Before explaining, or rather attempting to explain, the phenomena of some of the prominent physical properties of the mineral, it is proper that we should give a description of its forms and its natural appearance as it is taken from the mines, so that our reader may become more familiar with the subject. We will not, however, venture very far among the dry details of crystallography, even if it be a subject of great interest to the student in science. The stone which so readily attracts the eye by its dazzling splendors after it has received a definite form and polish from art, is seldom attractive to the view unless it occurs in a rare and perfect form of crystallization. Even then, in this primitive state it exhibits none of the rainbow play of color which makes the stone so celebrated and so beautiful. In reality, in these rare conditions it is seldom if ever so lustrous and pleasing to the sight as crystals of many other minerals. In general, the diamond is so obscure in its attractions that practised eyes are required for its search. Recently the distinguished savant Von Tschudi, in visiting some of the diamond mines of Brazil, was unable to distinguish readily the gems as they lay in the washed cascalho, while the trained eyes of the negro miners picked them out with ease. It has been stated that the diamonds are always or nearly always covered with an earthy crust of various hues, especially greenish or yellowish, which is hardly the fact; for what appears to be a crust is often caused by the salient edges of the laminæ, among which a little earthy or coloring matter has been introduced. These extraneous colors generally disappear when the surface of the stone is removed; and, in fact, the degree of their intensity is very much modified when the rough gem is placed in alcohol or in any fluid of high refraction. The dull, whitish appearance seen in the natural diamonds is also produced by the action of fire, which raises the edges of the laminæ, producing a faint milky aspect. The primitive form of the mineral is the octahedron, and many irregular masses may be reduced by cleavage to that of a double pyramid. These octahedral crystals are sometimes as perfect in outline as a mathematical model, with clean-cut angles and smooth faces. In some specimens the edges may be truncated, that is, as if they had been flattened or ground off by mechanical means. Generally, however, the crystals are of the form of the octahedrons with rounded faces. The dodecahedrons, with their twelve faces, and the cubes, with their four sides, may also be reduced by cleavage to the primitive form of the double pyramid. Sometimes two crystals are united, forming what are called hemitrope or twin crystals. Then, again, a number may be grouped together, assuming on the whole a globular-like mass. But they are decidedly different from the globular, which in their form of crystallization radiate from the centre of the crystal.