This site was last updated on June, 2010
Quartz Crystal Habits within Herkimer Diamond Deposits
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Larger photos of the thumbnails presented on the main "Crystal Form" page. Included is identification information and the source link is embedded there (just click). In some cases additional information and comments are provided for each photo.
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Skeletal & Hopper Crystals and Their Features
From the collection of Jeff and Val Collins
An excellent group of skeletal crystals, the top crystal shows what looks like a "hole" (arrow). This an incomplete face of a skeletal cyrstal exposing it's "skeleton". Under most of the clear flat faces you would see the skelton (see photo on the right).
This is an excellent picture of a skeletal crystal where you can see the concentric lines mimicing the edges of the crystal face, yet hidden under a flat smooth clear surface. There is also a small hole where the flat face did not completely heal over. This is what is on the top crystal in the picture to the right. One of the reasons that these skeletal features can be seen well in this crystal is that they have a cream/tan clay coating on some of the skeletal features (see photos below). A close up is shown below.
New York State Museum Specimen
New York State Museum Specimen
Although the distinction between the terms "skeletal" crystal and "hopper" crystal can be overlapping, the photo on the left is of a hopper crystal. With some examination the viewer should see that there are not well developed flat faces. In the places where the faces are supposed to be is crystal development in a step like, almost blocky, pattern. When the flat faces of the crystal are more than 50% absent and replaced by step like growth the term hopper could be used. Hopper crystals are rare in the Herkimer district. Skeletal crystals (where you can see the layers under the complete or nearly complete flat faces) are more common. Each hopper crystal is slightly individual in form, but they tell their own story about the formation of Herkimer diamonds.
Hopper crystals from the Herkimer mining district almost alway have some interesting testures or patterns somewhere on the crystal. The above photos show the most common feature - the step like pattern down the face of the crystal, toward the middle.
Below (left) is a regular camera photo from the above hopper crystal showing "pine tree" melting/healing texture textures, sort of what it looks like to the naked eye. Second to the step like pattern the "pine tree" texture is the most common texture seen associated with skeletal and hopper crystals. The rainbow is due to a fracture under the texture that is refracting light. Below right is a microsope photo of "pine tree texture.
On the right is another hopper crystal (bordering on being a skeletal, and thus showing where it may be difficult to say when to use which term) where the interior pattern is not as "blocky" as one above, but more globular. Several other photos (see the artistic page, and also below) come from this specimen. This is from Middleville, NY. Photo by Dr.D. 2008
Sometimes skeletal crystals are called "elestial" referring to metaphysical properties
<- clay coating
A thought to ponder upon - It seems that pockets containing well developed skeletal and hopper crystals have more clay that is lighter in color, having less hydrocarbon (but not zero). This is opposite to the clear crystal pockets which are filled with black hydrocarbon material and nick named "jewlery boxes". Given that this is generallly true, then this has something to say about the formation of Herkimer diamonds. This idea is open for critical input from the public - just send an email.
A public service project always open to input from the community interested in Herkimer diamonds.
Web page author - W. David Hoisington, Ph.D.
to the left is the triangular termination face of a crystal that shows the step like pattern of skeletal growth along with the pale clay coating. This specimen is from TCR and is about 3 cm across. Photo DrD, 2009
Using either the term skeletal crystal or hopper crystal
The photo to the right shows what the "pine tree" texture looks like close up. It is 5 mm across and from TCR. Photo DrD, 2009.
Look at your Herkimer collection - do you have skeletal or hopper crystals? Do they have interesting textures? Check out the artisitc page for more texture photos.
Just to help with clarification, I propose that we use two different terms for describing these unique Herkimer diamonds - skeletal crystals, that have more than 50% of their surface face covering the step like pattern inside the crystal, and hopper crystals where more than 50% of the step like pattern is open and exposed. What is important is that with a skeletal most of the step pattern is inside the crystal and with a hopper most of it is exposed. The term "elestial" should not be used.
Skeletal and hopper crystals have something important to say about the history of Herkimer diamonds.
Thus far, every deposit in the Herkimer mining district has either skeletal or hopper crystals, or both. This means that the conditions for making such crystals is a feature consistant across the district, much in the same way the the black carbon and material baby floater druze is consistent across the district. And both are directly related to developing a reasonable history explaining the development of Herkimer diamonds.
The best way to think about hopper/skeletal crystals is to think about crystals being "forced" to grow very rapidly. This can happen when the solution is supersaturated, meaning it has alot of quartz disolved in it. What then happens is that the edges of the crystals grow faster then the faces, giving you this step like "skeleton". But the solution is not continually stable so we get face development alternating with edge development and sometimes the face development wins and the outside of the crystal is formed over the top of an "inside skelton". This fluctuating, unstable, nature of the fluid is also important in terms of understanding how clear Herkimer diamonds happen (see the FAQ) page. There was a dynamic interplay in the Herkimer district between the following conditions: 1) the saturation of the mineral forming solutions, 2) the space available to grow, and 3) the amount of oil/gas present and its timing in connection to the mineral bearing fluids.
We also know from field evidence that there was a late Herkimer "healing" quartz event. There are fractured Herkimer diamonds that are totally "healed" (see the inclusions page). Some of the skeletal crystal features may be the result of this process (a hopper crystal that was healed), but there is still more research that needs to be done. 2009 field work at TCR suggests that when the later quartz healing event encountered a hopper crystal that it tended to form multiple parallel growth crystals over the earlier hopper as the solution strugles to decide which surfaces to actually grow from. A photo of this "skeletal/hopper parallel growth" is shown below (although better examples exist, and could be photographed).
The specimen to the left shows the parallel growth at the top where you have the crystals points (see the pink arrows) mimicing each other and the faces overlapping. This specimen, donated by the TCR mine owner, was in fragments and then reconstructed. It measures 10 cm across (photo Dr. D., 2010).
The specimen below shows another feature that may be unique to the TCR location - white solid Herkimer diamonds as the core for growing a skeletal/hopper. This specimen, was donated by the mine owner, measures 10 cm across (photo Dr. D., 2010).
The photo is of the bottom of a crystal. Note the hexagonal shaped hole. Here sat a white Herkimer diamond. Note also the step like growth pattern concentric around the hole.
What does the information from these specimens tell us?
The first thing is that we might need to pay more careful attention to the growth patterns associated with hopper crystals from all the deposits. Do any of the other deposits show these features described above? Do they show features unique to only that deposit?
It is to early to say that the TCR location is the only deposit to display these features.
Hole where core Herkimer diamond used to be located
The specimen to the left shows another feature that may be unique to the TCR location - clear, gemmy, step hopper growth. The growth often has a light smoky color. This specimen, damaged, was donated by the mine owner, measures 10 cm top to bottom (photo Dr. D., 2009).
Hopper crystal textures and patterns
After the step pattern (which can be seen in the photo on the left as big arched steps on the lower left and also a series of lines in the upper right) and the "pine tree" texture (shown int the above photos), the third most common texture is "scalloped etching".
The photo, taken with a macro lens, is 4 cm across and from TCR (donated by the mine owner). Arrow points to the scalloped etching. Photo DrD, 2010.
Sometimes you don't need fully developed hopper patterns to find interesting textures. You just need to turn the crystal into the sunlight at just the right angle. The photo below is of a double terminated crystal that is more skeletal (step features are inside the crystal) than hopper and has a pair of crystals attached. It is 10 cm long collected with permission from TCR. The unusual texture, center bottom, looks "ghostly", like it was spray painted on to the crystal. To the touch it is a very fine feature (not much relief). Photo DrD, 2010.