Petrified ash cakes?

[RandyBoBandy]

So I was sifting through the ash in my stove the other day looking for some hidden coals to help relight with and I came across this. A large fused together cake of ash. It is rather hard and odd. Made thing of lava rock. Anyone have any suggestions as to how and why?

 

[kennyp2339]

That's a clinker, sometimes wood has absorbed minerals and once burned they fuse together, I get those from time to time.

 

[brickie]

I can't resist!

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[jetsam]

They break up okay and don't seem to bother the plants. I leave them in with my ash before I scatter it or compost it.

 

[Woody5506]

I get them too after not cleaning out for a while. Didn't really think much of it quite honestly.

 

[peakbagger]

Clinkers are mostly inert minerals in the wood that have reached high enough temperature that they have partially fused. They are a minor annoyance for woodstove owners but a potentially a big PITA in a power boiler. The clinker can form on the steam generating surfaces forming insulation between the hot gases and the tubes. On trash burners the clinker will adhere to the tubes so tightly that explosive are used to remove it.