Here's a post explaining a little more about the Manganese inclusions I mentioned above, in both Coticules and Belgian Blue Whetstone...
This kind of inclusion is generally regarded as quite desirable in Coticules, and it tends to take the form of either dark lines that look like cracks, or kinda blotchy leafy patterns called 'dendrites'. If you look at Tom's stone in the post above, those dark lines I imagine are Manganese, rather than cracks in the traditional sense. Here's a stone of mine with some dendrite type inclusions:
This one shows both lines and dendrites, you can see how they often occur together:
To be more precise this is Manganese Dioxide, also known as Pyrolusite, which is a black or dark blue coloured mineral with a slight metallic sheen, and it's softer than steel so it doesn't affect the sharpening ability. The reason it's regarded as desirable is because the formation of Pyrolusite happens along with that of Garnet, so stones with noticeable Manganese inclusions tend to have a high Garnet content and consequently be quite fast.
What's less commented on though is that the same Manganese inclusions can occur in BBW too, especially naturally bonded pieces from near the yellow coticule layer. You can see what it looks like in the blue-ish blobs here on the bottom of the stone and sides:
And in this picture of the same stone you can see one of these dark blue blobs extending from the BBW up into the coticule, where it becomes one of the leafy dendrite patterns in the first pic in this post:
---
So yeah - that's what Manganese inclusions are like in Coticules and BBW, and they’re worth looking out for.
This kind of inclusion is generally regarded as quite desirable in Coticules, and it tends to take the form of either dark lines that look like cracks, or kinda blotchy leafy patterns called 'dendrites'. If you look at Tom's stone in the post above, those dark lines I imagine are Manganese, rather than cracks in the traditional sense. Here's a stone of mine with some dendrite type inclusions:
This one shows both lines and dendrites, you can see how they often occur together:
To be more precise this is Manganese Dioxide, also known as Pyrolusite, which is a black or dark blue coloured mineral with a slight metallic sheen, and it's softer than steel so it doesn't affect the sharpening ability. The reason it's regarded as desirable is because the formation of Pyrolusite happens along with that of Garnet, so stones with noticeable Manganese inclusions tend to have a high Garnet content and consequently be quite fast.
What's less commented on though is that the same Manganese inclusions can occur in BBW too, especially naturally bonded pieces from near the yellow coticule layer. You can see what it looks like in the blue-ish blobs here on the bottom of the stone and sides:
And in this picture of the same stone you can see one of these dark blue blobs extending from the BBW up into the coticule, where it becomes one of the leafy dendrite patterns in the first pic in this post:
---
So yeah - that's what Manganese inclusions are like in Coticules and BBW, and they’re worth looking out for.
Last edited:
