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                           Mineral of the Month--April

                              Delaware Feldspar


                                       Potassium Aluminum Silicate



                                        "Delaware Feldspar: Orthoclase"

                                              By Ken Casey

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

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        Delaware State Flag

Image courtesy of Marchex, Inc.
2007, World Flag Database

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Feldspar (or fieldrock)... Delaware, we have all kinds!

(Top, left & right): Delaware Orthoclase Feldspar, WCCSP
Photos by Ken Casey 2004


     This month, we explore in our own backyard: Delaware Feldspar.

     Well, we've been around the world on our quest for noble Fluorite.  Yes, it's time to come
home.  So, let's find out what's in our own backyard!  Everyone, everywhere, please join us! 

Let's go!



     Welcome back to our newest installment of Mineral-of-the-Month! 

     Spring is here!   It's now time to begin our outdoor fieldtrip season in Delaware.

     We'll not venture far from our clubhouse this day.  A short club bus trip is in order.
So, grab you backpacks.  We'll have a picnic lunch and nature hike in Newark, then
return to our clubhouse in Wilmington.  Enjoy!


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Path to bridge over the White Clay Creek Entrance to White Clay Creek State Park
Photos by Ken Casey


Why Delaware Feldspar?

     Well, Delaware Feldspar is one of the easier state minerals to understand and to find in
outcrops.  It is one basic constituent of our piedmont pegmatites, and more.  Members of the
Plagioclase Albite-Anorthite Group occur in and around Wilmington; whereas among geologic
settings all throughout western New Castle County, Orthoclase predominates.  Other pegmatite
minerals include: Muscovite, Garnet, Beryl, and Quartz. 

     Yes, even our state mineral Sillimanite can occur with Potassium or "K-feldspar".


     And, there are several varieties to cover.  From microscopic labradorite in Iron and Chestnut
Hills gabbros to Rockford Park gneiss and the large, coarse white feldspar of Woodlawn's
pegmatites, there is so much feldspar choices to visit in Delaware, that more than one article
would be required to discuss them all!  Therefore, we will visit one type in this time's MOTM
installment, Orthoclase feldspar, and leave the others for future essays.

Netscape users just click on picture to activate your Media Player (.AVI, 2MB)

     It's bright orange appeals to the eye, and can be easily seen in stream boulders at White Clay Creek State Park, for example.  This rich potassium feldspar also appealed to crafters and local manufacturers earlier in Delaware and nearby Pennsylvania's clay pottery and ceramics industries.  More on that later.

Stream boulders of feldspar in the White Clay Creek

Video by Ken Casey



What's in a name?


     The word "feldspar" derives from the German word for "fieldstone".  Farmers would clear
these stones from their fields upon tilling the soil in preparation for plowing.  It is a common
usage for any rock found there, regardless of its origin or chemical composition.

     Mineralogically speaking, most feldspar, being a common rock anyway, was found to have
a set of common properties, being either rich in either potassium (K) or Sodium (Na)--and every
proportion in between.  Orthoclase, or Potassium feldspar's name comes from the Greek words
"orthos" and "kalo", meaning "right" and "I cleave".  The name describes K-feldspar's good
cleavage at right angles.

     The IMA grandfathered the name before 1959.


     So, on today's fieldtrip, we will discover rocks bearing the Potassium end of spectrum in the
fields of Newark, Delaware.

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View of field and creek from bridge Lots of feldspar weathered rocks in the creekbed
Photos by Ken Casey


Chemistry & Science


     Now that we know we've heard the early usage of the term, let's define what modern
geology defines as a feldspar.

Feldspar - Any of a group of crystalline minerals, all silicates of aluminum with either potassium, sodium, calcium, or barium. An essential constituent of nearly all crystalline rocks.


Feldspar -Silicates of aluminum, containing sodium, potassium, calcium, or barium or combinations of these elements. Clay is the chief substance formed when weathering decomposes feldspars.



     Containing potassium, orthoclase is an alkali feldspar.   It can be found in granites, felsics,
trachytes, and pegmatites.  "Orthoclase is the characteristic potassium feldspar of igneous
rocks, occurring both alone and in perthitic intergrowth with albite; it also occurs in some
metamorphic rocks."


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Orange Orthoclase in pegmatite, WCCSP Feldspar and granite rocks in creek, WCCSP
Photos by Ken Casey

     Delaware' metamorphic Amphibolite contains Amphibole and Feldspar.  This rock derives
from our rich volcanic past.


     Delaware has orthoclase in its biotite gneiss and in other settings. 


     According to Delaware Piedmont Geology, orthoclase is a common constituent here.  Also, the
Red Clay Valley contains intrusive granite composed of quartz, orthoclase, plagioclase, and mica
or amphibole in coarse grains.

     A favorite source,, states in its database that orthoclase is found among the
gabbros of the defunct Brandywine (Hubbard) Quarry in Wilmington.

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Close-up of Orthoclase in granite, WCCSP More Orthoclase, WCCSP
Photos by Ken Casey

     And, the Water Resources Agency at the University of Delaware quotes Plank et al. (2000),
stating that "[w]ithin the [Wissahickon] formation are coarse-grained igneous bodies known as
pegmatites, composed of mica, feldspar and quartz..."


     Generally, feldspar's non-porous texture may be due to slow growth.  Might this affect our local
clay's qualities--maybe.






     Potter's clay contains feldspar.  Delaware clay is no different.  From Red Clay Creek
to White Clay Creek, and in most streams in between, much of our natural clays in New
Castle County may be used to make pottery.  In fact, feldspar and clay have been mined
for industry for over two centuries, and perhaps into to the paleo-people's dawn for millennia:

     "Born of a prosperous Quaker family, William Ellis Tucker [1800-32] began in 1826
his earnest experiments [p. 413] in porcelain making, at the old Waterworks building in
Philadelphia. That year he bought [in brief partnership with one John Bird] a property
near Wilmington, Delaware, that yielded feldspar, and another at 'Mutton Hollow in the
state of New Jersey' that provided kaolin or blue clay. In 1827 his porcelains won a
silver medal at the 4th Franklin Institute exhibition, and in 1828 another, for ware
comparing with 'the best specimens of French China'."


     Pottery was first used in Woodland I times by the Delaware paleo-Indians in areas
such as Augustine Creek and Odessa.  Perhaps they crafted their vessels from local clay.


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The clay of White Clay Creek, WCCSP Imagine mining clay here 150 years ago
Photos by Ken Casey

     In more modern times, red orthoclase was crushed and incorporated into ceramic
formulae.  Some of this feldspar weathered to high-quality clay.  Dr. William J. Ullman,
Professor of Oceanography and Geological Sciences of the University of Delaware,
Lewes, has published work on the weathering process of feldspar, sometimes into clay.


     For example, local feldspathic, coarse-grained granites decompose in Kaolin clay:

“The celebrated deposits around Hockessin are of this character. Dixon ’s quarry
near Wilmington has produced very fine yields of feldspar. A very notable vein cuts
across the road leading up the Brandywine, about one and a half miles from the
head of the State. Its width is about twenty feet, and the material a mixture of red
orthoclase albite, blue quartz and muscovite. The rock is quarried for the valuable
feldspar, used in the manufacture of artificial teeth....”


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Decrepitating Orthoclase into Clay at WCCSP Ground red clay ready for brick-making
Photo by Ken Casey Photo Courtesy of

    In nearby Delaware County, Pennsylvania, "[e]xtensive mines of kaolin are worked
at the West End of the county, and an outcrop of pure feldspar rock in Concord
Township is exploited for use of dentists. (See numerous heliotype views of the Kaolin
mines in Report C5.)


     I am not sure if clay is mined today in these areas; however, with special permission,
maybe, one could sample these clays as specimens, or take to use in a ceramics project.




     Just about every mineral has a metaphysical use these days--most of which are positively
employed in healing.

     According to the folks at the Foundation for Balance and Harmony, orthoclase has a good

"Metaphysically, Orthoclase Feldspar has a pleasant, refined energy.  Orthoclase Feldspar
can help overcome tragedy, as well as aligning the chakras and meridians of the physical
body.  Known as the "stone of cooperative effort," Orthoclase Feldspar encourages
cooperation among individuals and offers insight into group experiences.  Orthoclase
Feldspar can help one find new and unconventional ways to obtain goals, and is said to
foster connection to the wisdom of ancient Egypt."


     Since the geology of Newark, Delaware consists of surficial stream deposits of salmon
orthoclase and its resultant clays, perhaps the good vibes experienced on the University of
Delaware campus are due to the happy influence of this colorful feldspar.

earth_3D_magnetic_field_structure.jpg (69643 bytes)      As basis of my informal theory are the studies of Earth's magnetic fields.  Some scientists have hypothesized that the associated strong fields hovering over iron deposits do influence societal behavior at large.  For example, many world famous battlefields have been proven by geophysical surveys to be located over such metallic underscoring as a temporary weakening in the localized magnetic field occurs.

(Source: Professor Phil Callahan, Paramagnetism)

3-D Model of Earth's Magnetic Field
(Graphic Courtesy of NPACI)

     I would suggest that locally, the conflict at Old Cooch's Bridge (September 3, 1777) in
Newark foots the bill.  In addition, other area Revolutionary War battlefields, like the Battle
of the Brandywine
at Chadd's Ford, Pennsylvania (September 11, 1777), might serve as a
large-scale example. 

starsandstripes1777.gif (1641 bytes)      Though the U. S. Army suffered defeat at both engagements, our Newark fight is cited as the first time we flew the Stars & Stripes into battle.  Our impetus to fight for freedom grew greater from there.

"Betsy Ross Stars & Stripes" Flag, adopted by
Congress on June 14, 1777
(Graphic courtesy of American Flag & Gift

     On the more peaceful side, the modern town of Sedona, Arizona, attracts those who
search for a greater healing energy.  Check out Sedona's live red rocks web cam, and see
how you feel.  Some have noted that "Sedona" spelled backwards is "anodes", or a technical
term related to the transmission of magnetic fields and electricity.

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Sedona "Red Rocks Live" Cam, May 16, 2007

     Without scientific evidence, though, to support this idea, it is still a personal conjecture;
but, I thought I'd give it a mention to get your minds going.  Perhaps you'll study and write
on the focus of "geology and society".

     So, remember to keep your senses open to the affects of the geology and geography.  A
toponymic name might be a clue to a site's aspects.


Two Museums of Note

     We'll venture to a couple of nearby states for our museum selections for this month.  First,
we have the Perkins Geology Museum at the University of Vermont.  Admission is free, and a
one week prior reservation is required.  It's accessible when the University is in session.  Before
you go, why not visit their online Digital Archive for photos of specimens from their collections.

     Second, the Emerald Village & North Carolina Mining Museum of Little Switzerland, North
Carolina is more than just an old feldspar mine.  It is open for individual, family, and group tours,
and has opportunity to visit three old mines, a museum, gift shop, and to pan for gems!



     Either as stone for walls, pottery, ceramics, and dentition, or as a specimen or healing
stone, or as brick, this versatile, common mineral and clay can serve, even as much as the
enjoyment we derive from the beautiful park landscaping that we've seen today.



Ashland Nature Center junior digs for feldspar and other Delaware Treasures

White Clay Creek State Park

Delaware Clay Resources by Thomas E. Pickett, 1970

Delaware Nature Society "State of the Watersheds"

Chuck Bryant's White Clay Creek State Park Runner's Page

"Feldspar" from the North Carolina Geological Survey

"Feldspar Group" at

"Delaware, USA Minerals List at


Members' Gallery

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

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Pink Orthoclase Feldspar crystals from northern Wilmington, Delaware area
Photos by Ken Casey


Until Next Time

     We hope you have enjoyed our historic visit to Delaware Feldspar.  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




Photo & Graphics Credits

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


Marchex, Inc., World Flag Database

American Flag & Gift

Television Trust for the Environment

National Partnership for Advanced Computational Infrastructure

2007  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

Feldspar Minerals: Volume 2: Chemical and Textural Properties
by Joseph V. Smith

Feldspar Minerals: Crystal Structures, Physical, Chemical and Microtextural Properties by Joseph V. Smith and William L. Brown


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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:

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
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 or questions:

This page last updated:  January 17, 2013 09:16:48 PM




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