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                           Mineral of the Month--February 2008

                              Exotic Pegmatites, Part 1

                                                   Various and Sundry Minerals & Chemistries

                                                   At least SiO2 and other silicates


                                        "Exotic Pegmatites"

                                              By Ken Casey

Why Exotic Pegmatites?
What's in a name?
Chemistry & Science
Some Exotic Pegmatite Geology
Two Museums of Note
Members' Gallery
Article Contributors
Photo & Graphics Credits
Suggested Reading
Invitation to Members
Past Minerals of the Month


or a world globe

Image by Ken Casey


Exotic pegmatites...



(Top, left): , Wilmington, Delaware
Photo by Ken Casey 2008

(Top, right):
Photo by Ken Casey 2008



     Welcome back, faithful fieldtrippers!  This month, our Mineral-of-the-Month takes us all over
the world.  In this two-part series on Pegmatites, we'll scour the globe in search of some oddities
that make classic, gem, and exotic rock types that fall into this category.

     The weather around the world may vary, so dress in layers.  Let's go!




     Pegmatite is an igneous, coarse-grained granite rock. From the Greek pegma, meaning
“something fastened together“, a pegmatite is a rock made up of many minerals, such as
garnet, mica, and feldspar. Many other gems and minerals can join these three during a
pegmatite melt’s formation. In Delaware, we have blue and green beryls, kyanite, school
tourmaline, columbite, and more. In other parts of world, a large variety of gems can occur
in pegmatite, like aquamarine and emerald.

     So come on along, we have an Exotic Pegmatite 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 Exotic Pegmatites?


      Our local .  Please do join us!


     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?   




Pomegranate in cross-section   Small garnets in situ from Brandywine Creek State Park
Photo by Peter (Fir0002),   Photo by Ken Casey

     Much of




     The name “quartz” was grandfather prior to 1959 by the IMA.




Chemistry & Science

     Delaware's quartz is a silicate of chemical formula SiO2.  It

     On the Moh’s Hardness Scale, it ranges from 6.5-7.5.

Garnet sandpaper    60-Grit Garnet sandpaper   Garnet used to make sandpaper 
Photo courtesy of Grimes Industrial    Photo courtesy of Woodzone   Photo by Ken Casey 




     In the photos below,

 Photos of Appalachian mountains and plateaus overlooking Susquehanna River at Red Hill, Hyner, PA  (Photos by Ken Casey)

     Delaware has


         What .

(Source: )

Garnet-laden drill core samples
(Photo courtesy of Oliver Holm, Geoscience Australia)

     For example,

     Our Piedmont




Some Pegmatite Geology

     Gneiss is the primary


"The region of pegmatite dikes in the state of Minas Gerais in Brazil
has been the primary source of gem beryl and several other species of
colored gemstones for many years. Rivers have cut places through the dikes
and alluvial deposits, called "cascalho", which are scattered throughout
the region. It is notable that the extensive gemstone deposits in Minas
Gerais often yield large aquamarine crystals accompanied by all the other
colored varieties of beryl."

"Beautiful gem crystals have been recovered from such
unlikely places as water wells, drainage ditches, road cuts, and
excavations for building foundations."

"Most of the largest and finest aquamarines are from Brazil. Imagine
being able to see an object distinctly through the completely transparent
length of a 19 by 16 inch hexagonal gemstone prism weighing 520,000
carats! Such a crystal was unearthed by David Mussi in the Papamel mine
near Marambaia in 1910. Two Germans purchased the 110 kilogram
greenish-blue crystal for 35,000 marks. The gems cut from this gigantic
crystal were heat-treated in the first known successful application of
this method to remove the undesirable yellow tones and achieve a purer
blue color. Jaroslav Bauer and Vladimir Bouska wrote in their book,
Precious and Semi-precious Stones, that its yield of 200,000 carats of cut
gems supplied the world market with faceted aquamarines for several

Brazil, Madagascar, Siberia and Ural Mountains, Russia, India, Pakistan, Afghanistan, Namibia, Zimbabwe, Mozambique, Mt. Antero, Colorado, Maine, Connecticut, North Carolina, California.

C:\Users\Ken\Documents\Pegmatite\[Ganoksin] - Lets Talk Gemstones - Aquamarine - a cyclosilicate.mht



Almandite Garnet crystal Photomicrograph, South Carolina's Appalachian Piedmont    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


     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,


     According to DGS publication Delaware Piedmont Geology by Margaret O. Plank and William S. Schenck, “”




     More sp


     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

Physiographic Map of Pennsylvania, Pennsylvania Geological Survey

Microscopic Garnet


     Yes, right in o

Nearly microscopic garnets at BSP    Close-up of tiny garnets at BSP 
Photos by Ken Casey 

     As BSP is adjacent to our clubhouse at Historic Greenbank Mill, and drillin



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
LOCATION: Prices Corner - core, 66' (58' ASL)
ROCK UNIT: Wilmington Complex ORIENTED SEC.:
STAINED: K-feldspar: Y Plagioclase: Calcite: Cordierite:
LITHOLOGY: Biotite gneiss

quartz 38.0 zircon, apatite
plagioclase 38.0 monzanite halos in biotite,
biotite 22.0 colorless to yellow
garnet 1.0
sillimanite mats x
                Pale green mineral with opaques

The rock in this core is a fine-grained dark biotite gneiss with biotite grains aligned vertically.


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


    The fabri




xpl off of 1 edge of Garnet 10* (Almandite crystal thin-section)
(Photomicrograph by UCLA's Petrographic Workshop)

     If you like the smalle


Macroscopic Garnet


     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    Boulder field at Rocky Run, BCSP    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.”


     Let's zoom in on our gneiss garnets. 

Large red garnets in Rocky Run rock, BCSP    Closer view    Closest view 
Photos by Ken Casey 

Other Quartz Experiences

     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

     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!





Two Museums of Note

     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.

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

Delaware Minerals List at


Members' Gallery

     Here is where DMS Members can add their Delaware Quartz photos to share with us.


Almandine on Muscovite, crystal 2.4 cm x 2.0 cm

  Almandine crystal, 2.6 cm x 2.1 cm
Almandine on Muscovite, crystal 2.9 x 2.1 cm   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. hardhat2a.gif (5709 bytes)



Article Contributors

Delaware Piedmont Geology by Margaret O. Plank and William S. Schenck, DGS



Photo & Graphics Credits

    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. 

Arthur Koch, DMS Member, B. S. in Geology, Mineral Photographer

Marchex, Inc., World Flag Database

Delaware Piedmont Geology by Margaret O. Plank and William S. Schenck, DGS

Nenad Spoljaric and Robert Jordan, Thomas E. Pickett, Delaware Geological Survey

Physiographic Map of Pennsylvania, Pennsylvania Geological Survey

Photomicrograph by UCLA's Petrographic Workshop

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


KEN.JPG (31503 bytes)

   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:

Invitation to 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?

aniagate.gif (1920 bytes)


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:, or tell me at our next meeting.



Past Minerals of the Month
August 2007 Mineral of the Month: Schorl (Black Tourmaline)
July 2007 Mineral of the Month: Rubellite
June 2007 Mineral of the Month: Elbaite 
May 2007 Mineral of the Month: Delaware Feldspar, Part 2 
April 2007 Mineral of the Month: Delaware Feldspar: Orthoclase
March 2007 Mineral of the Month: "The Colors of Fluorite"
February 2007 Mineral of the Month: Pennsylvania Fluorite
January 2007 Mineral of the Month: Sillimanite
December 2006 Mineral of the Month: Hedenbergite by Karissa Hendershot
November 2006 Mineral of the Month: Brandywine Blue Gneiss
October 2006 Mineral of the Month: Spessartite by Karissa Hendershot
September 2006 Mineral of the Month: Native Silver
August 2006 Mineral of the Month: Kryptonite
July 2006 Mineral of the Month: Azurite
June 2006 Mineral of the Month: Pyromorphite
May 2006 Mineral of the Month: Tsavorite by Karissa Hendershot
April 2006 Mineral of the Month: Variscite
March 2006 Mineral of the Month: Petrified Wood, Part II
February 2006 Mineral of the Month: Petrified Wood, Part I
January 2006 Mineral of the Month: Strontianite by Karissa Hendershot
December Mineral of the Month: Clinozoisite
November Mineral of the Month: Bismuth
October Mineral of the Month: Wulfenite by Karissa Hendershot
September Mineral of the Month: Turquoise
August Mineral of the Month: Peridot
July Mineral of the Month: Ruby
June Mineral of the Month: Antarctic Fluorite
May Mineral of the Month: Dolomite, Part 2
April Mineral of the Month: Dolomite, Part 1
March Mineral of the Month: Calcite
February Mineral of the Month: Agate
January Mineral of the Month: Fluorite
December Mineral of the Month: Pyrite
November Mineral of the Month: Stilbite  
October Mineral of the Month: Celestite   


Comments and questions:

This page last updated:  February 19, 2011 10:15:12 AM




Next Meeting

April Program, Monday, April 8, 2013:

"Destruction of the Fossil Exposures in the Chesapeake Bay Area" presented by Dr. Lauck Ward

General Club Meeting:
April 8, 2013

We are meeting at
Greenbank Mill

Special Meetings:

*Show Committee Meeting, April or May, 2013

*New Home/Lapidary Committee, 2013

*Board Meeting,  April, 2013

Next Field Trips


Past Fieldtrips

Next Show
DMS March Show
March 1-2, 2014 at DelTech Stanton


Our 2013 Show Theme was:
"All That Glitters is as Good as Gold!"

March Show 2013 Report






Fossil Forum

"Dinny, the Dino"

"Belemnites are coming"


MOTM June also commemorates our 50th Show!

It's shiny, yellow, and is a symbol of 50 Years!Can you guess?


Collecting Adventure Stories:

"Sunny Brook Crick Goethite" by Joe Dunleavy