dihexagonal pyramidal crystals with one very short truncated pyramid will be misidentified as being hexagonal pyramidal.  The photo to the left  illustrates this phenomenon.    If only one pyramid is present it will typically be a fully terminated pyramid.  Also, the base of a true hexagonal pyramidal Wurtzite crystal will appear to be hollow.  Occasionally, a dihexagonal or ditrigonal crystal will develop with its fully terminated pyramid attached to the matrix.  After full growth is completed, the crystal may no longer have a fully terminated pyramid or may only display one pyramid which can cause the crystal to appear as a truncated hexagonal pyramid.  Dihexagonal pyramidal Wurtzite    Negley, Ohio (thin truncated pyramid on top)

Hexagonal pyramidal Wurtzite crystal....Negley, Ohio (no truncated pyramid present)

Wurtzite Crystal Mutations

After careful study of Wurtzite crystals found in the septaria at Negley, several different mutations can be readily identified.   The most typical mutations are illustrated in the figure to the right.  Mutations occur in both trigonal and hexagonal crystal systems and can be observed in several habits.  Notch mutations(1) are a most common occurrence in Wurtzite from this locality.  Crystals displaying this mutation appear to have had a stunted growth, meaning that crystal development stopped and then was later resumed resulting in an indentation parallel to the striations on the pyramid faces.   A rounded or teardrop mutation(2) can occur in dihexagonal and ditrigonal pyramidal crystals.  In this mutation the crystal faces of both pyramids are curved, but the axis

remains similar to a normal Wurtzite crystal.  A similar sloped or horn mutation(3) can occur in hexagonal and trigonal crystals.  In a horn mutation, the axis again remains typical, but crystal faces curve outward towards the base.  In the teardrop mutation, the crystal faces begin to curve outward away from the termination, but then curve inwards towards the base.  When the crystal axis is curved, an axis mutation(4) is formed.  In this mutation, the crystal faces are curved to accommodate the curved crystal axis resulting in a bent crystal.  It is not uncommon for a crystal to display more than one mutation.
 

Acicular Wurtzite........Negley, Ohio

Acicular Wurtzite      Of all the Wurtzite specimens locked inside the septaria at Negley, acicular crystals are by far the most difficult to locate and properly trim.  This is caused, primarily, by the fact that acicular Wurtzite is exceedingly rare.  In addition, the needle like crystal shape, along with the brittle nature of Wurtzite, leaves most acicular crystals in a fragile state.   Finally, the largest acicular crystals rarely reach much more than .4 millimeter in length.   All of these factors make micro mounting an acicular Wurtzite crystal unlikely.  The photo below shows an acicular Wurtzite crystal which developed out of an angled radiating group.   The crystal is hexagonal in nature and has grown away from the focus of the radial.   The crystals in the radiating group formed at an unusually steep angle creating a "cone" of radiating Wurtzite crystals.  It seems possible that the steep angle formed by the radiating group spawned the acicular crystal.

Collecting Status     Septaria and concretions are abundant and can be easily collected off the shale spoil piles around the open cuts and pits at Negley.  The photo to the right shows a typical quantity of concretions in shale at Negley.  A bucket, rock hammer, and hand lens are necessary for collecting.  Since the percentage of concretions with wurtzite is low, it is wise to break open the nodules and cull only those with wide shrinkage cracks.  A quick rinse in water will remove the clay which develops in the shrinkage cracks concealing the minute crystals.  While collecting, a quick puff of air can help to remove some of this for examination, but a light rinse will more thoroughly expose the crystals.   For further information and a more detailed analysis on the occurrence of Wurtzite in Ohio, read the Hollenbaugh and Carlson article listed in the references.

Wurtzite bearing concretions in shale....Negley, Ohio

  This article in no way grants the reader permission to collect on the dumps at Negley.  Permission must be obtained before collecting on any posted private property.
 
 

References Carlson E.H., 1991, Minerals of Ohio: Ohio Division of Geological Survey, p       18-20, 144 Hollenbaugh, D.W., and Carlson, E.H., 1983, The occurrence of Wurtzite       polytypes in eastern Ohio: Canadian Mineralogist, v. 21, p. 697-703 Korbel, P. and Novak, M., 1999, Minerals Encycolpedia, Rebo International,       p.30 Stout, W. E., and Lamborne, R.E., 1924, Geology of Columbiana County:       Ohio Division of Geological Survey Bulletin 28, 408p Stout, W.E., Stull, R.T., and McCaughey, WM. J., 1923, Coal Formation       Clays, Ohio Division of Geological Survey Bulletin 26, 588p Seaman, D.M., 1977, Wurtzite locality revisited.  Earth Science p.30, 181-183 Wolfe, M.E., 1997, Report on Ohio Mineral Industries, Ohio Division of       Geological Survey 130p

Wurtzite....Negley, Ohio

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