Many years ago, we would like to differentiate ores they have several common physical characteristics like colour by their shape. So, in 1669, Sténon tried to classify minerals from more rational criteria. He noted the crystals of a same product, but with different shapes due to the different speed of face development, some of angles are constant. but, Sténon did not develop more his observations.
In 1783, from the study of synthetic crystals, Romé de l'Isle expressed the law of the angle constancy as: "The inclination between faces is a constant and invariable within each kind."
Also, at the same time, he though "the various crystalline shapes for a same mineral are only deviations easy to deduce from a one shape called fundamental. "
But, At this time, there was always a deep variance between mineralogists about the number and the kinds of these fundamental shapes. Thus, Buffon , The most famous scientific of this century said that: " the crystallisation shape is not an invariable characteristic but more ambiguous and more fluctuating than all the characteristics allowing to distinguish minerals."
This was in 1784 thatthe priest Haüy , from experience of cleavages, established the crystallography. The books edited by this scientist were in 1784: the "l'Essai d'une théorie sur la structure des cristaux" (Essay of a theory on the minerals structure), in 1822, le "Traité de cristallographie" (Treatise on Crystallography), and the same year, le "traité de Minéralogie" (Treatise on mineralogy).
The priest HAUY noted the constancy of shapes of individual issue of a same vegetal kind. Then, he asked himself this philosophical question:" why Life, so independent from the outside conditions, is it producing fixed shapes, even though minerals, whose composition is never changing, has so variable shapes?"
iside his " Essai d'une théorie de la structure des cristaux " (Essay of a theory on the minerals structure), Haüy answered to this question as (translation is following): " L'aspect seul de ces polyèdres (les cristaux), sur lesquels il semble qu'une main exacte ait porté la règle et le compas, pour en fixer les dimensions, indique un objet susceptible d'être soumis aux méthodes rigoureuses des sciences mathématiques : Mais il fallait trouver dans l'objet même des données suffisantes pour exclure toute supposition arbitraire, et pour conduire à des solutions qui représentassent les vrais résultats du travail de la Nature. "the aspect of these polyhedra (the crystals), on which it seems an exact hand put on ruler and compasses, to fix their dimensions, point an object that can be submitted at the rigorous methods of mathematical sciences: But it should be necessary to find within this object itself enough data to eliminate arbitrary supposition, and to lead to solutions representing the true results of the nature working."
"Une observation que je fis sur le spath calcaire en prisme à six pans, terminé par deux faces hexagones, me suggéra l'idée fondamentale de toute la théorie dont il s'agit. J'avais remarqué qu'un crystal de cette variété, qui s'était détaché par hasard d'un groupe, se trouvait cassé obliquement, de manière que la fracture présentait une coupe nette, et qui avait ce brillant auquel on reconnaît le poli de la Nature. J'essayai si je ne pourrais point faire, dans ce même prisme des coupes dirigées selon d'autres sens ; et, après différentes tentatives, je parvins à obtenir de chaque côté du prisme trois sections obliques :et, par de nouvelles coupes parallèles aux premières, je détachai un rhomboïde parfaitement semblable au spath d'Islande, et qui occupait le milieu du prisme. Frappé de cette observation, je pris d'autres spaths calcaires, tel que celui qui forme un rhomboïde très obtus, celui dont la surface est formée de douze plans pentagones ; et j'y trouvai le même noyau rhomboïdal que m'avait offert le prisme dont j'ai parlé plus haut.
"An observation I did on a six sides calcareous spath prism, terminated by two hexagonal faces, lead me to think the fundamental idea of all the theory it was. I noted a crystal of this kind, separated from a group by coincidence, had been obliquely broken in such a way that the fracture showed a clear cut, and with this lightening which we are recognising the Nature polish. I tried in this prism to obtain other cut following others directions; and, after several trying, I could obtain on each side of the prism, three diagonal sections: and, by new cuts parallel to the first ones, I separated a rhomboid absolutely similar to the Iceland spath, and which was located the centre of the prism. Surprised by this observation, I took other calcareous spath, as this forming a very obtuse rhomboid, this with the surface formed by twelve pentagonal sides; and I found inside the same rhomboidal core than the prism I presented before gave.
Des épreuves semblables, faites sur des crystaux de plusieurs autres genres, assez tendres pour être divisés nettement me donnèrent des noyaux qui avaient d'autres formes, mais dont chacune était invariable dans le même genre de crystal. Je crus alors être fondé, d'après les tentatives faites sur des crystaux mentionnés, et, d'après des raisons d'analogie, pour les crystaux que leur dureté ne permettait pas de diviser, à établir ce principe général, que toute variété d'un même crystal renfermait comme noyau, un crystal qui avait la forme primitive et originaire de son genre. "
Similar tests made on others mineral kinds, enough soft to be distinctly divided gave cores with others shapes, but which was invariable in a one crystal kind. Then, I though to be justified, from the tests made on the mentioned crystals, and, from analogy reasons, for the too hard crystals impossible to divide, to establish that all the varieties of a same crystal kind was locating, a crystal which had the primitive and founding of its kind shape."
So, the crystallography has been founded; so, it was possible to affirm minerals are presenting a constant organisation and they are not produced by an unorganised agglomeration of class, the geometrical architecture of the mineral individual is not less characteristic and harmonious than for a living individual. in the crystal building, regularly in a same mineral kind, elementary particles are closing themselves every time, and the crystalline shape is a characteristics of the mineral with so rigour as the anatomic body is characteristics of a animal or a vegetable. The shape, in all the cases, gives the sign of the individual and allows its diagnosis.
This comparison and the relations between the different kingdoms had been developed within the admirable book of Dastre " La Vie et la Mort "(The Life and The Death), which is clearly showing the majority of the nature laws considering morphogenesis...
... The Haûy works have so created the crystallography. This scientist admitted 6 kinds of primitive shapes, but today 7 are admitting. These are the crystalline systems. This same scientist has formulated the fundamental laws of the crystallography.
For conclusion, we say Mineralogy is, with physic, one of the science the most studied. It gives all the data indispensable on the structure and the properties of the solid products. It leads to large horizons on the material constitution. It is one of the bases of the chemistry and the chemical industry. It allows well understanding the economical problems appearing today so considerable and important...
Studying the nature only on its mineral aspect, it shows the simplest shapes of materials gets a notable organisation... The well-known organisation of the crystalline surroundings allows attaining general laws with high scientific importance they are also philosophical, making part of the general culture of a scientist.
M. PICON
" Eléments de Minéralogie "
Cours professé à la faculté de pharmacie de Paris
Lesson at the pharmacy faculty of Paris on 30's years |
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