Granite was "Trilobite Trouble"
In Trilobite Trouble (in Morocco) at
http://lists.drizzle.com/pipermail/rockhounds_lists.drizzle.com/2013-April/001043.html
Pete wrote:
“I enjoyed reading that good story about the trilobite
industry, thanks for sending the link.
P.S., got a kick out of the 2nd sentence in the beginning
of the piece...
"...watch the sun go down over jumbled slabs of granite.
The desert here is reg, or loose stone, and its boulders
are packed tight with thousands of fossilized sea creatures."
I think that to many writers as well as "lay people",
any kind of hard pieces of rock has to be granite.”
You have a good point. My wife and I recently had
“granite” countertops installed. In the process, I noticed
that in terms of decorative stones, there is essentially,
with a number of exceptions, three types of stones:
“granite,” “marble,” and “slate.” “Marble” is any sort
of crystalline carbonate rock that will take a polish,
whether it be sedimentary or metamorphic. However,
some limestones are called “limestone.” In case of
“granite”, it is apparently applied to any holocrystalline
or porphyritic igneous decorative stone that takes a
polish. Slate is any fine-grained rock that can be split
into slabs that can used in roofing, decorative stone,
and various building applications
In the decorative stone business, these definitions
results various “granites” that are quite weird as far as
geologists are concerned. For example, the quite
beautiful and expensive “Azul Bahia Granite” from
eastern Brazil. It has a light grey groundmass with blue,
green, and black masses. It is not, geologically speaking,
a granite. Instead, it is a is a sodalite metasyenite that
is composed of sodalite (blue), feldspars and
feldspathoids (lighjt grey), mafic minerals (black), and
epidote (green). It was an odd feeling when our
contractor showed me a piece and told me it is a
“granite.”
The URL for “Azul Bahia Granite” :
http://www.newark.osu.edu/facultystaff/personal/jstjohn/Documents/Decorative-Stones/Metasyenite.htm
The website is at:
http://www.newark.osu.edu/facultystaff/personal/jstjohn/Documents/Cool-Rocks/Cool-Rocks.htm
http://www.newark.osu.edu/facultystaff/personal/jstjohn/Documents/Home-page.htm
Then there is the “Kozmus Black Granite” / “Kozmus
Granite.” Our contractor told me how difficult it was
to cut, install, and work with this stone. However,
despite these difficulties, he has through trial and error
figured out various ingenious ways of cutting, installing,
and otherwise working with this stone.
When he showed me a piece, I realized what the
problem is. It is that the “Kozmus Black Granite” is not
a granite as geologists use this term. Instead, this rock
is a mica schist with thin bands of extremely friable, very
weakly bound mica. I regard it remarkable that this
rock can quarried, cut into 2 and 3 cm thick slabs, and
transported. The amount of wastage during mining
must be quite high. I would personally, not have it on
countertop as it seems that it would be rather easy to
accidentally scratch or gouge it during normal use.
Regardless, a well foliated mica schist is certainly not
my idea of what I consider to be a granite as it is not
even an igneous rock. I am still trying to figure out
where in Brazil that it is quarried.
Some web pages are:
The Granite Gurus: Kozmus. Yes, it's a difficult stone.
http://www.granitegurus.com/2010/10/kozmus-yes-its-difficult-stone.html
Can anyone help me identify this granite?
http://ths.gardenweb.com/forums/load/kitchbath/msg0922381020804.html
Kozmus Black Granite
http://www.globalvlg.com/productsDisplay.php?id=180
As a person can see, there are a lot rocks that are
called granite, which geologically speaking are not
granite.
Yours,
Paul H.
