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                           Mineral of the Month--November

                              Brandywine Blue Gneiss

                                              (aka "The Wilmington Blue Rocks")

                                      Rock consisting of 4+ minerals

                                               Brandywine Blue Gneiss: From Volcanism to Underlying Delaware's Architecture

                                              By Ken Casey

Chemistry & Science
Mining Stories
Members' Gallery
Article Contributors
Photo & Graphics Credits
Suggested Reading
Invitation to Members
Past Minerals of the Month
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A rock still prevalent in the geologic...


...and social history of Delaware!

(Top, left):Blue Gneiss
Photo by and courtesy of Ken Casey 2006

(Top, right): Blue Gneiss dry-stack wall
Photo by and courtesy of Ken Casey 2006


     This month, our quest is to find instances of a key Delaware rock: Brandywine Blue Gneiss.

     Yes, you say that this gneiss rock is not a mineral, but a compilation of several minerals. 
I agree with you.  I tried to figure out a forum for rocks, and since we already have our own
Mineral-of-the-Month and Fossil Forum, adding a "rocks only" area might be redundant.  All
this, especially since we have set a precedent for already studying some minerals along with
their associated minerals and matrices.

     So, why not trek around colonial Delaware a bit, and expand our horizons with a bit of history,
architecture, and the modern "blue rock". 
Let's go!



     Welcome to another Mineral-of-the-Month installment! 

     This month, we add some local flavor to our tour.  Our club's home state of Delaware is
richly steeped in some important local, national, and international history.  Along with our
native blue gneisses, we will explore their primary use in building a nation.

     Owing to the vastness of local architecture available to us, we shall visit a few key places,
along with a brief history of quarrying and modern road building.  Enjoy!


Chemistry & Science

     Our Brandywine Blue Gneiss has four main mineral constituents: Quartz, Feldspar,
Pyroxene, and Magnetite.  Some additional variations in our area can contain: Orthopyroxene
and Garnet.

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Drill hole for blasting Closeup of Blue Gneiss minerals

Photos from the Blue Ball Project Construction Site by Ken Casey

     According to geologists of the DGS and USGS, "[t]he amphibolites and 'blue rocks' of the
Wilmington Complex were formerly a volcanic island that existed seaward of the ancient North
American continent about 500 million years ago."

     More specifically, "[t]he age of the Wilmington Complex is controversial; however, a large
mass of granitic rock, exposed in the community of Arden, was radiometrically dated and found
to be approximately 500 million years old. This date suggests the Wilmington Complex may
represent the root zone of the volcanic arc that existed off the ancient North American continent
during Cambrian and Early Ordovician time, between 543 and 480 million years ago."

(Source: "America's Volcanic Past: Delaware", USGS)

IMGP0302.JPG (584195 bytes)Freshly-blasted blue gneiss surface

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Photos by Ken Casey

     Though it may be one-half billion years old, the fresh-cut stone is a shimmering dark blue.  Upon weathering, it darkens to a deep gray-black.  This author was born right near an outcrop, and got to happily pass his birthplace en route, in order to collect our club's samples.

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50-year old roadcut view of I-95 in Wilmington

     About the stone, geologically, it is believed to be about 570 million years old.  It was formerly
referred to as a ‘blue granite’ by quarrymen in centuries past, but is technically a metamorphic,
banded blue gneiss of the Wilmington Complex.  The rock is composed of quartz, feldspar,
pyroxene, and magnetite, and began its existence from ancient volcanoes, which preceded the
Appalachian Mountains orogeny (or mountain-building event).  Over time, it recrystallized into a
solid, stable building stone, still useful in today’s architecture.


Integrity & Physical Properties of the Wilmington Blue Rock

     It chips, when broken.  Some sharp edges result.  Specimens should be trimmed to prevent
cuts.  This blue stone is unfriendly to all but the most powerful and loud rock crushing mills. 
Round, eroded rocks are ever plowed from farmer’s fields.   When hewn with masonry chisels
and hammers, it serves well as dimensional stone.

     I would imagine that it passes modern engineering stress tests, as it is still used today in
projects, when available.  And, in our mild, occasionally earthquake prone area, historical
structures have stood throughout centuries of Delaware's episodic seismic activity.

IMGP0191.JPG (343124 bytes) Our club has samples available to teachers with limited quantity.  We may have some to offer
at our March 3-4, 2007 Show.




     The major use for our specialty Wilmington Blue Rock is as dimensional stone.  Many
important historical structures were built from locally quarried rock, and still stand today.

     Our focus here will be on the architectural and historical uses in Wilmington, Delaware. 
There are too many instances to offer in this installment.  I'll leave it to you to surf the links
I've listed to plan your own virtual and actual trips.

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Historical Masonry Wall, Lombardy Estate/Cemetery Modern dry-stack Wall, Ronald McDonald House

Photos by Ken Casey


IMGP0322.JPG (424809 bytes)A. I. DuPont Children's Hospital Gate


Old Swedes Church, Wilmington
A. I. DuPont Children’s Hospital Wall
Gunning Bedford, Jr. House on Route 202
Fort Christina State Park: Delaware’s Plymouth Rock
Kalmar Nyckel--The Tall Ship of Delaware
Washington Monument Memorial Stones--Delaware
Brandywine Creek State Park (near my birthplace)
Weldin Plantation
Gravestone Markers & Other Monuments
Fenceposts, wall, and boundary markers
Gettysburg Delaware Monument?
Many Other Places


IMGP0318.JPG (430257 bytes) Modern

Blue Ball Project
Ronald McDonald House Wall
Wilmington College, Small Building
Interstate-95 through Wilmington
Mollyockett Motel, Woodstock, Maine

Ronald McDonald House new dry-stack wall


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IMGP0316.JPG (551698 bytes) Modern landscaping makes use of excess site deposits for beauty and against waste.

(Top, left & right: The Nemours Clinic)

(Below, left: Dry-stack Wall at the Ronald McDonald House)

Photos by Ken Casey


Traveling Blue Rocks

     Blue Rocks are now known to travel two ways: one, as our local minor league baseball team
on the road; and, two, as a parcel mailed by this author to Tim and Fran Buck of the Mollyockett
, on behalf of DMS.  (Yes, even the ball club's logo has a rock pick hitting some blue rocks!)

     On the first account, I am not sure if Frawley Stadium incorporates any Brandywine Blue Gneiss
in its construction, or not.  I would be pleasantly surprised to know that it did.   Symbolically, their

     On the second account, one masonry-quality stone with a fresh blast surface made its way
by USPS Priority Mail to a rockhound haven in Woodstock, Maine.  The Bucks intend to add it
to their soon-to-be-constructed fireplace in a novel restaurant and renovation project.

     Our club got the opportunity to share this aspect of our club’s home state with Tim and Fran.  Rockhounds from around the country and world can visit, and in one place witness the variety of
rocks and minerals from all 50 States!

     This author has only seen such assemblages in major museums and at national monuments.

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Washington Monument Memorial Stone--Delaware
Courtesy of the National Park Service
Washington Monument
Photo by Jeff Tinsley, Smithsonian

     The stone might serve as a humble cornerstone on their new Crosstone Restaurant’s fireplace. 
We have also sent a smaller sample for them as a keepsake.

     As one of 50 such stones, each representing a state in our nation, our blue rock will give
testimony to Delaware's rockhounding community.  Tim and Fran's Mollyockett Motel lies in the
heart of Maine's rockhounding country in Oxford County.  If you plan to visit:

The Mollyockett Motel
Tim and Fran Buck

1132 S. Main St.
Woodstock, ME 04219


Within a Mile of the Blue Ball Project

     The particular stone that this author sent to Maine has a story.   Regarding the significance
and history of this stone, I’ll tell you how and where I obtained it first.  With permission from the
generous folks at the Delaware Geological Survey and DelDOT (The Delaware Department of Transportation), I got to collect from the spoils piles of newly blasted road construction work at
our new mega-intersection of U. S. Route 202 and Foulk Road.

     Also on the site is an historic dairy barn, called the Blue Ball, having a boundary marker post
with a painted blue ball atop it, which acted as a "carriage stop" and landmark to travelers.  When
The innkeeper raised the blue ball, the coachman knew to stop.  If he lowered it, the driver knew
to keep going, similar to our modern bus stop. 

     The barn itself served on the Alfred I. DuPont estate for some time, before sadly being left
derelict for decades (40+ years in my memory).  It is now being restored to special use.

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From this... ...and this...

IMGP0313.JPG (254560 bytes) (Top, left & right: Blue Ball Project Construction)

(Bottom, left & right: Highway Project Phase Completion)

Photos by Ken Casey

IMGP0312.JPG (456454 bytes) this... ...and this

     After ten years of archaeological digs, the site became open to road improvements.  The state
is currently developing the surrounding area as fully-accessible parklands.  To see the project’s
progress, go to

     It is at this opportune time that I could get permission to obtain samples for the Bucks and
for our club’s educational outreach program for teachers, scouts, and fellow rockhounds.


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Historical Marker for Gunning Bedford, Jr. Estate "Lombardy", the Bedford Estate

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Historical Marker closeup Masonic Lodge sign at "Lombardy" Estate/Cemetery

Photos by Ken Casey

     As for our area's history, quite a few famous people lived nearby, some of whom had crafted
their homes from this illustrious blue rock.  One such personage is Gunning Bedford, Jr.  He was
instrumental in both Delaware’s and our nation’s history, by serving as a delegate to the U. S.
Constitutional Convention in 1787.  His home stands just a few hundred feet from our collection

     The centuries old trail that passes by his house, which became a nearby highway, laid claim
to the passing of our patriot, Caesar Rodney, who rode his horse 80 miles almost non-stop from
Dover (our capital) to the city of Philadelphia.  He was to be the first representative to break the
deadlock vote in favor of the Declaration of Independence on July 1, 1776.  He and his trusty steed
trotted over the local blue rock, and passed by farmer’s walls and homes constructed of our famous

     To this feat, the abutting property, which houses a shopping mall, gives tribute by being named
"Independence Mall".  It's veneer architecture is reminiscent of the original building in Philadelphia.

     More recently, our own Carolina League baseball team is named after this resilient stone--The
Wilmington Blue Rocks.  Check out the
ball club's logo for clues to this tribute.

     It is a tough stone, once quarried and used to construct many of Delaware’s historic buildings,
like Old Swedes Church in Wilmington.  Near the church, a half-century old blasted outcrop lines the
shoulders of Interstate 95, which also passes near Maine's doorstep, as well.  No more stone quarries
exist to supply this dimensional stone

     The credit for obtaining such a stone (as you know it is hard to come by these days) should go
to William Schenck and Tom McKenna, Geologists of the Delaware Geological Survey, Vernon
Lawton and Nick Hetrick, Project Engineers of DelDOT, and Bruce Kay of DMJM Harris, Inc.,
Contractors, and of course, most humbly, the Delaware Mineralogical Society.   Thanks!

[Adapted from the letter I researched and wrote to send with with our State's contribution.]



Mining Stories


     Local archeologists plot the earliest evidence of man inhabiting northern Delaware as being
marked at about 12,000 years ago, during the Paleoindian Period.  Though we have some
interpretation of rock use spanning up through mid-seventeenth century colonial times, only
arrow and spear points, and mortar and pestle stones are the primary usages.  No mining was

  (Source: DelDOT Projects: Archaeology - Prehistoric Archaeology)

     There may be evidence that the earliest natives to this area employed the Brandywine Blue
Gneiss, but this author has not yet come upon it.  I can suggest that some Delaware Paleoindians
may have witnessed the beauty of those boulders strewn across the Brandywine Creek as a result
of erosional processes in ancient times.

    Unbeknownst to passengers of the Kalmar Nyckel, early Swedes who disembarked at the site
of Fort Christina on the Christina River, stepped across a large ledge of blue rock.   One could
suggest that this was the "Plymouth Rock" of Delaware.  Their foothold into the New World was
literally here.  One wonders if the thought crossed their minds to seek out this stone for future
use, either symbolically or practically.

     In fact, if you look at our club’s website banner above, you might make out a small masted
ship on the water.  That is the Kalmar Nyckel--symbol to us in Delaware of exploration.  Our
club motto captures this sentiment as we translate it from Latin to English.  The three words
"Omnem Movere Lapidem" work out to "No Stone Unturned".

     Since the 1630s, European explorers and colonists witnessed some of the earliest stone
structures in use.  As they tilled the soil, and loosened the blue rock fieldstones, they began
to accumulate excess stone.  This hard-to-work rock found its way into property boundary walls
and some building foundations.  Some of these walls still stand today, crisscrossing the county.

     After discovering that our blue rock lends itself well to masonry work, institutional buildings
and homes were modeled after its quaint character.  The Old Swedes Church and patriot
Gunning Bedford, Jr's house in Wilmington are both constructed of this hefty stone.

     The DuPont family's endeavors at gentrifying the landscape proved successful with the use
of this resilient rock.  Their business buildings made use of this locally quarried resource.  Homes
and mills alike stood proudly, some have said haughtily, against the background of Delaware's
rich history.  Today, we take pride in the vast accomplishments of our early residents.  Now, many
current residents rely upon the DuPont Company's centuries old foundation to help drive the
economy of Delaware, and serves to underlie Delaware's society and culture.

     Most of these magnificent structures still stand today, giving testament to the tenacity of
this stone's hold on our character.  Many of the historic places may be visited by us with only
a museum's invitation awaiting our reply.  (See below, for a list of museum links)

     In the past, it was quarried commercially in the nineteenth and early twentieth centuries.  As
the most prolific, local building stone, this "Blue Granite", as it is sometimes called, served in
the construction of various landmarks, public spaces, and utilitarian structures.

     Quarries in Brandywine Hundred, New Castle County, Delaware operated with blasting going
on within the city limits.  One such hazardous event in 1902 at the Brandywine Granite Company
quarry injured an Italian stoneworker.  The quarry was then closed.

(Source: Stone Quarries and Beyond by Peggy B. Perazzo and George P. Perazzo)

     Modern mining in the twenty-first century was conducted as the result of a need to remove
excess material from a large road expansion project.  The Blue Ball Project encompasses not
only highway construction, but reuse of abutting land, while optimally preserving our state's rich
history and architectural past.

     Though most of the project bedrock was blasted away to be reburied on site, much is seeing
its way toward some visible usefulness.  Three examples are: overpass stone veneers, local
institutional drystack walls, and rip-rip for project drainage areas.  For further beautification, some
hefty landscape boulders will grace the Delaware Greenways and onramp overlooks, which add
modern history to the Wilmington Blue Rocks' usefulness.

     This author shares the view that with a vastly populated Delaware, no future blue rock mining
will be permitted, especially that done by blasting.  So, if you have a good sample of Wilmington
Blue Rock--hold on to it!  Show it to others to educate them about our past.   And, Enjoy!




State of Delaware Division of Historical & Cultural Affairs

Historical Society of Delaware

Brandywine Creek State Park

The Wilmington Blue Rocks--Delaware Geological Survey (DGS)

The Hagley Museum and Library, Wilmington, Delaware

Old Swedes Church, Wilmington, Delaware

DelDOT Projects: Archaeological Exploration and Historical Preservation in Delaware

Delaforum's Blue Ball Photo Album

The Mollyockett Motel, Woodstock, Maine (Blue Rock in Fireplace masonry)

Delaware Greenways

Delaware Department of Natural Resources & Environmental Control (DNREC)


Members' Gallery

Here is where DMS Members can add their nice Gneiss photos to share with us.


Until Next Time

     We hope you have enjoyed our pleasant visit to Brandywine Blue Gneiss.  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

United States National Park Service (NPS)

Margaret O. Plank & William S. Schenck, The Delaware Geological Survey

United States Geological Survey Cascades Volcano Observatory, Vancouver Washington (CVO/USGS)

Delaware Department of Transportation (DelDOT)

The Blue Ball Project

DMJM Harris Construction, Inc.

The Mollyockett Motel, Woodstock, Maine

The Wilmington Blue Rocks Baseball Team

U. S. Department of Transportation, Federal Highway Administration: A Benchmark for Livable Progress

Stone Quarries and Beyond by Peggy B. Perazzo and George P. Perazzo


Photo & Graphics Credits

I would like to gratefully acknowledge the generous contributions of our fellow Gneiss
enthusiasts, collectors, authors, curators, professionals, and club members who made this
work possible. 

United States National Park Service (NPS)

Jeff Tinsley, Smithsonian Institution

2006  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



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 2007, we are waiting for your suggestions.  What minerals do you want to know more about?

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Most of the Mineral of the Month selections have come from most recent club fieldtrips and March Show Themes, and from inspriring world locales. 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
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   

This page last updated:  February 19, 2011 10:14:49 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