Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/255

 more readily obtained than the second, but it is extremely difficult to effect it parallel with the primitive planes. Yet having sacrificed very many crystals in the pursuit of this object, I possess several fragments in each direction, having brilliant surfaces. The hardness, and at the same time, the brittleness of the substance were obstacles to the discovery of its natural joints, which it was difficult to find the means of overcoming; but, after resorting to various expedients, I found the employment of a pair of steel pincers the most certain mode of effecting it. Being sharp, with edges about an inch long, they seize on the square prism, equally throughout its whole length; and, if the edges be carefully placed along the center of the prism, or parallel thereto, it splits, by considerable pressure, shewing planes parallel to two of the four sides of the prism. By the same means, it may again be split at right angles. In the endeavour to obtain cleavages in the directions of the diagonals of the prism, I found it impossible to lay hold of the sharp edges lengthwise, because the edges of the instrument were also sharp; and therefore took of the pyramid as nearly at right angles with the prism as possible, producing a plane, parallel to which it was requisite to procure another at the other end of the prism: applying then the pincers to these parallel planes, and in the direction of the diagonal, the prism sometimes yielded in that direction. But the crystals of tin are most readily split according to their natural joints, by placing them for some time in a common fire or a smith's forge; a slight blow with a hammer afterwards reduces them into numerous small pieces, and amongst such, I have found fragments in all the directions above mentioned; indeed this was the only means I could devise for obtaining them parallel with the faces of the primitive octohedron. The subjecting of the crystals to the action of heat, has however some disadvantages: not only are the fragments less brilliant