What is this?

[lithicacid326]

Hi all,

I found this at the bottom of an old cistern yesterday. Cistern dates from early 1800s to post-Civil War era. Could anyone help me out with figuring out what it is?

 

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[CCDAMEEK]

Could use some more photo's to help identify it. It appears to have been broken off a larger piece, based on the sharp points & uneven angles.
Possibly is part of an old cast iron stove. Many had an oval exhaust opening on the top-rear of the stove, which then would be adapted to a round stove pipe.
Something like this, but it would be sized by the overall size of the particular stove.