Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/67

 a rough fracture; these are generally called Diamonds of nature. The fracture of this gem is the criterion sometimes relied on by the overseers of the mines in Brazil. Whena stone is delivered to them of a rude appearance, both ill formed and of a bad color, they have recourse to the hammer, especially if it exceed in size the Diamonds usually met with; they hold it upon a hard substance, and give it a sharp blow, should the fracture prove distinctly lamellar they are convinced that it is a true Diamond. In the treasury at Rio de Janeiro, I noticed three or four flat pieces of a bad brown color, an inch long by half an inch in breadth, and about one eighth in thickness.—To this rough kind of experiment may be attributed the fragments occasionally met with.

may be distinguished by the senses of hearing and feeling, in the following manner. If two diamonds be held between the fingerand thumb, and rubbed strongly together, a peculiar grating noise will be pro-