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Mineral
of the Month--February
2008
Exotic Pegmatites, Part 1
Various and Sundry Minerals & Chemistries
At least SiO2
"Exotic
Pegmatites"
By Ken Casey
Preface
Hello, again,
fellow adventurers! This month, our
Mineral-of-the-Month
takes us all over the
First State to find quartz in all it's forms. In this two-part
series on Delaware Quartz, we'll
venture across all three counties: New Castle, Kent, and Sussex in
search of our most popular
silicon mineral.
Summer is still lingering, but bring your light jacket. The weather promises to be
bright and
sunny today, so
Let's go!
Introduction
In part 1, we covered igneous quartz and bedrock,
and touched upon our beach sands. This
month, we will study the sands and pebbles of time that lie around
Delaware’s coast, rivers,
creeks, and aquifers. In other words, sedimentary quartz.
Erosion by wind and water has deposited
grains of quartz sand from microscopic to larger
pebbles here. Though glaciations did not officially touch Delaware
topography, subsequent
erosion of glacial material left to the north of us, from Pennsylvania
and New Jersey, did arrive
here eons ago.
Work by geologists gives us an overview as
to the surficial occurrences of tumbled quartzes.
And, digs by both archaeologists and gravel miners point to areas rich
in rounded silicon dioxide,
which can help us to paint a picture of the widespread availability of
this mineral to view and to
collect.
As quartz was geologically created in a
range of colors, whose original occurrences span the
greater northeastern United States and Canada, the area of colorful
material which have aggregated
over Delaware’s ancient landmass is vast. So, that means that we can
find colors ranging from clear,
white, yellow, pink, purple, and green strewn across our local
landscape.
Though most terrigenous erosional detritus
is from places outside of Delaware, these mineral
morsels do belong here by virtue of having arrived under our feet
thousands of years before native
Delawareans came here. Since they are ours to collect (with appropriate
permissions, of course),
we can assemble a vast array of colorful specimens to show and to share!
So come on along, we have another Delaware
Quartz fieldtrip to make!
We can, however, take our pick of geology
hikes to view them in situ. Or, as the Delaware
Geological Survey has organized itineraries for us, called
GeoAdventures.
We''ll share
a bit
from the Survey's suggestions, coupled with our club's and this author's field
experience.
Our article will landscapes.
Enjoy!
Why Delaware
Quartz?
Our local . Please do join us!
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And,
with a simple trail off of the entrance to the parks, such
as to our
Brandywine Creek State Park, north of Wilmington,
we can quickly find specimens to observe.
So,
grab your walking sticks, and let's hike!
Easy to find garnet in host
rock, BCSP
(Photo by Ken Casey) |
What's in a name?
Q uartz
(Source:
http://en.wikipedia.org/wiki/Quartz)
Much of
Greek
(Source:
http://www.jewelrysupplier.com/2_garnet/garnet_mythology.htm)
The name “quartz” was grandfather prior to
1959 by the IMA.
Delaware's quartz
is a
silicate of chemical formula
SiO2.
It
On the
Moh’s Hardness Scale,
it ranges from 6.5-7.5.
Where found?
DELAWARE. Pegmatites?
DIXON'S QUARRY.—Columbite.
NEWARK.—Quartz crystals, doubly terminated, loose in soil.
http://books.google.com/books?id=KAgRAAAAIAAJ&pg=PA504&lpg=PA504&dq=delaware
+and+quartz&source=web&ots=A2bqv9a2Qd&sig=_wEeLUzK-xny2snS2tC0vN5QRRY
Though
(Source:
http://www.uwgb.edu/dutchs/EarthSC102Notes/102ROCKS.HTM)
In the photos below,
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of Appalachian mountains and plateaus overlooking Susquehanna
River at Red Hill, Hyner, PA (Photos by Ken Casey) |
Delaware has
(Source:)
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What .
(Source: )
Garnet-laden drill core samples
(Photo courtesy of Oliver Holm,
Geoscience Australia) |
For example,
Our Piedmont
Therefore,
Gneiss is the primary
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| Almandite Garnet crystal
Photomicrograph, South Carolina's Appalachian Piedmont |
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Almandite Garnets the size of dimes in
matrix,
Brandywine Creek State Park |
| Photomicrograph by
Harmon Maher ; Photo by Ken
Casey |
The smallest
Delaware
Geological Survey.
The largest may be perus
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Our eastern Piedmont
runs northeast-southwest, the entire length of the middle-Atlantic
coastal area, intersecting at nine states and the District of Columbia.
So, of course, similar garnet occurrences can be found in other states.
Our region is marked with outcrops, exposing a modest wealth of garnet
viewing areas. We will concentrate on our area’s
Wissahickon Formation
and
Wilmington Complex
of rocks.
Generalized Piedmont Map; Piedmont is Tan
(Courtesy of Karl Musser, Cartographer, wikipedia.org
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More sp
(Source:
http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_delaware.html)
A rare igneous garnet is
found in the pegmatite of the
Woodlawn Quarry. The locale may be
found
in the red area of the
Generalized Geologic Map of Delaware, below.
Why not try this one:
Woodlawn
Quarry: A GeoAdventure in the Delaware Piedmont
Generalized Geologic Map of Delaware, courtesy of the Delaware
Geological Survey
Prepared by: Nenad Spoljaric and Robert Jordan, Revised by: Thomas E.
Pickett
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| Physiographic Map of
Pennsylvania, Pennsylvania Geological Survey |
Yes, right in o
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| Nearly microscopic
garnets at BSP |
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Close-up of tiny garnets at BSP |
| Photos by Ken Casey |
As BSP is adjacent to our clubhouse at
Historic Greenbank Mill,
and drillin
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University of Delaware
Delaware Geological Survey
Open File Report No. 38, June 1995
Data Report on Rock Cores from Red Mill Road, Harmony Road,
Prices Corner, and Newport, Delaware
DGS ID: Cc13-17 SAMPLE NO.: 24896 QUAD: WIS
FIELD NO.: S-8-1 DATE ENTERED: 3/3/93
LOCATION: Prices Corner - core, 66' (58' ASL)
ROCK UNIT: Wilmington Complex ORIENTED SEC.:
STAINED: K-feldspar: Y Plagioclase: Calcite: Cordierite:
LITHOLOGY: Biotite gneiss
MAJOR MINERALS MODE (%) ACCESSORY MINERALS
quartz 38.0 zircon, apatite
plagioclase 38.0 monzanite halos in biotite,
biotite 22.0 colorless to yellow
garnet 1.0
opaques 1.0 RETROGRADE MINERALS
sillimanite mats x
Pale green mineral with opaques
NUMBER OF POINTS COUNTED: 400
COMMENTS
The rock in this core is a fine-grained dark biotite gneiss with
biotite grains aligned vertically.
FABRIC AND TEXTURES
Plagioclase: Equant xenoblastic grains, partial twinning,
round inclusions of quartz and plagioclase
Quartz: Undulatory extinction; large subgrain boundaries with
lobate edges
Biotite: Pleochroism is light brown to dark brown; laths have a
preferred orientation and are aligned to define the foliation
Garnet: Tiny xenoblastic to subidioblastic garnets grow over
other grain boundaries; some with small inclusions of opaques;
one garnet is elongated in the foliation
Opaques: Irregular shapes; two different opaques; in
reflected light, one is dark and the other is silver
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The fabri
(Source:
http://www.udel.edu/dgs/Publications/pubsonline/report38/31.html)
If you like the smalle
If,
As the
Delaware Greenways Project expands,
we’ll be able to hike directly to other geologic locations
rather efficiently on future MOTM fieldtrips. Thanks to the State of
Delaware and its partners, our educational
and recreational experiences will be enhanced.
Now, to the park-at-hand. Follow me.
I’ll guide us with the
DGS's GeoAdventure directions, so that we
may tread lightly, and leave the squirrels and woodpeckers to their
business. Don't worry, we'll see garnets!
| Rocky Run at BCSP |
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Boulder field at Rocky
Run, BCSP |
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Close-up of garnets in matrix |
| Photos by Ken Casey |
"To see the contact, you need to follow the stream to the confluence
of Hurricane Run and Rocky Run
and stay on the northeast side of Rocky
Run. (E,
Figure 2). The exposed contact is difficult to recognize
and probably interesting only to geology students at the high school or
college level. It is exposed in a ten
foot area along the northeast side
of Rocky Run where dark, fine grained
Wilmington Complex
gneisses are
interlayered with light colored Wissahickon gneisses. The
Wissahickon rocks appear to have been melted
and recrystallized to form
granites with thin layers of garnets. The biotite and sillimanite that
occur in the
Wissahickon gneisses are replaced by tiny garnets. This
reaction in which garnet replaces biotite and
sillimanite occurs only at
very high temperatures. The
Wilmington Complex
layers vary in thickness between
3 inches and 2 feet, and are dark
solid, massive rocks.”
(Source:
http://www.udel.edu/dgs/Education/bluerocks.html)
Let's zoom in on our gneiss garnets.
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| Large red garnets in
Rocky Run rock, BCSP |
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Closer view |
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Closest view |
| Photos by Ken Casey |
Now that we have sampled views of some of the largest
garnets in Delaware, let's have lunch. I'll trade
you an extra pomegranate for half of your peanut butter and jelly
sandwich. We can discuss other garnet
experiences over dessert, if you like.
Of course, our club visits collecting sites
for garnet all around our area. Please do inquire upon how to
join us as members, and can benefit from
our
club fieldtrips. Our trips our
setup and led by our own Bob Asreen,
Geologist, and Vice-President of Fieldtrips.
(Top): Gem Trails cover by Mark Webber
(Right): Close-up of Wissahickon Valley garnets in schist matrix
from Fairmount Park |
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Gem Trails of Pennsylvania and New Jersey
by Scott Stepanski and Karenne Snow, suggests that very small,
nicely faced, and deep red Almandine garnets may be found weathered out
of their host schist at Fairmount Park, Philadelphia. This author
visited there about three years ago, and found small quantity on the trail--enough
to fill a thimble or two.
I was fortunate enough to meet Ms. Snow a couple
of years ago at one of the Cape-Atlantic Rockhounds
events. She was kind enough to sign my copy of her book. I
think it brought me luck, since I've had some
good experiences collecting from locations that she and Scott Stepanski
had recommended.
These
Wissahickon Valley garnets may be collected
from Fairmount Park in Philadelphia. According to the book, garnets wash
out of the surrounding schist, to be collected on the trail.
Good
Luck!
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If
Our MOTM format will continue to offer us
information on two places we can visit to learn more
about minerals, such as this month's
As Delaware quartz occurs in commerical quantities
as gravel and sand, these easily accessible
forms are readily used in construction and landscaping. Our large
stretches of bay and ocean
beaches are for recreation, and as nature preserves.
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Exposed garnets from
Brandywine Creek State Park, 2004
Perhaps by now, they are eroded out--who knows?
(Photo by Ken Casey) |
Pyroxenes (and amphiboles), Tourmaline and Garnet (UC Berkeley)
Woodlawn
Quarry: A GeoAdventure in the Delaware Piedmont
http://webmineral.com/data/Almandine.shtm
http://www.rbmason.ca/databank/mineral/garnet.html
Delaware Minerals List
at mindat.org
Here is where DMS Members can add their Delaware
Quartz photos to share
with us.
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Almandine on Muscovite,
crystal 2.4 cm x 2.0 cm
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Almandine crystal, 2.6 cm x 2.1 cm
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| Almandine on Muscovite,
crystal 2.9 x 2.1 cm |
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Almandine crystal, 1.5 cm x 1.3 cm |
Until Next Time
We hope you have
enjoyed our historic visit to Delaware Quartz. Please join
us next month, for another article, and we shall journey together!
Until then, stay safe, and happy collecting.
Article Contributors
I would like to gratefully acknowledge
the generous contributions of our fellow Delaware
Garnet enthusiasts, collectors, authors, curators, professionals, and
club members who
made this work possible.
Thanks.
Arthur Koch, DMS Member, B. S. in Geology,
Mineral Photographer
Nenad Spoljaric and Robert Jordan, Thomas E.
Pickett, Delaware Geological Survey
Gem Trails cover by Mark Webber
©2008 All contributions to this article are covered
under the copyright protection of this article
and by separate and several copyright protection(s), and are to be used
for the sole purposes of
enjoying this scholarly article. They are used gratefully with
express written permission of the
authors, save for generally-accepted scholarly quotes, short in nature,
deemed legal to reference
with the appropriate citation and credit. Reproduction
of this article must be obtained by express
written permission of the author, Kenneth B. Casey, for his
contributions, authoring, photos, and
graphics. Use of all other credited materials requires permission
of each contributor separately.
Links and general contact information are included in the credits above,
and throughout this article.
The advice offered herein are only suggestions; it is the reader's
charge to use the information
contained herein responsibly. DMS is not responsible for misuse or
accidents caused from this
article. All opinions, theories, proofs, and views expressed within this
article, and in others on this
website, do not necessarily reflect the views of the Delaware
Mineralogical Society.
Suggested Reading:
Delaware Piedmont Geology including a guide to the rocks of
Red Clay Valley
by Margaret O. Plank and William S. Schenck
Gem Trails of Pennsylvania and New
Jersey by Scott Stepanski and Karenne Snow
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About the Author:
Ken is current webmaster of the Delaware
Mineralogical Society.
He has a diploma in Jewelry Repair, Fabrication &
Stonesetting from the Bowman Technical School, Lancaster,
PA, and worked as jeweler.
He has also studied geology at the University of
Delaware.
And, he is currently a member of the Delaware
Mineralogical Society and the Franklin-Ogdensburg
Mineralogical Society. E-mail:
kencasey98@yahoo.com.
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Invitation to Members
Members,
Want to see your name in
print? Want to co-author, contribute, or
author a whole
Mineral of the Month
article? Well, this the forum for you!
And Members, if you have
pictures, or a story you would like to share,
please feel free to offer. We'd like to
post them for our mutual enjoyment.
Of course, you get full photo and author credit,
and a chance to reach other collectors,
hobbyists, and scientists. We only ask
that you check your facts, give credit where it
is due, keep it wholesome for our Junior Members
watching, and keep on topic regarding
rockhounding.
You don't even have to be
experienced in making a webpage. We can
work together to publish your story. A
handwritten short story with a Polaroid will do.
If you do fancier, a text document with a
digital photo will suit, as well.
Sharing is the groundwork from which we can get
your story out there.
Our
club's webpages can reach any person surfing the
net in the world, and even on the International
Space Station, if they have a mind to view our
website!
We
are hoping for a possible tie-in to other
informative programs upon which our fellow
members might want to collaborate. Contact
any officer or board member with your
suggestions.
Our next
MOTM
will be a surprise.
For 2008, we are waiting for your suggestions.
What minerals do
you
want to know more about?
____________________________________
Most of the
Mineral of the
Month
selections have come from most recent club
fieldtrips and March Show Themes, and from
inspriring world locales, and suggestions by our
members, thus far. If you have a
suggestion for a future
Mineral of the
Month, please e-mail me at:
kencasey98@yahoo.com, or tell me at our
next meeting.
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