Might try the Rocks forum here. Welcome.
A hardness test, some natural light views and a description of where you found it would be usefull if you post there. At this point it just looks like a well shaped river stone.
Definitely water smoothed or tumbled rocks are hard when you only have pics looks sort of like an opal but probably not other stones with the colors I'm seeing would be quartz or calcite... coming from a geology major that I don't use
That looks like a sock darning egg.(used for fixing holes in socks) I have one made of stone as well, hard to say what kind it is, looks like quartz or moonstone, but like I said, hard to say.... try the tests DDancer mentioned! Oh, and welcome to Tnet!