What kind of rock is this?

Question

http://i66.photobucket.com/albums/h253/jthreattix/rock.jpg?t=1215638073

http://i66.photobucket.com/albums/h253/jthreattix/rock_1.jpg?t=1215638106

http://i66.photobucket.com/albums/h253/jthreattix/rock_2.jpg?t=1215638131

It's been in my house as far back as I can remember. (I'm 22) It's "clear," and weighs about 3 pounds, (1.3kg) and feel's fairly smooth. It's about 6-7 inches wide both ways (16-18cm), and 5-6 inches tall (13-16cm).

Answer 1

i have never seen a rock or stone like this..

i think you should talk to some geologist..it's very strange rock..

Answer 2

looks like glass, and not natural glass but manufactured glass.

Answer 3

Looks like glass.  The concoidal fracture pattern is similar to that of glass.  Natural glass is called obsidian.  I havn't seen clear varieties before, but there is no reason it can't happen in nature.

Another option is that you simply have a large chunk of glass that is not natural, but created by someone melting a bunch of sand.

Weight it accurattly then see how much water it displaces.  Weigh the water.  You can then figure out the density which can help you figure out what it is.