Hi, could someone please help me identify a mineral? I do not have a very good picture, sorry about that. It is a sort of grey/blue, which gets darker at the very center, but stays the same color at all other parts, which can be sharp at some of the more acute angles. I find it in a creek, and think it is some kind of compressed sandstone or such-like, because when I find the mineral non-broken, there is always a layer of sand between the rock and the interior mineral. Thank you in advance for any answers.
I think you have a piece of chert, which often has a sort of rind on it (your 'layer of sand').
Chert may occur in equant lumps, in lumpy layers, or anywhere inbetween. It looks like yours are at least flattish in shape. The interior of chert lumps ranges in colour, including blue-greys. The extremities of the lumps can be smooth or fairly pointed; fractured surfaces can give very sharp edges.
Chert often forms in limestone rocks such as chalk, but also occurs in other rock types.
Here's a somewhat layerish piece of chert with a rind -
Have a read of that page, and you'll see a description of pastelite chert, whose colours can include blue.
I do't suppose your creek is Burro Creek, Arizona is it?
That is a known locality for pastelite - eg. see: