Blue Belgian Brocken, As A Gouge Stone

Honing stones are aids for the manual honing of ground tools. A distinction is made between natural stones and artificial stones. Natural stones come from quarries and are partially different in size, quality and appearance. 
 

Blue Belgian Brocken - a water honing stone.
In the search for an alternative to the increasingly dwindling yellow stone, one came across a high-quality sharpening stone with almost identical properties, only in a blue-grey colour, which comes from iron oxide. This stone contains approx. 30% garnets compared to the yellow stone with approx. 40%. As a result, this blue stone is a little “slower” than the yellow but also more durable.