Is it meteorite or not?

[sonek23]

Hi I found that rock in river, in Poland. Under water it shines like a body of a fish. The shiny top was the part that we saw, the rest of the stone has round, rusty dots (+/- 1,5 cm) and was totally covered in mud and algae. What do you think it may be?
It is pretty big - about 20 cm in longest dimension and weights about 15 kg

It’s still pretty dirty

 

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[BoulderTroll]

A lot would depend on the local geology. I have seen very similar rocks in rivers below manganese deposits. Manganese ore tumbled in the river is quite shiny.
I'm sure there are better ideas out there though

 

[sonek23]

I was thinking about that too but as I’ve read there are no manganese deposits in our country

 

[Red-Coat]

Welcome to Tnet.

First question would be is it attracted to a magnet and, if so, how strong is the attraction?

Second question would be does it leave any kind of streak on the unglazed side of a porcelain tile? If so, how easily, and what colour is the streak?

Although I don't think it's a manganese nodule, it's not correct that they aren't found in Poland. They can be found on most ocean floors and consequently find their way into river systems everywhere, including from glacial flooding and oceans that no longer exist. Usually they're several million years old. Fe-Mn nodules are also reported from Albeluvisols in the Carpathian Foothills of Poland but formed in situ from alluvial deposits.