It looks like industrial waste. Did you check its properties? Something similar has been only seen at the scene of nuclear explosions where the sand and rocks fused. I forget the actual name for it but it was green.
It's light green, and had several deep veins of (what looks like) green "glass" inside it. What is it?
I found the rock on the beach about halfway between San Francisco and Santa Cruz, California. I can't imagine it could be `sea glass' since it's *inside* the rock (which is also green).
A few photos are in a (4MB) zip file at https://rcpt.yousendit.com/1105418315/cae4fbf68c0c0cd58551738f0527f9f5?cid=tr-cv-web-stnd-dl-literec-null-c-19073&s=19073
"side.jpg" has red arrows pointing to the two veins of green "glass"