Epitaxial Growth       Epitaxially grown dolomite and ferroan dolomite crystals can regularly be found throughout western Ohio.  However, they are not common at the Monroeville locality.  This habit has been positively identified only in the first four generations of ferroan dolomite growth.  Epitaxially grown crystals are more common in the honeycomb-like boxwork of the 2nd generation.  It is possible that this habit exists in the 5th and 6th generations as well but is masked by the advanced curvature of crystals from those generations.  Epitaxial growth is best described as a network of individual crystals that have the same orientation as if grown face to face.  This habit is easily identified when light sweeps across the crystal faces revealing the parallel growth.  The majority of crystals that display this habit are less than 3 mm in size, though much larger examples from the 3rd generation have also been observed.  Epitaxial growth has been observed in crystals lining small pockets and as stalactitic chains of crystals that grow across small pockets.  In the photo to the right, a typical example of epitaxially grown crystals lining a small boxwork pocket is displayed.  Due to the fact that dolomite crystals have tendency to curve, these crystals are not perfectly parallel, however the vast majority of the crystals on the left side of the pocket appear to be oriented in the same direction.

epitaxially grown ferroan dolomite field of view is 9 mm x 6 mm West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

Multiple Step Growth Crystals      Ferroan dolomite crystals from this locality will occasionally show a multiple step growth habit.  This habit has been seen on both straight and curved crystals and is quite common in larger crystals from the 2nd generation.  Large plates of crystals showing this habit make for very attractive specimens.   Crystals showing this habit appear to be an assemblage of smaller, epitaxially grown, “building block” rhombohedrons.  Composite crystals up to 2 cm have been  curved step growth rhombohedron  crystal measures 1.2 cm West branch of the Huron River  at Lamereaux road bridge Monroeville, Huron Co., Ohio observed.  Rarely, a series of these larger rhombohedrons will also be epitaxially grown togetherbut this is not the norm.  Smaller crystals from other generations will also display the multiple step growth habit, but are generally not as well developed and show far fewer steps.  In general, this habit is more easily identified in sharper crystals such as those pictured to the left and right.  In the photo to the left, an example of a multiple step growth curved rhombohedron is displayed.  Notice how the numerous steps distort and disguise the larger rhombohedral shape.  The photo to the right displays a cluster of straight multiple step growth rhombohedrons.   The larger rhombohedral shape of the crystals is slightly more identifiable on this specimen, because the steps are thinner.

straight step growth rhombohedrons field of view is 5.0 cm by 3.6 cm West branch of the Huron River  at Lamereaux road bridge Monroeville, Huron Co., Ohio

twinned ferroan dolomite crystals largest crystal measures 5 mm West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

Twinned Ferroan Dolomite        Twinned crystals of ferroan dolomite are observed with some frequency at the Monroeville locality.  The majority of twinned crystals are curved saddle-shaped crystals, which form small flower-like crystal groups as previously described.  Intergrown or penetration twins of simple rhombohedrons are also occasionallyencountered.   Penetration twins are two crystals which develop simultaneously and pass through each other along a twinning plane.  This type of twinning occurs most commonly in the first three generations of ferroan dolomite growth.  The photo to the left displays penetration twins from the 2nd generation.  Often, this type of twinning is still evident after 4th generation growth.   An example of several twinned crystals coated with tiny, light gray, 4th generation crystals is displayed in the photo to the right. twinned crystals coated with 4th generation Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

4th Generation Ferroan Dolomite Growth      The 4th generation is unique in that it varies in levels of completeness.  In general, the first three generations are either present or not.  The fifth generation, when present, is typically made up of individuals, groups, or occasional thick crusts of large curved crystals.  The 4th generation is made up of varying amounts of tiny multiple growth,  4th generation coating earlier crystal crystal measures 1.2 cm West branch of the Huron River  at Lamereaux road bridge Monroeville, Huron Co., Ohio   4th generation coating earlier crystal crystal measures 1.7 cm West branch of the Huron River  at Lamereaux road bridge Monroeville, Huron Co., Ohio epitaxially grown rhombohedrons with curved faces that coat earlier generations.  The photo to the upper right clearly exhibits the nature of the 4th generation.  In the far right side of this photo the 4th generation is not present on the black 3rd generation crystals.  Through the center of the photo a zone exists where a thin amount of the tan 4th generation has been deposited on the 3rd generation crystals.  This 4th generation is much thicker and more yellow towards the upper left part of the photo.  When fully developed, this generation will produce small oddly formed stalactites of dolomite crystals.  This generation varies in color from cream to light gray, tan, yellow, brown, orange, red and occasionally brownish black.  The photo to the upper left displays a 2nd generation crystal that has a very thin coating of the 4th generation crystals.  The crystal in the photo to the lower left has a thicker coating of 4th generation crystals.  The 4th generation crystals on this specimen have greater curvature, which created a rounder overall rhombohedral form and the development of multiple terminations.  The crystal in the photo to the lower right is heavily distorted by the growth of 4th generation crystals.  It is probable that a small 2nd or 3rd generation  crystal with negative rhombohedral modifications lies at the center of this form.  While important to the paragenesis of the locality, this generation of crystals is perhaps the least aesthetic.

specimen showing growth of the 4th generation field of view is 7.0 cm by 5.0 cm West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio distorted shape created by 4th generation growth crystal measures .8 cm West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

rounded rhombohedral dolomite crystals in pocket of ferroan dolomite (Specimen Joseph W. Vasichko) specimen measures 10.3 cm x 5.8 cm West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

Dolomite CaMg(CO3)2      Uncommon examples of relatively iron free dolomite crystals are occasionally observed in septaria at the Monroeville locality.  These milky white dolomite crystals developed after the 4th generation of ferroan dolomite and are of similar form to 5th generation ferroan dolomite; large curved rhombohedrons, rounded rhombohedrons or stacked rhombohedrons.  There are two theories as to how these crystals developed.  The first is that these dolomite crystals developed  simultaneously with or in place of the 5th generation of ferroan dolomite.  However, the similarity in form suggests the possibility that the entire 5th generation began as dolomite and later altered to ferroan dolomite.  In either case, very few actual dolomite crystals exist at the locality.  Only those crystals that are purely white in color or are white when broken should be considered dolomite.  All others are more likely ferroan dolomite.  The photos to the left and right display common examples of dolomite crystals from this locality.  curved dolomite crystals  crystal measures 1.2 cm West Branch of the Huron River  at Lamereaux Road Bridge Monroeville, Huron Co., Ohio

Quartz SiO2       The Huron River is one of the premier localities in Ohio for quartz specimens.  Although much larger drusy crystals occur at Flint Ridge in Muskingum County, specimens of quartz crystals in combination with ferroan dolomite and other septarian minerals from the Huron River are far more attractive.  In fact, the sharpest individuals compare favorably with specimens of Herkimer Diamonds from Middleville, New York.   Equally impressive are specimens of multigrowth flower quartz in combination with 2nd generation ferroan dolomite.  A number of habits of water clear, milky and smoky quartz occur at the Monroeville locality.  Some of the more common habits found at the locality are drusy quartz, multigrowth flower quartz, doubly terminated diamonds, pseudo-cubical quartz and chalcedony.  Masses and thick seams of milky gray, drusy quartz points are more common than large individual crystals.  Distorted crystals occur more regularly than crystals of perfect form.  A few crystals with indistinct and distorted smoky or milky phantoms have also been observed.  Individual quartz crystals range from microscopic to 3 centimeters in size.  Quartz crystals from this locality occasionally have inclusions of other minerals, especially marcasite and pyrite.  Dissolution of these iron sulfides causes light to moderate amounts of yellowish iron staining on some quartz specimens.

smoky quartz crystal on ferroan dolomite (specimen Joseph W. Vasichko) crystal measures 1.2 cm  West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

water clear quartz crystal on ferroan dolomite (specimen Joseph W. Vasichko) crystal measures .5 cm  West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

Quartz Occurrence      At least three distinct generations of quartz are present at the Monroeville locality.  Each of these generations is unique and easily distinguished from the other two.  The very rarely seen first generation of quartz occurred between the 2nd and 3rd generations of ferroan dolomite.  This generation produced snow white botryoidal chalcedony which is generally coated with second generation drusy quartz crystals.  The 2nd and 3rd quartz generations produced well-formed crystals of dissimilar form.  The more common 2nd generation of quartz occurred before the 3rd generation of ferroan dolomite.  This generation typically formed individuals, small groups, drusy crusts or thick seams of partially clouded multigrowth crystals.  The 3rd generation of quartz occurred between the fourth and fifth generations of ferroan dolomite.  This generation of quartz forms beautiful individuals and groups of diamond like crystals that range from water clear to deep smoky black.  An example of a 3rd generation diamond like crystal is displayed in the photo to the left.   Since quartz does not occur as commonly as ferroan dolomite at this locality, and since two generations of ferroan dolomite occur between the crystalline quartz generations, specimens showing crystals from both of these later quartz generations are exceedingly rare.

Quartz Crystal Forms       The Monroeville locality is one of the few Ohio localities that produce numerous crystal forms and habits of quartz.  In all, six crystal forms have been observed at this locality.  The most common of these forms are labeled A, B and C in figure III to the right.  Crystal A describes the basic form; an hexagonal prism(m) in combination with positive rhombohedron(r) and negative rhombohedron(z).  Although rarely as doubly terminated crystals, this form is employed by most 2nd generation crystals.  Crystal B has the same basic form, but the prism faces are very small in comparison to the terminal rhombohedral faces.  This is very common in 3rd generation quartz crystals.  Some or all of the prism faces are occasionally absent in 3rd generation crystals as illustrated by crystal C.  Pseudo-cubical quartz crystals have also been observed in the 3rd generation.  This crystal form, illustrated by crystal D, is similar to crystal C, except that the positive rhombohedron is far greater in size than the negative rhombohedron.  The prism faces may or may not be present on this form.  A few examples of crystals with a second order prism face(a), labeled E in figure III, were also observed.  This modification was found only on 2nd generation crystals.  Rare trigonal pyramid faces (s), as described by crystal F, were also seen on crystals from the second generation.

Fig III.  forms of quartz crystals from septaria at the Lamereaux road  bridge locality.  A) basic form, positive(r) and negative(z) rhombohedrons  with hexagonal prism (m),  B) slight prism, C) prism faces absent,  D) pseudo cubic, E) basic form with second order prism face(a), F) basic  form with rare trigonal pyramid face(s).

Basic Crystal Form       Quartz crystals from both the 2nd and 3rd generations have been observed with the basic quartz crystal form.  Although it is often masked by the habit of the crystal, this form is more common in 2nd generation crystals.  On the perfect crystal of this shape, the prism faces will be larger than the rhombohedral faces and the positive rhombohedral face will be slightly larger than the negative rhombohedral face.   A good example of this form is pictured to the upper left.  3rd generation quartz crystal crystal measures 4 mm West branch of the Huron River  at Lamereaux road bridge Monroeville, Huron Co., Ohio     3rd generation quartz crystal crystal measures 5 mm West branch of the Huron River  at Lamereaux road bridge Monroeville, Huron Co., Ohio This crystal from the 3rd generation is much sharper and of clearer form than crystals from the 2nd generation.  An example of this form from the 2nd  generation is displayed in the photo to the upper right.  As is common, the prism faces are less distinct on this crystal than on crystals from the 3rd generation.   The prism faces of 3rd generation crystals are generally proportionally small in comparison to the rhombohedral faces, as illustrated by crystal B, in figure III.  This gives the crystal a more diamond like appearance.  An example is displayed in the photo to the lower left.   Prism faces are generally offset by the disproportion of the positive and negative rhombohedral faces.   This is far more noticeable on crystals with shortened prism faces.  Additionally these faces will often be of dissimilar size due to varying amounts of rhombohedral distortion.  Rarely, some or all of the prism faces will be absent.  The picture to the lower right displays an example of this habit.  On this crystal two faces have been lit, a thin prism face and a rhombohedral face.  The prism face which should be adjacent to and below the lit rhombohedral face is absent on this crystal.  Crystals with all of the prism faces absent are less frequently observed.

2nd generation multiply terminated crystal on ferroan dolomite (specimen Joseph W. Vasichko) crystal measures 1.5 cm  West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio 3rd generation quartz crystal with absent prism faces (specimen Joseph W. Vasichko) crystal measures 9 mm  West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

quartz crystal with large y-axis distortion (specimen Joseph W. Vasichko) crystal measures 1.1 cm West branch of the Huron River at Lamereaux road bridge Monroeville, Huron Co., Ohio

Y-axis distortion       Many quartz crystals, especially larger crystals, will exhibit some type of distortion of the basic crystal form.  Although there are several types of distortion that occur at the locality, the most common occurs when the crystal is stretched along the y-axis.  This creates a broader and flatter crystal with an unusual termination.  The two prism faces parallel to the y-axis are much longer than the remaining prism faces.  Also, the rhombohedral faces above and below these two prism faces are equally stretched along the y-axis.  The distortion is most noticeable at the termination of the crystal where an apex is formed by the two stretched rhombohedral faces instead of a 3 or 6 sided pinnacle.   This apex is allowed to form, because the angle of the rhombohedral faces in relation to the prism faces remains constant and does not decrease to accommodate the expansion.   On quartz from the Monroeville locality, this type of distortion can be very slight to moderate.   However, rarely is the crystal longest along the y-axis.  The amount of distortion is best measured by the length of the apex termination.  The photo to the left displays a 3rd generation crystal with this type of distortion.  The y-axis distortion on this crystal is larger than average for the locality.  Crystals from both the 2nd and 3rd generations of quartz will show this distortion.

Pseudo-Cubical Quartz       One of the more unique crystal forms of quartz is the pseudo-cubical variety.   Pseudo cubical crystals are created by severe rhombohedral distortion and disproportion.  One rhombohedron is proportionally very large in comparison to the other.  Also, the prism faces are generally very small, incomplete or non existent as illustrated in fig IV to the lower left.  This form has been observed only in 3rd generation crystals.   Although large examples of these occur at several worldwide localities, most notably high temperature alpine deposits in Austria, pseudo cubic crystals at the Huron River are  fig IV. pseudo-cubical quartz forms: A) positive  rhombohedron(R) and smaller negative  rhombohedron(Z), B) with prism faces(M) generally less than 3 mm in size.   A typical example of this form is displayed in the photograph to the right.  Quartz crystals often show varying amounts of this distortion and only those that are severely distorted appear cubic.  Pseudo-cubic crystals are usually observed among regular diamond like 3rd generation crystals and are of similar color and clarity.

Pseudo-cubical quartz crystal with prism face  (specimen Joseph W. Vasichko) crystal measures 2 mm West Branch of the Huron River at Lamereaux Road Bridge Monroeville, Huron Co., Ohio