Ohio Rockhound       v.1   art. 6
Gypsum var. Selenite Crystals

from

Ellsworth, Mahoning Co., Ohio

by Joseph W. Vasichko
 

Introduction
  One of the oldest known, yet still productive, mineral localities in the state of Ohio is the Selenite crystal locality along the West Branch of Meander Creek, 1/3 mile Southeast of Ellsworth, Mahoning Co., Ohio.  Many would argue this to be one of the best world-wide localities for Gypsum crystals of this form.   Having been described on multiple occasions, as in Edward Salisbary Dana's original textbook of mineralogy, the locality has been famous for producing sharp, well formed Gypsum var. Selenite crystals for nearly 200 years.   However, despite being a world-known classic locality, the clay bank which forms these Selenite crystals is rarely visited by mineral collectors.  Several factors contribute to the lack of attention given this locality in recent years.  First, more easily accessible localities for similar crystals have been discovered in the last 50 years.  Second, this locality remains relatively elusive, having never been described with pinpoint directions to the exact location, leading some to believe that it is either closed or defunct.  Third, the muddy nature of the locality during the best collecting season is moderately uninviting.  Also, the locality is positioned on multiple properties and permission to collect is difficult to secure.  Finally, a general disregard among many collectors for common and colorless minerals has resulted in a lack of demand for quality specimens from the locality.  In recent years, only the most serious mineral collectors have any appreciation for these classic specimens.  However, it is the author's belief that the Ellsworth location remains the best Ohio locality for this crystal form of Gypsum. 

Gypsum var. Selenite crystals in clay matrix
lower crystal measures 2.3 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 

Soil slide revealing the Selenite crystal bearing clay bank
South side of the West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio (photo 2004)
History
  In 1821, the Ellsworth location was first noted by Benjamin Silliman in the American Journal of Science in an article on crystallized gypsum.   However, it is likely that the location was well known in the area for many years prior to that publication.  Since that time, the locality has been described on multiple occasions.   Perhaps the best of these descriptions appeared in Rocks and Minerals v.12, in 1937.  The article by Gerald Greene relays several important pieces of information about the locality.  His article speaks of a large group outing to the site and a conversation with one of the older residents of the area.  He relates the story that a bushel of perfect crystals were collected 50 years prior and sold for $40.00.  The more interesting fact in his story, geologically speaking, is that due to erosion and land use, the actual exposure of the clay had moved since its first discovery.  The place where the bushel of crystals had been collected was located approximately 100 feet from the locality he had visited in his collecting efforts.   The reason for this is evident.  As the stream slowly carves its way into the side of the hill, soil slides occur along the face of the clay bank revealing fresh clay.   Over time, these slides grow over with vegetation.   In fact, a conversation with one of the older landowners revealed that, at one time, the "crystal beds", as they are locally known, were revealed by as many as 6 slides in a 100 yard stretch of the creek.  However, there is currently only one large slide which reveals the clay bank.   With this in mind, it seems highly unlikely, that the current slide is in the exact location of the first discovery.

 
Geology 
     The area surrounding Ellsworth was once part of a Pleistocene lake, likely resulting from the retreat of the Wisconsinan glacier which covered much of Northern Ohio.  This lake deposited beds of clay, silt, and gravel.     Beneath these pleistocene deposits lie Pennsylvanian age shale and limestone beds.  A thin coal seam has been reported nearby, and is evidenced in the gravel bars of the West Branch of Meander Creek.  The crystal bearing clay is generally bluish gray, however at the surface it is partially mixed with soil and is lighter tan in color.  The actual bluish gray clay layer is soft and slightly moist.   It is also very compact, nearly water tight and generally difficult to dig through.   If not for small sediments and vegetation, the clay would be very suitable for sculpture or pottery.   In the photo to the right, the thickness and tenacity of the clay are evident by a small hole, less than 50 cm across and 30 cm deep, which was dug for Selenite crystals.  More than one hour was required to carefully dig this small hole with a rock pick.  However, this one area yielded several sharp Selenite crystals.   Notice the clear pick marks remaining from working the stiff clay. 

Small hole dug for Selenite crystals in the clay bank
South side of the West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 
Mineralogy
    The only mineral at this locality of interest to collectors is Gypsum.  However, there are a few other minerals in the area which possibly led to the creation of the Selenite crystals.   First, small amounts of Pyrite have been reported from the shale beds surrounding the coal.  This is possibly the origin of the Sulfur for the Gypsum crystals.  Small amounts of Limestone above the shale are theoretically the source of the Calcium.  It has been hypothesized that ground water movement along with seasonal evaporation formed the crystals.  In addition, it is believed that these crystals are still forming in the clay.  In fact, in dryer times of the year, the gypsum crystals appear to be sharper and larger.    It is not clear whether the Gypsum crystals can grow from Calcium and Sulfur ions already in the clay or only through hydration and evaporation of local ground water.   An attempt to prove this by growing crystals in clay removed from the locality has thus far been inconclusive.  Siderite concretions containing Sphalerite, Barite and Calcite have also been reported and observed in the vicinity of this locality.  It is possible, that concretions containing the same minerals may occur in the shale beds beneath the clay at this locality.  However, these minerals only occur as small masses and are not of specimen quality.

Diagram of a soil slide exposing the Selenite bearing Clay 
West Branch of  Meander Creek
Ellsworth, Mahoning Co., Ohio

 
Gypsum var. Selenite CaSO4
     Selenite, a variety name applied to crystalline gypsum, is a fairly common sulfate mineral.  Several statewide localities have produced specimen quality examples of the species.  Although the average size of these crystals is generally smaller than those from some other statewide localities, the Ellsworth locality has been noted for producing some of the clearest and most well formed Selenite crystals in the state.   Selenite crystals from this locality range in size from less than 2 mm to nearly 6 cm.  Crystals of the larger size are extremely rare.  The average crystal is typically 1-2 cm in size.  Many of the crystals are grayish in color, having inclusions of the clay which helped form the crystals.  Occasional crystals will have included other small rocks from the clay.  Also, crystals attached to roots or other vegetation are not uncommon.  The most well formed crystals tend to develop in certain layers of the compact bluish gray clay, typically 4-8 inches beneath the surface.      However, it is important to note that there are several layers of the blue clay, and not all layers develop abundant Selenite crystals.  The reason for this remains unclear.  The clay which can be found at the surface is generally light tan in color and is mixed with soil.  Although often free of included sediment, Selenite crystals which form in this upper clay are typically rounded and corroded, possibly due to dissolution by rain water. 

Gypsum var. Selenite crystal in clay matrix,
crystal measures 3.4 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 
Common Ellsworth Selenite Crystal Forms
     At the Ellsworth locality, Selenite crystals have been observed in a few different habits, ranging from single crude or sharp crystals to twinned crystals and groups.  However, the basic crystal form exemplified by these crystals remains somewhat constant.   As illustrated in Figure I, to the right, Gypsum forms prismatic crystals in the monoclinic system.   While a few crystals from this locality will be true to form, most are somewhat distorted, with slightly to moderately unequal prismatic faces.   In this system, no crystal can be complete without the use of multiple crystal forms.  The most basic crystal form, labeled A, is comprised of four pairs of prismatic faces(2 pairs of macropism face (l) and two pairs of unit prism faces (m)), and one pair of clinopinacoid faces (b).  This 

Gypsum var. Selenite crystals 
larger crystal measures 2.9 cm
(specimen Joseph W. Vasichko)
clay bank along West Branch of 
Meander Creek
Ellsworth, Mahoning Co., Ohio
crystal form is dominated by the clinopinacoid face (b) and is always elongate along the macroprism face (l).  While this form is occasionally observed, the more common Selenite crystal observed at this locality is labeled B.   It is quite similar to the basic form, A, but slightly more complex with the addition of one pair of macrodome faces (e). The photo to the lower right displays a perfectly formed Selenite crystal without the Macrodome face (e). This macrodome face (e), which occurs perpendicular to face (m) is almost always rounded or rough and often concave.   On sharp crystals, the clinopinacoid face has distinct striations parallel to face (m).   Rare, crystals with multiple terminations have also been observed at this locality.  Typically, but not always, these occur when the crystal was forced to develop around rocks in the clay.  The crystal displayed in the photo to the left is an example of this.

Fig I.  Basic Gypsum crystal forms observed at Ellsworth
It is important to note, that most crystals observed at the locality are somewhat distorted, with unequal prismatic faces


Textbook Gypsum var. Selenite without macrodome face (e),
crystal measures 1.4 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio


 

Fig. II.  Three categories of Macrodome Development A) Deficient 
B) Ideal, C)Amplified
 

Gypsum crystal with Deficient
Macrodome face (e)
crystal measures 3.1 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of 
Meander Creek
Ellsworth, Mahoning Co., Ohio

Gypsum crystal with Amplified
Macrodome face (e
crystal measures 2.7 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of 
Meander Creek
Ellsworth, Mahoning Co., Ohio
Macrodome Face (e) Development
     Although the macrodome face (e), is always the most crude face on crystals from this locality, it is the only face which varies in proportion from crystal to crystal.  In fact, while the matching pairs of prismatic faces, (l) and (m), and clinopinacoid faces (b) may be nearly identical, the two macrodome faces (e) on any one crystal are often slightly different.  It is important to understand the three categories of development for the macrodome face (e), as illustrated in Figure II, to the upper left.   The size of the macrodome face (e) greatly changes the shape and appearance of Selenite crystals from this locality. The first degree is the Deficient form, labeled A.  Any crystal in which the macrodome face (e) does not connect with the clinopinacoid face (b) fits this category.  Notice that the macroprism face (l) clearly separates the macrodome face (e) from the clinopinacoid face (b).  Labeled B in Figure II., the Ideal category includes only those crystals where all four different faces of the crystal meet at one point.  As can be seen in crystal drawing B, faces (e),(l) and (b) meet at a single point.  The unit prism, face (m), also meets at this point.   This is the rarest single crystal to find at the locality.  The last category, Amplified, encompasses all crystals where the macrodome face (e) and the clinopinacoid face (b) join at a line.  This is the most common crystal form seen at the Ellsworth locality.  In this form, the macrodome is proportionally larger than either of the prism faces.  Also, the clinopinacoid face (b) is hexagonal in all crystals which exhibit this form.  No macrodome face (e) has been observed larger than 1/2 the size of the clinopinacoid face (b), in crystals from this locality.  Typically, the macrodome face (e) will be heavily clouded with sediment.  This feature is displayed in the photo to the near lower left. 

 
 Crowned Macrodome 
      As previously mentioned, the Macrodome is often concave, appearing as a slight to severe divot at the end of the adjoining macroprism faces (l).  Occasionally, the clinopinacoid face (b) along with the adjoining macroprisms (l)

Gypsum crystal with crowned
Macrodome face (e)
crystal measures 1.6 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of 
Meander Creek
Ellsworth, Mahoning Co., Ohio
will grow beyond the amplification of the  macrodome.  In this form, although the the macrodome face (e) is in an amplified state, it never joins the clinopinacoid face (b).  This form is commonly known as a crowned macrodome.  The termination of the resultant crystal forms the outline of a crown.   This crystal form is completely dominated by the clinopinacoid face (b).  This crowned form is exhibited in the the photo to the left.  The clinopinacoid face (b)  developed a 4 sided face despite the size of the amplified macrodome face (e).  The photo to the Right displays another similar macrodome and more clearly exhibits the resultant crown shape.

Gypsum crystal with crowned Macrodome face (e)
crystal width measures .8 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of  Meander Creek
Ellsworth, Mahoning Co., Ohio

 
Disproportionate Crystals
    While perfectly proportioned text book crystals are occasionally recovered, most crystals from this locality are slightly to moderately disproportionate.  There are two basic ways in which the crystal can be disproportionate.  The first is prismatic disproportion, labeled A in Figure III to the lower left..   This crystal imperfection occurs when the left and right prisms of the crystal are of unequal size.  On a perfect crystal, the left and right macroprism faces (l) and the left and right unit prism faces (m) should converge at a single point.  On crystals with this imperfection, these faces do not connect.  This disproportion is frequently seen in the macroprism faces (l).  Rare examples of disproportionate unit prism faces (m), have also been recovered from this locality.  The crystal in the photo to the right is an example of prismatic disproportion.   The second disproportion which is commonly seen in crystals from the Ellsworth locality is

Fig. III. Disproportionate Gypsum crystals A: prismatic
disproportion, B: macrodome disproportion.
macrodome disproportion.  This imperfection can be observed on most crystals from the locality and occurs when the macrodome face (e) is not symmetrical.  Occasionally, but not always, the macroprism faces (l) will be misshapen to accommodate the macrodome face (e) imperfection.  This has been illustrated in example B, Figure III.  Notice that the macrodome face (e) is not symmetrical and that the macroprism faces (l) have shifted to complete the crystal.  Other crystal flaws have been noted, but are not as common.

Disproportionate Gypsum crystal (prismatic)
crystal measures 2.6 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 

Backlit Selenite crystal with Growth Phantom
crystal measures 3.6 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio


Backlit Selenite crystal with hourglass Phantom
crystal measures 3.1 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

Phantom Selenite Crystals
     Perhaps the key to how Selenite develops at this locality can be found in the distinct phantoms which are common in these crystals.  Three classes of phantoms have been observed in crystals from the clay outcrops along Meander creek; growth, hourglass and planar.  The most common and revealing of these is the growth phantom.  Virtually all larger crystals will exhibit this phantom.  Its presence suggests that these crystals grew in multiple stages.   This phantom is generally identified as a series of crystal outlines created by included sediment or clay.  The photo to the upper left displays a classic example of this phantom.  Often, larger crystals will have 3 or more identifiable phantoms of this type.  It is also important to note that the 
smallest phantom in this crystal is sharper and truer to form than the crystal.  This leads to the conclusion that Selenite crystals, at this locality, become more and more imperfect as they grow larger.  The hourglass phantom is often more difficult to see in Selenite crystals from this locality.  Typically, it occurs as a faint outline of an X.  Under ultraviolet light, it is much more noticeable.  The photo to the lower left is a clear example of this phantom.  Planar phantoms occur along cleavage planes in the crystal.  Typically, these cracks are parallel to the clinopinacoid face (b).  These phantoms are irregular and look like a smeared oil stain inside the crystal.  The crystal in the photo to the right is a typical example of this.  Most crystals from the locality show this irregular phantom. 
Selenite crystal with Planar Phantom
crystal measures 3.3 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of 
Meander Creek
Ellsworth, Mahoning Co., Ohio
 

 
Selenite Fluorescence 
  As is common with many Ohio minerals, Selenite, from this locality, fluoresces a medium creamy green under both long and short wave ultraviolet light.  The fluorescence and strong phosphorescence of this mineral are similar to Travertine Calcite, Fluorite or Strontianite from Ohio.  This fluorescence is believed to be caused by slight amounts of petroleum in the crystal structure.  The classic fluorescence seen in most crystals from the locality is similar to an hourglass shape.  Some fluorescent references consider this an X-ray pattern or X-ray UV phantom.  However, due to the amount of sediment which is commonly found in these crystals, the X-ray pattern is often somewhat distorted or milky.  Also, the fluorescent portion of the crystal curves under the macrodome face (e).  This gives the hourglass shape a more curved or circular appearance.  In fact, the brightest fluorescent portion of the crystal is generally found just beneath the macrodome face.  On crystals without the macrodome face, the fluorescent portion of the crystal still behaves in this manner.  The picture to the right displays an Ellsworth Selenite crystal without a macrodome face.  Notice how the fluorescent portion curves away from the crystal's termination as if a macrodome were present.  Although it is far more pronounced in sharper Selenite crystals, this fluorescence has been observed in all crystals from this locality.  As is true for most petroleum activated minerals, the fluorescence is strongest under short wave ultra-violet light.

Selenite crystal under SW Ultraviolet light
crystal measures 2.9 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 

Selenite crystal group
large crystal measures 3.2 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio
Selenite Crystal Groups
     Small groups of Selenite crystals can also be found at the Ellsworth locality.   These typically occur when two or more crystals develop in close approximation and eventually  form a group.  However, due to the fact that crystals are generally small, less than
2 cm, and not abundant in the clay, groups of crystals are not common.   Because the crystals developed as individuals and were later joined, the size, proportion and overall form of grouped crystals are typically unrelated.  Crystals of equal size, proportion or form may be joined in a group, but the similarities are coincidental.   The photo to the left displays a typical crystal group.   The smaller crystal is not large enough to penetrate through the reverse side of the larger crystal.  The Selenite group pictured to the right consists of two similar sized crystals which do not intersect at either crystals center of growth.  A careful eye will also observe a third, smaller crystal projecting out of the intersection of the two larger crystals.
Selenite crystal group
crystal group measures 2.5 cm x 2.1 cm
(specimen John D. Vasichko)
Clay Bank along West Branch of  Meander Creek
Ellsworth, Mahoning Co., Ohio

 
Twinned Selenite Crystal Habits
    Although the Ellsworth locality is most famous for producing well formed single Selenite crystals, it also yields a variety of twinned crystals.  In general, Gypsum is best known for producing contact twins, such as a "fishtail" twin.  This type of twin occurs when the two halves of a twinned crystal are united by a twinning plane.  The resultant crystal forms a V-shape.  While this type of twin is commonly seen at several world-wide localities,  it has not been observed at the Ellsworth locality.   Crystals from this locality are more inclined to develop penetration twins.  A penetration twin occurs when the two halves of a twinned crystal intersect at a common center.  Generally, this is also the center of growth for both halves.  Typically, these twinned crystals will be of similar size, proportion and overall form.  Crystals which intersect at any other point, or are of unequal size are not considered to be twinned.  The figure to the right displays seven of the more common penetration twins which occur at the Ellsworth locality.  These forms can be separated into two distinct categories of penetration twins.  Crystals A, B, C and D in the illustration are classified as "Crossing" twins.  The last three crystals in the illustration, E,F and G, are categorized as Butterfly twins.  It is important to note, that twinned crystals from this locality are rarely of perfect proportion.  Also, it is not unusual for twinned crystals from this locality to show more than one twinning form. 

Fig. IV  Common Penetration Selenite Twins observed at Ellsworth: 
A) Parallel Pinwheel Cross, B) Parallel Symmetrical Cross, 
C) Intergrown Cross, D) Parallel Compound Symmetrical Cross, 
E) Incomplete Butterfly, F) Butterfly, G) Compound Butterfly

 

Twinned Gypsum var. Selenite crystal 
(Intergrown symmetrical Cross)
specimen measures 2.0 cm x 1.8
(specimen John D. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio


Twinned Gypsum var. Selenite crystal 
(parallel symmetrical Cross)
specimen measures 1.5 cm x 1.0 
(specimen John D. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

"Crossing" Selenite Twins
     The first category of twinned crystals, "Crossing" twins, encompasses all penetrating twins where the basic Selenite crystal shape is maintained by both crystals. For example, if one half of the twinned crystal were removed from the crystal in the photo to the upper left, the remaining twin would resemble any other Selenite crystal from the locality.  This can not be said for butterfly twins.  When discussing the different habits of crossing twins, it is first important to understand the difference between a pinwheel twin and a symmetrical twin.  This can be clearly observed in Figure IV. above.  A pinwheel twin occurs when both halves of the twinned crystal are facing the same direction, as in example A.   In contrast, a symmetrical twin occurs when the two halves of the twinned crystal are reversed, as in example B.  The latter of these two crystals forms a clear symmetrical X shape.  A true pinwheel twin is never symmetrical.  Parallel twins occur when the two halves of a twinned crystal have developed in parallel planes.  In General, crossing parallel twins are usually slightly offset.  The photo to the lower right exhibits a classic parallel pinwheel twin.  Notice that this crystal is in no way symmetrical.  Also, although the two halves of this twinned crystal developed in parallel planes, one of the twinned halves appears to be in front of the other.  Rarely, pinwheel twins of this type will also develop in the same plane.   This is not true for symmetrical twins.  If the two halves of a symmetrical penetrating twin occur in the same plane, a butterfly twin is always 
developed.   For instance, in the figure above, crystal B is similar to crystal F.    However, crystal B is offset and crystal F is planar.  The photo to the lower left is an example of a symmetrical crossing twin.   These are rarely encountered due to the fact that a butterfly twin is often formed even if the two halves of the twinned crystal are slightly offset.  One of the more interesting crossing twinned crystals to be recovered from the locality is the intergrown cross.  This type of twin occurs when the two halves of the twinned crystal share a common center, but are not parallel to one another.  Intergrown crossing twins may be pinwheel shaped or symmetrical, as pictured to the upper left.  The basic Selenite crystal form is more clearly identifiable in intergrown twins than in any other twinning habit. 
Twinned Gypsum var. Selenite crystal 
(parallel pinwheel Cross)
specimen measures 1.7 cm x 1.3
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 

Backlit twinned Selenite crystal 
(complete Butterfly Twin)
crystal measures 1.2 cm x .9 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio


Twinned Gypsum var. Selenite crystal in clay matrix
(Incomplete Butterfly Twin)
specimen measures 5.9 cm x 4.6 cm
(specimen John D. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

"Butterfly" Selenite Twins
    The most common twinned Selenite crystal found at the Ellsworth locality is the "butterfly" twin.  This type of twin occurs when the two halves of a symmetrical crystal develop in the same plane.  The butterfly twin takes on a completely different crystal form than that of the crossing twin.  In the butterfly twin, the terminations of the two halves have completely joined together, creating one large clinopinacoid face.   The resultant crystal resembles a pair hexagonal prisms joined by a "false" twinning plane. A small notch is created by the macropsims on each side of the false twinning plane.  The butterfly twinned crystal in the photo to the upper right is an example of this.  This 
Twinned Gypsum var. Selenite crystal in matrix
(Complete Butterfly Twin)
specimen measures 4.5 cm x 3.8 cm
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio
twinned crystal is also striated along the broad clinopinacoid faces perpendicular to the false twinning plane.  Striations of this type are common in sharper twins.  These striations are more clearly visible in the photo to the upper left.   An elongate and flattened macrodome face terminates each half of the twin.  As pictured to the upper left, an X shaped pattern of clay inclusions, can generally be found in butterfly twin Selenite crystals from the Ellsworth locality.   This X shaped pattern clearly indicates these to be penetrating twins.   Occasionally, and more commonly in corroded crystals, this pattern is visible on the surface of the clinopinacoid faces.  It is not uncommon for this type of twin to be incomplete.  In this case, only half of the twinned crystal will appear as a butterfly twin.  The crystal displayed in the photo to the lower left, is an exceptionally large and sharp example of this occurrence for the locality.   Notice that the lower half of the crystal resembles a single Selenite crystal, while the upper half has taken the form of a butterfly twin.  Nearly half of the twinned crystals from this locality will be incomplete in this manner.   This is also common in compound twinned crystals.  While crossing twins will exhibit a similar fluorescence to single crystals, complete butterfly twins are not as impressive under ultraviolet light.  A thin portion, directly beneath the elongate macrodome face is slightly fluorescent, but the classic hourglass patterns are no longer present.   This is not completely true for incomplete twins.  The incomplete half, which resembles a single crystal, will typically have the fluorescent hourglass pattern, while the completed half will not. 

 
Compound Selenite Twins
  There are many ways in which compound twinning occurs in Selenite from this locality.  A compound twin consists of more than two twinned halves.  Although this habit is far more common in butterfly twins, it has also been observed in crossing twins.   The most common way compound twinning occurs is through a series of planar twins.  A basic illustration on how this form of twinning occurs can be seen in figure V to the lower left.  In the illustration, each X shape represents one twinned pair of crystals.  In general, the additional twinned pairs are smaller in size than the central twin.   For instance, the crystal pictured to the left exhibits a compound butterfly twin.   Notice that the additional twinned pairs are smaller than the central twin.   In a regular butterfly twin, a notch was created by the macroprism on each side of the false twinning plane.  In compound butterfly twinned crystals, a series of notches representing the number of twins will be always be clearly

Figure V.  Planar compound butterfly twin
Each "X" represents one pair of twinned crystals.
visible.   The crystal to the right also exhibits a second set of butterfly twinned crystals which penetrate the planar twins.  Very few twinned crystals will show this form.  In all, this compound twin is comprised of 5 twinned pairs.  Other forms of compound twinning have been observed, but are too infrequent to mention. 

Twinned Gypsum var. Selenite crystal 
(compound Butterfly Twin)
specimen measures 2.6 cm x 1.5
(specimen John D. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 
Collecting Status
  Because the clay banks at the Ellsworth locality are continually growing new Selenite crystals, this locality will likely continue to produce specimens for many years to come.   Unfortunately, gaining access to the locality for future collecting is far more uncertain.  Currently, the clay bank locality is situated on property owned by two separate individuals.  A crude access road to the locality, is owned by a third individual.   Permission to cross and collect must be granted by all three landowners.  The information provided in this article is meant for locality reference only and not intended to be used as a guide for future collecting.  For this reason, contact information has not be provided in this article, nor will exact directions to the locality be revealed.   An approximate locality description can be found in the introduction.  In general, this locality is considered closed to collecting.  However, persons conducting research or collecting educational samples may be allowed to visit the locality.  Interested collectors should inquire locally for contact information.  Permission was obtained to visit and photograph the locality and collect a number of specimens for use in this article. 

Gypsum var. Selenite crystal in clay matrix
specimen measures 6.2 cm x 5.4
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio

 
Summary
  While other localities for Gypsum crystals exist throughout Northeast Ohio, the Ellsworth locality is perhaps the most recognized among world-wide collectors.  In part, this is due to the amount of written exposure the locality has received over the last 200 years.  Also, the Ellsworth locality produces top quality single and twinned Gypsum  crystals, which are among the sharpest, clearest and most well formed found in the state.  Furthermore, true mineral collectors appreciate the value of specimens from older and classic localities, even if the specimens are more recently collected.  It is important to note that the information in this article pertains specifically to the crystal habits observed at the Ellsworth locality.   Other nearby localities will produce similar and/or different habits of Gypsum var. Selenite crystals.  At this time, this collector would like to thank the property owners of the Ellsworth locality for their time and generosity.  This article would not have been possible without their support.  Their awareness of these unique crystals and willingness to allow specimens to be collected and preserved is greatly appreciated. 

Joseph W. Vasichko 
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio (photo 2004)

      This article in no way grants the reader permission to collect at the Ellsworth Selenite locality.   Permission must always be obtained before collecting on any private property.
 
 
References
Carlson E.H., 1991, Minerals of Ohio: Ohio Division of Geological Survey 
Carlson E.H., 2002, "Ohio Mineral locality Index, part 2: Concretions and
          Miscellaneous occurrences", Rocks and Minerals v. 77
Dana, E.S. and Ford, W.E., 1932, A textbook of Mineralogy( 4th ed.):New
          York, John Wiley and Sons 
Sinkankas, John, 1964, Mineralogy for Amateurs; Van Nostrand Company
          Inc.
Cleaveland, Parker, 1822, Treatise on Mineralogy and Geology(2nd Ed.);
          Boston, Cummings and Hilliard and Co.
Silliman, Benjamin, 1821, "Crystallized Gypsum" American Journal of 
          Science, v. 4
Greene, Gerald U. 1937, "Selenite Crystals at Ellsworth Ohio" Rocks and 
          Minerals v.12
Robinson, Samuel, 1825, Catalogue of American Minerals with their 
          localities; Boston, Cummings and Hilliard and Co.
Palache, C., H. Berman, and C. Frondel. 1951. The system of mineralogy. 
          7th ed., vol. 2. New York: John Wiley and Sons

Gypsum var. Selenite crystal in clay matrix
specimen measures 4.8 cm x 4.7
(specimen Joseph W. Vasichko)
Clay Bank along West Branch of Meander Creek
Ellsworth, Mahoning Co., Ohio