odd stone or fossil?

[hndmarshall]

2 inches long and one inch wide

the outside seems hard and thin ... the inside is a totally different material very fine hard to see any grains at all even under magnification check photos (silt?) not sure.

found in gravel load from Brazos River west of Houston.

the outside is? 

I am thinking concretion? .... some one told me possibly egg but I don't think so I don't get that feeling, outer coating seems wrong to me not like what I would think a shell would look.

has any one see a concretion like this before?

 

[ynot]

Looks like a tumbled sandstone with a mineral incrustation called "desert varnish".

[hndmarshall]

21 minutes ago, ynot said:

Looks like a tumbled sandstone with a mineral incrustation called "desert varnish".

desert varnish.....sounds interesting

[ynot]

20 minutes ago, hndmarshall said:

desert varnish.....sounds interesting

 

After exposure the iron and other metals in the rock will oxidize at the surface . In a desert environment there is not enough water to leach the minerals out and carry them off, so they build up creating a dark surface coating.