What makes square holes

[0lderthandirt]

Hello, I pulled a large rock out of the ground a few weeks ago and I'm now cleaning up some of the small rocks that broke off as it came up. This one caught my eye cause it's got a trilobite but after cleaning I noticed all of these rectangular holes on the side. The lines on the rule are 16th inch. Any suggestions on what would've created rectangular holes like this? 

Thanks for looking!

[Kane]

Very interesting! I wonder if they could be the impression of pyrite cubes. 

[grandpa]

I agree with Kane's general thought that this was some mineral with a cubic crystal structure that has since been dissolved away or otherwise removed.

[Tidgy's Dad]

Flourite, perhaps? 

[0lderthandirt]

It could be like pyrite although I've never seen any around here, there is quartz though. I just cleaned the ends and found 2 slots about the same width. They go about a half inch deep in the middle.

[Ludwigia]

There are a number of possibilities, since a good number of minerals belong to the cubic system. Maybe your best bet would be to find out more about the mineralogy of the location.

[0lderthandirt]

I think you guys are right, must be mineral. The only thing I could think of was an ancient relative of SpongeBob SquarePants.

Thanks for your collective wisdom!

[JamieLynn]

perhaps crinoid segements that have eroded out. It seems like there is some "banding" like crinoid stems would leave behind. 

[0lderthandirt]

2 minutes ago, JamieLynn said:

perhaps crinoid segements ...

That was exactly my first thought because I've got a lot of that nearby. The reason I ruled that out was the inside face is flat and the corners are sharp. The crinoid castings are more like half barrel on the inside. 

[oilshale]

Ordinary rock salt will form cubic crystals. If the salt is later dissolved out by water, cubic cavities could form.

[Pippa]

Quote

perhaps crinoid segments that have eroded out. It seems like there is some "banding" like crinoid stems would leave behind. 

As Jamie Lynn posted above.^

I have a couple of hash rocks with such squares and rectangles. They're always surrounded by other crinoid bits.

I have better examples than the one below, but haven't got photos handy. 

 

On the other hand, your rock isn't fossiliferous. Plus yours do look much more "mineral" than mine below. So there's that.

 

[0lderthandirt]

Here's a couple crinoid rectangle castings from my place, this is why this was my first thought but you can see the rounded interior. You're right the rock isn't loaded with fossils. My thumb is on a brachiopod that was cut in half when the rock broke and there is a small trilobite rear end near that. You can also see the cross sections of a few shells on the side with the squares but that's about it. The big rock that came off of weighs about a ton and unfortunately it's the same thing, only fossils are really just on the top.