Porphyry

[abknight@zzzzzz]

Pardon me.  I thought I might republish under a proper
heading in case George isn't interested in reading further
about hammerbeams.
I am completely gone over porphyry here in Missouri.  It
occures here in boulders exactly in this color of royal
purple.
http://en.wikipedia.org/wiki/Porphyry_(geology)
It varies greatly over short distances.  There are many
types near me.  Close by my favorite is a greenish black
when split or polished, or bright verdigris when honed.
It is a complicated mix of green and black chunks of
material millimeters to centimeters across.  Hammered with
a nine point chisel it glows bright light green amid the
white chisel crush.  My nearest and favorite is a mixture
of chunks of purple and olive green when split or
polished, honed it is a magic field of bright turquoise
and violet.  This is a stone that begs to be simply shaped
and honed.  It is very friable.  It four or nine point
chisels very well and wastes away quickly due to its
brittleness.

In the rough it looks something like the ryolite porphyry
on this page.
http://www.drexel.edu/coe/enggeo/rocks.html

Here is a poor shot of a Stephen Cox work in porphyry I
think.  It looks as though he was happy with the glowing
hammered look
http://www.meadowgallery.co.uk/gal-2004-03/slides/Dsc_04.html
I the freshly bumped and crushed state the colors, pinks
and greens and blue-greens are pastel, candy-like.

Ah, I've been stalling.  Here is a good photo of the
Egyptian porphyry, similar, dissimilar from ours, in a
Stephen Cox work.
http://www.tate.org.uk/servlet/ViewWork?cgroupid=999999961&workid=20580&searchid=8430&tabview=image

Thanks to Tomas Lipps who told me of Cox and informed me
of the royal heritage of Porphyry.  I think Stonenexus may
have dealt with the African quarry.