FMF - Friends of Minerals Forum, discussion and message board

[Roger Warin]

Calcite specimen for Textbooks.
Exceptionally rare Calcite crystal, extracted from the Rhisnes quarry, Namur (Belgium). It’s the type locality of this habit:
Dipyramidal hexagonal {8.8.-16.3} usually dominant.
Also reported from Kelley’s Island, Ohio, by Dana.

[arturo shaw]

(Hummm, that's Valere territory... )

It is extremely rare to see calcites from that place and this one is amazing.

Congratulations!

You could add the picture to Mindat, I cannot say there is a good representation there :-)

Thank you

Arturo

[Roger Warin]

Excellent hexagonal dipyramidal calcite were found in the USA. Do you have photos and some informations? Thank you.
Roger.

[arturo shaw]

Nope... It is easy not to appreciate the difference with some scalenohedrons, sometimes you have to measure the angles.

I have made two drawings, first with the {8 8 3} form and second including forms {221} and {111}.

In your specimen it is quite clear but in many other....

Thank you for sharing

Arturo

[Pete Richards]

Arturo, I think you mean hexagonal bipyramids not scalenohedra - at least all the forms you drew are hexagonal bipyramids.

Hexagonal bipyramids are the typical form not only at Kelley's Island, as Roger points out, but at a number of other localities in northwest Ohio. I have measured a number of them, and the form is always {8 8 -16 3}. But some have curved faces that become less steep towards the ends. These usually are not measurable because of the curved surface, but they appear to be scalenohedra at the ends merging into hexagonal bipyramids at the middle.

[arturo shaw]

Sure, thank you.

All those are bipyramids. What I mean is that the angle between some bipyramids and the scalenohedral face (like 221) can be almost imperceptible. I believe (and that is a personal opinion) that those roundish surfaces are made of a series of faces with increasing miller indices and very tiny angle changes. I find difficult to know (without measuring) when those faces are bipyramids or scalenohedrons, especially if I can't see the hexagon at the base of the bipyramids.

I believe that many pyramidal calcite and some locations are not properly known because of that reason. And I don't mean your calcites, Pete, but those belonging to humble collectors like myself.

Thanks

Arturo

[Pete Richards]

[arturo shaw]

Pete, it is always a pleasure to learn from you.

Thank you

Arturo

[Roger Warin]

Wow, you're interested. I will continue to talk a little about hexagonal calcite, in addition to the pertinent Pete's words.
First precision, in my example, there is no twin on {00.1}. This is one "pure" form which gives this hexagonal dipyramid.
For scalenohedra, the equatorial contour is a zigzag, while in the hexagonal dipyramid, the equator is a straight line in a plane.
Calcite can be modified by more than 250 different theoretical crystallographic forms (such as rhombohedra, base, scalenohedra, etc.), These forms do produce an infinite number of aspects of calcite crystals. Of all these forms the hexagonal dipyramid {88.3} can be found, but the general appearanceof calcite is not changed so much.
What is exceptional in Rhisnes Quarry, it is almost unique presence of this exotic form. The termination is formed by the faces of the primitive rhombohedron, as shown in the drawing.
The absence of twinning on {00.1} (in the midplane) is seen by the direction of the cleavage planes. There are the same in the upper and in the lower part.
A twin does also influence crystal terminations.
Roger.

[Roger Warin]

All known calcites of Rhisnes Quarry were found between 1890 - 1900 by Giuseppe Cesàro, professor at the Liège University.
Captivated by this great scientist, with two friends we explored again this career to research these mythical calcites. And we found some. Wowww.
That was in 1992. We were lucky because due to a severe drought, the ground water has dropped, reducing the water level in the flooded quarry. The economy was good in those days and Kraft plant adjacent to the site sucked a lot of water in the aquifer. So we could walk on a flooded level for 100 years.
Some good specimens have been found, including one in the photo.
Rhisnes Quarry is also typical of other features. As well hydrothermal attack highlighted the primer cleavage planes in corroding these tracks.
In addition, secondary crystals (without hexagonal bipyramid) are frequent. They are not arbitrary, but arise in parallel growth on initial bipyramid. They are placed on the end, covering the crystal. Or they include the equator of the crystal.
They are indeed parallel growth (crystal axes parallel to the first crystal). The alignment of the cleavage planes proves it.
Roger.

[Roger Warin]

Hi,
About the hexagonal dipyramidal {88.3} calcite from Rhisnes, Belgium.
Cesàro discovered dipyramidal calcite in Rhisnes Quarry around 1885-1890. His colleague and friend A. Lacroix found the find so interesting that he includes a description of this very rare form in his book "Mineralogy of France." This crystallization has become a classic example of the hexagonal dipyramide {88.3}.
This quarry supplied limestone to lime kilns. It was abandoned in the early 20th century. It was quickly flooded, and also the contiguous career of black marble.
These dipyramidal calcites are so exhausted and inaccessible in the interesting area.
In 1992, however, a drought associated with significant pumping of groundwater by neighboring Kraft factory, decreased the water level.
Having been on the site, I witnessed the discovery of this sample by my friend Michel Houssa. This specimen is not as corroded as those collected by Cesaro a century earlier, because it was totally stuck in clay. He also wears crystallization with parallel axes, classic shapes, but secondary parallel growths of Cesàro’s crystals were different.
So all hope is not lost to rediscover a mineral in an abandoned site.
Roger.