Help me identify the “brain rock”

[BanjoEllen]

Hello! This rock has been in my family for as long as I can remember. We always called it the “brain rock” when we were kids. It was my grandma’s and she always said it was a geode. That would be awesome but I have my doubts. I would just break it open but if it’s not a geode then I’d rather keep it intact and use it in the garden! I don’t know where it came from. We are from the mountains of western North Carolina but I know she did some traveling in the midwest and southwest, or it could be from truly anywhere.
I’ve tried to include some photos that I hope are helpful. It weighs 22.4 lbs. and is about 10 inches in diameter.

 

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[apdp]

Most likely geode. Find your local rockhounding club and have someone take a look at it. From there find someone to cut it for you. Breaking it would be a shame as it is your family's old keepsake.

 

[Al D]

Hello! This rock has been in my family for as long as I can remember. We always called it the “brain rock” when we were kids. It was my grandma’s and she always said it was a geode. That would be awesome but I have my doubts. I would just break it open but if it’s not a geode then I’d rather keep it intact and use it in the garden! I don’t know where it came from. We are from the mountains of western North Carolina but I know she did some traveling in the midwest and southwest, or it could be from truly anywhere.
I’ve tried to include some photos that I hope are helpful. It weighs 22.4 lbs. and is about 10 inches in diameter.

Here is an idea, have a hole drilled in it, then you could use one of those harbor freight borescopes to look inside it, you would see the geode crystals, if they exist, and still keep the rock intact.

 

[hvacker]

A geode usually fells light for it's size. That's because it's hollow.
If you test it for calcite it might have been a cave rock. A little vinegar should fizzle.
Or if you don't mind handling it, HCL (hydrochloric)acid. I resembles calcite I've seen in some caves.

 

[Indian Steve]

It looks a lot like geodes that I found 50 years ago in my grandparents creek in southern Indiana. I still have a 5 gallon bucket of smaller ones.

 

[IAMZIM]

What hvacker said.

 

[giuhalftrack]

it looks like a concretion mineral to me.. you can do this test:

give some drops of diluted 5% HCL just to discover if the material is a carbonate, if you see effervescence it's a carbonate....
you can try first the test on concrete just to understand what i'm talking about.

maybe a mineral substitution of a fossil.. i cannot recognize what kind.

p.s. i'm a geologist