Is this pure Beryllium or what. How can I tell. Weighs 4-3/4 lbs. or is it just a paperweight.

Put in furnace, turn it up to 2400 deg. F. If it melts before it gets up to heat, it isn't beryllium.

what is pure Beryllium worth ?

It is a beryllium-copper alloy.  It is non-magnetic, and does not spark. Its dust is carcinogenic

We know Berylco for their tools, but, the tools are a small part of their business, they are a major maker of special alloys.
You have a raw ingot of some alloy....possibly BeCu...perhaps something else...

http://en.wikipedia.org/wiki/File:Beryllium_Copper_Adjustable_Wrench.jpg

Here is a finished product.