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What are they?

Coticule hones are natural earth stone quarried in the Ardennes region of Belgium from geological formations over 480 million years old.

Annual report of the Geological Survey of Arkansas Vol 3:

More detailed, however are the investigations into the nature of this stone by M. Renard.J These studies revealed the fact that the finer properties of the Belgian hone are due to the presence of microscopic garnets thickly and evenly distributed. Fine crystals of tourmaline and chrysoberyl are also present, and assist considerably in the process of abrasion. The stone is classed as a garnetyte by Renard.

It is the yellow portion of this stone which is valued as a hone ; and to preserve it from breaking it is customary to cement the pale yellow stone upon thin slabs of the purplish blue schist in which it occurs, unless the two are in contact and naturally united. This established custom of manufacturing the Belgian hone of two very characteristic stones furnishes excellent means of recognizing it. It is the best razor hone known, but it is not well adapted to other purposes.

The Non Metallic Minerals: Their Occurence and Uses:

According to Renard,1 the celebrated Belgian razor hone quarried at Lierreux, Sart, Salm-Chateau, Bihau, and Recht is a damourite slate containing innumerable garnets, more than 100,000 in a cubic millimeter. Like the Ratisbon hone, this occurs in the form of thin, yellowish bands, some 6 centimeters wide (2+ inches) in a blue-gray slate (phyllade). The bands are essentially parallel with one another and with the grain of the slate, into which they at times gradually merge. The chemical composition of a sample from Recht is given on the next page. The microscopic structure of the stone as described and figured by Renard is essentially the same as that of the Ratisbon stone in the collections of the U. S. National Museum, and the stones are practically identical in color and texture as well.

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