I thought it was Kimberlite, but it is Peridotite according to the linked page.

> > > > More trivia:
> > > > Where is the southern-most point in the United States? I went there once a long time ago, but when I went more recently, it was thousands of miles away. How can that be?
> > > > Howard
> > >
> > > That would be some point in Hawaii, I believe. I'm not looking at a map so I don't have a name for you.
> > >
> > > Fer"If only this Internet were useful for finding that out"rick
> >
> > The green sand beach on the big island of Hawaii is the southern most point in the United States. I assume you flew over it last time, Howard.
>
> I'm going to have to brush up on my tricky question technique. The point is that before 1959, when Hawaii became a state, Key West, Florida was the southernmost point in the US. After that, it became South Point -- I won't attempt the Hawaiian name -- which is the location of the famous green sand beach.
>
> But I cheated a little. The first time I went to Key West was 1969, some 14 years after it lost that distinction. However, the big, ugly, red and black marker was still there at the time and remains there today.
>
> Next question: What makes green sand green?
> Howard