Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/96

 84 the new planes produced on the first, while the planes which occur in the second, are more or less distant from it.

The difference which exists between what has been said by the Abbe Haüy in his “ Tableau Comparatf, &c.” with regard to the form of the primitive crystal of the laumonite, and that which I have myself established respecting it, will no doubt excite surprise. This difference for a long time detained me. The estimation, in which this celebrated mineralogist is so justly held, made me redouble my attention and care in the examination of this substance, but the several results of my inquiries have always afforded me the fullest confirmation of what I have said of the form of its primitive crystal, and of the measure which I have given of its angles. The circumstances that probably led the Abbé Haüy into an error, are the different varieties of crystals I have mentioned as forming the aggregations to which the fasciculated masses of the laumonite belong, but which, when this substance has undergone any alteration, are detached with much facility, producing so many isolated crystals, a great number of which present varieties differing one from the other. He would without doubt have obtained in this way a crystal analogous to that represented in fig. 14, as I have myself done, and which in reality presents a rectangular octahedron with its faces unequally inclined, and, regarding all the faces of this crystal as arising from a natural cleavage, he may have adopted it as being the primitive form of this substance. But two of the faces of this crystal are by no means primitive; they belong to the sixth modification. In no instance could the angles of this crystal be such as the Abbé Haüy has given them: the four faces which belong to the longitudinal ones of the primitive rhomboidal tetrahedral prism, meet each other two by two at an angle of 92° 30′; and the other four, of which two belong to the terminal faces of the primitive