Re: Franklinite found somewhere other than Franklin?
- From: "=?x-user-defined?q?=AB?= Paul =?x-user-defined?q?=BB?=" <" =?x-user-defined?q?=AB?= Paul =?x-user-defined?q?=BB?="@houston.rr.com>
- Date: Thu, 07 Sep 2006 03:23:27 GMT
Dan wrote:
Hey,
I live about 30 miles north of Franklin, . From what I've been told,
glaciers went through this area, carving big gashes in the hills. My
backyard is basically a "gulley", where rain washes down from both
hillsides. This exposes a very wide area of rock.
For several years I've gone in the backyard to get material for rock
walls. From what I've been told, the area is primarily gneiss and
other types of granite, with some slate here and there. I never took
an interest in the types of rocks back there, it was all just building
material.
About a year ago I found some rocks which seemed interesting. On the
surface (and to the naked eye) they looked different from the regular
gneiss, like cinder-block rejects....lumps of greyish-white mixes
(more grey than white). I broke one open, took a photo and asked a
friend who's an amateur geologist what he thought. He said it looked
like ancient seabed material. He theorized the red streaks and spots
were types of tiny garnets. He stopped there, and the matter was
closed and I lost interest again.
My nephew just recently visited and we went to the Franklin mineral
museum. I was a bit shocked to recognize that the rocks I was picking
up from the backyard looked extremely similar to the mixed types of
franklinite (when mixed with other minerals).
I purchsed a black-light and checked out the rocks from my backyard.
On the weatherd surface, they are boring...only a tiny fleck of
fluorescent orange here and there, barely enough to be noticeable.
They are also a deep purple, but I guess that was simply the
black-light being too close to the rock. However, when broken open it
fluroesces a very deep purple with hundreds of small flecks of a rich
yellow-orange (not reddish orange like calcite).
From what I've read, the purple (which in regular light is white)
could be hardystonite, and the orange could be clinohydrite, a mineral
closely related to hardystonite in chemical composition. I cannot pin
down the "visible-light" color of the fluorescent-orange areas in
regular light. I attempted an "acid test", pouring vinegar on the
orange areas to see if it would dissolve like calcite, but the orange
stayed in place, even after several days.
The rest of the rocks are a mix of black and white, with shiny
cleavage and a magnetite-like look to it. Even after eons of
weathering I've found a few of them when the cleavage reflects in the
sunlight. The rocks are very slightly magnetic, and they are easily
fractured. They are not common in my backyard, but with enough
searching they are not difficult to find. Some are twice as big as a
basketball, and are relatively dense.
I am not an expert, just an amateur who's obtained an interest in the
local geology. I'm theorizing that a glacier might've plowed through
the Frankiln area and dumped all these minerals along it's route. Is
this a valid hypothesis? It seems significant that large amounts of
Franklinite (and related fluorescent minerals) might be found outside
the Franklin area.
Thanks for any thoughts,
Dan
Try here:
http://www.uvminerals.org/
That is a great museum for the local rocks. I really liked the 3-D model of the
mineral deposits and mined volume. The minerals were laid down similar to black
smokers and then contorted into a near vertical mass during one or more of the
Appalachian orogeny events.
http://geology.about.com/library/bl/maps/blnewjerseymap.htm
.
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