Rock I Found Yesterday. I Don't Know What It Is.

[Ezra]

[Geologyhound]

Can you describe the texture of the rock or say where you found it?  If you look closely, does it appear to have tiny fossils or crystal surfaces that glisten in the sun?  Based solely on the color of the rock and the general fine-grained texture, I would guess at some extrusive igneous rock like rhyolite, or a sedimentary rock like limestone or shale.  There are a lot of differences in those rocks. Where you found it and what it looks like up close could help narrow that field (or suggest other possibilities).

[Ezra]

It glistens very much in the sun and it came from around a 100lb rock. The texture is smooth until it reaches grooves where it becomes rough and then smooth again. The pictures are not on a sunny day though.

[Gold Seeker]

When he asked where you found it, he was asking the general location of where you found it, next to a big rock doesn't give anyone any info to help ID your rock, the general location will help because someone can check what types of rocks are in that location which will help narrow down the possibilities of what it could be.

[Ezra]

Louisiana or baton rouge area.

[Geologyhound]

Down in that neck of the woods, it would almost certainly have to be a sedimentary rock. You have a lot of sandstones, mudstone etc.  Depending on where you found it, there is also the possibility it could be a chunk of limestone washed down river.  Since it glistens in the sun, at this point I would guess at sandstone or possibly limestone.  If you rub it or scratch at it with a screwdriver, does it shed any grains of sand?  Alternatively if you happen to have some dilute hydrochloric acid (0.1 molar), you could drip some on the stone and if it fizzes, it is limestone.

[Ezra]

Grains of sand didn't shed from it when i used a screwdriver or my finger. I have no clue what it could be. I found it stuck in the ground outside in the Baton Rouge area.

[Geologyhound]

You could try an acid test.  Typically, dilute hydrochloric acid would be used to check for calcium carbonate minerals and will result in vigorous fizzing.  Lemon juice or vinegar are weaker and will produce bubbles if watched for a period of time.  Muriatic acid is a commercially available form of more concentrated hydrochloric acid (with other impurities).  If you try muriatic, you may want to dilute some first.  Depending on your concentration, a 5 part water to 1 part acid dilution may work.  When diluting acid, always add the acid to the water - not the other way around.

Drip your acid on the rock and watch for a reaction. With weaker acids, you may want to immerse part of the rock in the acid and see if bubbles form.

[Ezra]

Nothing happened. To tell ya the truth, I have no clue what it could be cause I poured  a lot of vinegar on a part of it and nothing. I don't think it is sand stone either.

[Geologyhound]

The problem with pouring a weak acid on limestone is that the acid runs off and it is difficult to tell whether bubbles formed or you just trapped air bubbles in nooks and crannies of the rock when you poured the fluid over it.  Ideally, with a weak acid, you would immerse part of the rock and watch for a few minutes. If bubbles appear where there were no bubbles before, that is a positive result.  With a stronger acid, most limestone would just fizz like crazy and there is no mistaking it.

Depending on the limestone composition (carbonate versus dolomite versus aragonite), it may not react with acid without some help. For example, dolomite won’t react with acid unless you powder a sample of it first.

If you open your mouth and breathe on it (make sure it is dry first ) like you’re trying to fog up glasses, do you get a musty/earthy smell?  If so, it could be argillite – a slightly metamorphosed mudstone.  That wouldn’t quite fit with the glistening description, and most argillite should be relatively soft. But it’s a thought.

Any chance it could be a chunk of Portland cement?

Let me know if any of those work out.  Beyond that there’s not a whole lot I can do without seeing it in person. However a geology department at a local University, or even a local rock shop, might be able to ID it once they see it in person.