BO ART, CARBONADO, AND GRAPHITE
T
HE black inclusions in some transparent diamonds consist of graphite. On crushing a clear diamond showing such spots and heating in oxygen to a temperature well below the point at which diamond begins to burn, Moissan found that the grey tint of the powder disappeared, no black spots being seen under the microscope. There also occur what may be considered intermediate foims between -the well-crystallised diamond and graphite. These are " boart " and " carbonado." Boart is an imperfectly crystallised diamond, having no clear portions, and therefore Xiseless for gems. Shot boart is frequently found in spherical globules, and may be of all colours. Ordinary boart is so hard that it is used
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