Mention of this rock came up during discussion about the
Spherulitic Rhyolite post in the "Artifact" section. And,
thanks to John Frazier, a specimen appeared for our perusal.
One question these two materials bring to mind is the use
of the words "orbicular" and "spherulitic" when describing rocks
with spherical formations. The question being; Are there times
when one term or the other is more appropriate and is there
any difference, implied or definitive, between "orbs" and "spheres"?

Comparisons will have to wait. First we have to give a
proper introduction to such a famous member of the NC Rock family.
One of the first descriptions of NCs' Orbicular Diorite comes
in a 1904 report by T.L. Watson who visited the outcrop
in the summer of 1903.
"Exposures of the orbicular rock occur in the eastern part
of Davie County on the Hairston Farm, about 10 miles west
of Lexington and within one and a half miles of the Yadkin River."
and,
"Further interest attaches to this rock for the reason that,
as yet, it forms the only example of orbicular structure
among deep-seated rocks found in the southern Appalachain
region, and also it adds a rock type which. in some respects
is a new one developing nodular spheroidal structure."

By this, I believe, he is talking about the many different
minerals present in this rock and the unique "singular" way
in which they formed. Although all a part of the same rock
each mineral seemed to find its' own individualized pocket
to grow in, making microscopic identification much easier
and interesting.
Please note the two different tones of green in the spheres
themselves.

Due to the schiller effect of the fibrous green spheroids the
Dino-Lite is about useless in trying to get a close-up of
them, but here is one attempt and then a few close-ups of
the Titanite crystals.

Glad you like the report, John.
I wanted to give this rock some of the respect it deserves,
besides for the fact that it came from your collection,
Thank You Very Much.
There's alot going on in this rock so it is a great one to study.
The remarkable delineation of each integral mineral begs you
to take a closer look.
Unfortunately, I have found no reports of anyone having
done so since the time of the Thomas Leonard Watson
report, 1904, referenced above.
This also makes for interesting research, as I alluded to above,
in that the mineral or geologic terminology and names of
some minerals or mineral forms have changed/"grown" some
in the last 100 years.
No wonder you got to keep on learning stuff, they keep
changing the names of stuff on us!
The "Diallage" and "Uralite" are good ones to start with.
For instance, the definition for Diallage in the Websters
Dictionary of 1828 is;
Diallage, n, (Gr. difference, alluding to the difference of
luster between its natural joints.)
A mineral, the Smaragdite of Saussure, of a lamellar or
foliated structure. It's subspecies are green-diallage,
metalloidal diallage, and bronzite. The metalloidal subspecies
is called schillersteing or shiller spar."

And then by 1913,
"A dark green or bronze-colored laminated variety of
pyroxene, common in certain igneous rocks."

As time goes, so do the rocks.

It appears we were misinformed about the Monazite. I have
not found any list of minerals for the Orbicular Diorite that
contains Monazite. (Not even a mention, which I find a bit
peculiar.) But they all list Titanite prominently, so that's why
I'm guessing that's what this is. Real pretty brown little crystals. I will bring some to the next club meeting and try
the gieger counter on them.

I need better magnification, and we'll see if polishing helps,
or hurts, but I still want to take a closer look.
Another quote from Mr. Watson;
"Abundant prisims of Apatite, usually of fairly large size,
are included in the feldspar. Some of these are in cross-
sections that show the perfect hexagonal shape, others
are longitudnal."

Anyone having fun yet!
Joe

Oops, You are quite right, John.
It was a gross over-assumption for me to jump to the
conclusion that those small brown crystals were Titanite
based on the Watson report. I have re-read the report and
now realize that his description of the Titanite was the only
one that would fit and so I assumed.........wrongly.
Re-reading the description of the Titanite leaves me to
believe I have yet to identify it in the specimen.
But, it is hard for me to believe that there is no mention
of these crystals in Watsons' report they are so obvious.

I have the 1978 reprint of "Mineral Collecting Sites in NC",
Wilson & McKenzie, and it states; "Some of the orbicules
contain monazite crystals up to 1/4" by 1/4"."

I will definitely be checking them for radioactivity.
Joe

So what are you trying to tell me, Dennis?
That it's going to cost me a slab of Orbicular Diorite to get
my hands on the Geiger Counters?
We might be able to work something out.
I'm going to send you a PM to talk about your schedule.

Last time I saw those spheres was during the Out of the Vault
exhibit at the Natural Science Museum. Love them and the
collection of large blocks of different woods stored with them.
Have a good walk or two!
Joe

Very interesting Joe. Thanks. And very beautiful material too.