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[Roger Warin]

Giuseppe Raimondo Pio Cesàro
Naples 1849 - Comblain-au-Pont (Liège) 1939.

Cesaro was professor of crystallography and mathematics at the Liège University (Belgium) in 1895. He succeeded Gustave Dewalque.
He was also the tutor of mathematics of the future King Leopold III.
He was a friend of Alfred Lacroix (MNHN Paris), Georges Friedel (University of Strasbourg), vom Rath (University of Bonn) ...
He was a great crystallographer. He discovered (1887) the isocelohedron "L" (or hexagonal dipyramid) on calcite crystals of Rhisnes mine, very rare as dominant form for this mineral.
Roger.

[Jordi Fabre]

Dear Roger,

I love this thread as well as the other thread: Collection of H. UNGEMACH (1882 - 1936). You are doing a great job retrieving our patrimony, the mineralogical memory.

Please more!

[Roger Warin]

This message is especially for beginners.
Rhisnes is a magical place for the crystallographer. Fortunately, a great crystallographer, Cesàro, was present. Otherwise all these limestones have ended their lives in a lime kiln. This happened in the late 80s (in the 19th century).
Nature not only gave its hexagonal dipyramide in Rhisnes quarry but also several generations of growth have modified the crystals of calcite.
Thus, it is very often a second crystal grows on the first. While most of the time, this second crystallization is deposited randomly on the crystal, in this case, it is built on the foundations of the first. The plans of the Great Architect (Nature) have been met. In other words, the lattice remains unique. We have only one crystal. We say in this case that the growths are made along parallel axes.
Let us describe the specimen pic.
The primary crystal is a hexagonal dipyramid L {88.3}.
Then a second crystal is grafted. This one is a classic calcite composed of d2 {21.1} forms, i.e. the usual scalenohedron. This is modified by the e2 {10.0} prism, by the rhombohedron e3 {40.1} and also by L.
This photo shows a parallel growth.
Roger.

[Roger Warin]

About the second crystallization, we can see a Buttgenbach’s drawing of a similar calcite from Rhisnes, except that the form Φ {25 8 -25 3} is absent.
Ref.: H. Buttgenbach, Les Minéraux de Belgique et du Congo belge (1947).
When hexagonal dipyramids (as L) are secondary forms poorly marked, they are more difficult to identify without goniometric measurement.
Roger.

[Roger Warin]

This aesthetic group of calcite (Rhisnes) was studied by Cesàro.
You can admire the thoroughness of Cesàro, witness of a lost past.
A priori, this set is trivial, yet analysis yields amazing results.
It results from the assembly of three successive crystalline formations. A large variety crystallographic forms in calcite is possible.
Calcite is probably the mineral that can be modified by the largest number of forms. There are even exceptional Miller indices with values that appear in opposition to the rule of Miller’s rationality of indices.
PS: The letters correspond to the Haüy-Levy’s notation.
L : {8 8 . 3}
p : {10.1}
d2 : {21.1}
e3 : {40.1}
S’ : {19 10 . 6}
b5 : {41.6}
U’: {33 5 . 1}
u : {62.1}
u’ : {62.1}
The label is a report.
Roger.

[Martin Rich]

[Roger Warin]

Dear Martin
Of course the third indice is -28. My finger must have slipped on the numeric pad and as my sight is failing a bit, I have not seen this error.
Sorry for the mistake. Thank you for the report.
I like to illustrate by photos some basic facts that were taught to me at the university there very long.
As I have the opportunity to perform a photographic update of the collection of the Liege Mineralogy Lab, I found the specimens studied by Cesaro, Levy, Ungemach, Buttgenbach, Melon ... Surprises are great when sometimes the mineral is very small then the drawing in the textbooks is 5 or 10 cm wide.
Roger.

[Roger Warin]

Hi,
Still a short lesson for the beginner, with a specimen of the ULG museum.
A hexagonal dipyramid can have only a trigonal symmetry. This is the case of calcite. The crystal class has a threefold axis vertical. It is for this reason that the endings are often rhombohedra. The crystal is based on a rhombohedral lattice. There is no mirror plane perpendicular to the 3-fold axis (the 3-fold rotoinversion axis).
The calcite crystal photographed shows the main form (hexagonal dipyramid) terminated by the rhombohedral {10.1}.
In a non-twinned crystal, so there is no horizontal mirror plane.
But in the twinned crystal, it appears a typical upper symmetry of the twin. The composition plane is horizontal and it becomes a pseudo-plane of symmetry. The upper part is symmetrical versus the lower.
The cleavage planes will be reflected in the mirror. In addition, the upper rhombohedral termination also becomes symmetrical to the bottom one.
This is the case of this Rhisnes calcite (L {88.3} and {10.1}).

A note on the label, it says "hémitropie sur a1." This is an old French word to emphasize the twin on (00.1).
Definition of hemitropy: Special crystals consist of two halves joined together regularly, but reversed from their normal position, as if one had made a half turn on each other.
Roger.

[Roger Warin]

Hello,
Giuseppe Cesàro was a Belgian crystallographer of Italian origin (1849-1939). Reached in Liege 18 y. old, he was professor of crystallography at the University of Liège from 1891 to 1921. His scientific work was well known and he performed an important role during the birth of the “Union Minière du Haut Katanga” (Congo) (actually Umicore group) with his disciple Henri Buttgenbach.
He studied this remarkable galena from Freiberg (Saxony) and there he has discovered a new crystal form, the {551} trioctahedron.
Roger.

[Roger Warin]

Galena # 3296

An exotic trapezodron in galena from Freiberg (Saxony).
{001}, {111}, {744}.

Roger.

[Roger Warin]

Hi,
Galena pseudomorph of pyromorphite.
Kautenbach mine near Bernkastel, Rhineland-Palatinate, Germany.
Roger.

[Tobi]

I really enjoyed the last two German galenas from Freiberg (wonderful matrix specimen) and from Kautenbach Mine! The last one (called "Blaubleierz" in German, meaning "blue lead ore") is a really fine one. I actually don't like pseudomorphs (please don't hate me for saying this), but those hexagonally looking galenas are the only pseudomorph i would like to have in my collection :-)

[Roger Warin]

Me too, Tobi.
These pseudomorphs don't come from Freiberg.
Roger.

[Tobi]