month, we explore in our own backyard: Sillimanite.
"The official State Mineral of Delaware" by vote of our Legislature, this
had initially captured the attention of our club in 1977. It's story lies
herein. Let's go!
Welcome to this
year's first installment Mineral-of-the-Month!
This January, we
will uncover what makes Sillimanite so popular to our residents, and some
items on it's formation in Delaware, and in general.
We seem to have formed a fondness for this
simple silicate. I'll share with you why we like
it so much. Enjoy!
|| Benjamin Silliman was more than just a mineralogist whose career merited his name
being lent to a new mineral. He was accomplished in science, the law, and education,
all of which drove his ambitions. As one of the first American professors of
science at Yale, he began lecturing on chemistry in 1804, when Thomas Jefferson, our third
President, resided in the new White House in Washington, D. C. There were 15 stars
on the flag and States of the Union. And, the ink on the 1803 Louisiana Purchase
document was still fresh. Our early days of a national science were ready for many
(Left): Portrait of Benjamin Silliman, Sr.
courtesy of wikipedia.org
amazing firsts propagated his fame even more so. He was first to
petroleum distillates, first to publish a scientific account on American meteorites,
and first to
discover new minerals and compositions. We still marvel at most of these phenomena
Silliman founded the American Journal of Science (1818), and was named by the
U. S. Congress to membership in the National Academy of Sciences as a Charter Member in
1863. (Source: "Founding
of the National Academy of Sciences", NAS website)
|Silliman statue at Yale
courtesy of wikipedia.org
||15-star U. S. Flag at the time
of Silliman's first lecture
Courtesy of Mark Sensen, FOTW
In a time
when both America and the science of Geology were new, a bright star of invention
shone ever so brightly. He brought with him from his studies at the University of
bases of European geology, as set forth by Hutton, Lyell, and others.
He was born
three years after George Washington and the Continental Congress signed the
Declaration of Independence, and was an elderly supporter of Abraham Lincoln. He
after the fathers of modern geology, James Hutton and Charles Lyell, and was contemporary
(and father-in-law) to James Dwight Dana. In his 85 years, this noted professor laid
foundation for American education in Geology, and our national advancement in science.
author would call him the Father of American Geology Education.
|| Dana, who built somewhat upon the work of his
father-in-law, Benjamin Silliman, has his revised and updated work still used today in
21st century college classrooms. I still refer to my 19th edition from 1977, which
was assigned by my Geology Professor, Dr. Peter Leavens (like
Professor Silliman, a Yale Graduate) at the University of Delaware.
are two modern editions of Dana's Manual of Mineralogy. One book includes a
His legacy lives on in the expansive scientific achievement of
his son Benjamin, Jr. and son-in-law J. D. Dana, also in his extensive collection of North
American rocks, minerals, and fossils in Yales Peabody Museum,
founded just two years after his death. There were only 35 stars on our flag when
our illustrious professor finished his earthly work.
Silliman" Peabody Museum of Natural History, Yale University)
Emeritus Sillimans name is remembered in honor at Yales Silliman College, Mt.
Silliman and Silliman Lake in Sequoia National Park,
by the State of Delaware, and as our favored mineral this month: Sillimanite.
mineral name was grandfathered in 1959 by the International Mineralogical Association
(Source: "Sillimanite" at mindat.org)
(Top): 35-star U. S. Flag, 1863-65, Rick Wyatt, FOTW
(Bottom): 50-star U. S. Flag,
1959-, Joe McMillan, FOTW
Emeritus Sillimans name is remembered in honor at Yales Silliman College,
Mt. Silliman and Silliman Lake in Sequoia National Park,
and our favored mineral this month:
His mineral name was grandfathered in 1959 by the International
(Source: "Benjamin Silliman" at
Silliman" and "The
Collections: Mineralogy" Peabody Museum of Natural
History, Yale University)
Though Sequoia National Park is our nations second oldest park, it touts residence
of four of the five worlds largest sequoias. From scenic meadows one can view
high ridges, resolving ones view up to Mount Silliman (11,000+). In
fact, the first national park (Yellowstone) wasnt named until 1872, seven years
after his death, so; he preceded a landmark American first.
(Source: "Sequoia & Kings
Canyon National Park: What's in Each Area, Fall"
, U. S. National Park Service
View of Mt. Silliman
Courtesy of Mike
In 1805, at age
26, Chemistry Professor Benjamin Silliman was dispatched by Yale
University on a mission to the University of Edinburgh. His objectives were twofold:
procure laboratory equipment, and two, to experience the large-scale lecture methods first
developed by Professor Thomas Charles Hope. Silliman succeeded on both counts with
personal direction of Hope. In order, Hopes firsts in lecture methods
translated into American
firsts at Yale. (Source: "Thomas Charles
Hope, MD, FRSE, FRS (1766-1844)" by W. P. Doyle,
University of Edinburgh website
Therefore, it is
appropriate that The First State, Delaware adopted his namesake as its
official state mineral. Delaware was the first state to ratify the Constitution.
Sillimans time, a new nation needed an identity. With new traditions still
Americans seemed to want a deeper anchor in the New World. Geology gave it one.
discoveries, such as those recounted from the 1804-06 Lewis and Clark
expedition, ancient histories could be devised, thus allowing old ground to act as the
into which a common identity could be instantly fastened.
Writers, such as
Fisher, Novak, and Bedell all agree that geology grounded the American
psyche, both literally and figuratively.
To that which
lied beneath the soil and majestically above, both science and art co-developed,
in overlapping, fashion a means to communicate grandly scaled panoramas in printed and
media to fuel the emerging American imagination. These mega-views inspired the
awareness as could culminate in an image of a cultural grandeur
over that of an older and esteemed
European worldview. One could read a plethora of
fresh books and news accounts on the subject,
as well as view large mural canvases by famous landscape artists of the times.
publications were as enthusiastically received as those of Dana, Hitchcock, and
Lyell, as well as other pre-eminent scientists of his day. In fact, those of his and
members have been revised, and are still referred to today in college classrooms.
Geological Revolution in American Time", Thomas M. Allen, University of Richmond)
Under our topsoil, and eroded on creek
banks, the average observer can spot surface
Sillimanite. Almost as common as quartz in one New Castle County, Delaware location,
this Nesosilicate offers us a glimpse into our local earth's past and present.
Formed in the
Delaware Piedmont, Sillimanite is a common occurrence in north-western
New Castle County. Found in some streams, rounded stones exhibit a brown weathered
like that of a potato skin.
One could find
large boulders just feet from our clubhouse at Greenbank
Mill, Prices Corner.
Geological Survey Open File Report #38 from June 1995, a core sample (#24895) from
45 down on Centerville Road, near Prices Corner, contains Bundles of
sillimanite needles, blades, and large prisms clustered with biotite. (The
Wilmington Complex contains other minerals, some of which may become future MOTM this
(Source: "DGS Field
Report No. 38, 1995", DGS website)
|Delaware Geological Survey
Photo by Ken Casey
geologists of the DGS and USGS, the Wilmington Complex is
extremely ancient. In an
article called "America's
Volcanic Past: Delaware", rocks of the Delaware Piedmont age from
about one-half billion to 1.2 billion years old. Sillimanite is included in the
underlying strata as
component of the Delaware Gneiss.
|Creekbed area strewn with
Sillimanite at BSP
||Closeup of Sillimanite boulder
|Photos by Ken Casey
Sillimanite was formed in a high-temperature metamorphic environment above
550 degrees Celsius over a prolonged time, thus producing coarse grains.
(Source: "Delaware State
Mineral, Sillimanite", William S. Schenck, DGS website
Springs sillimanite is 30% fibrolite by volume. It is an index mineral in this
type of metamorphism.
Investigation of Lewiston, Idaho, fibrolite: Microstructure and grain boundary
energetics", Lee, Banfield, Kerrick, American Mineralogist website)
|BSP Sample #1: Fibrolitic
||BSP Sample #2: Fibrolitic
|Samples courtesy of
Fran Poniecki, Photos by Ken Casey
broken, many specimens reveal parallel fiberlike crystals, resembling a wood-grain
texture. Pertinent colors include white, gray, tan, and green.
On a microscopic
level, the crystallography of Sillimanite as Al2SiO5 can be viewed
both thin-section under the microscope, and as theoretical drawings of their dynamic
Sillimanite consists of chains of aluminum octahedra linked by alternating aluminum and
silica tetrahedra. Goodness knows, before 21st century computer modelings, some of
20th century geology students struggled with self-made cardboard and glue cut-outs of
polyhedra--assembling them to visualize Sillimanite's structure. My first attempt
1977, when coincidentally, the DMS was rallying to propose the naming of an official state
|| Nature favors
the formation of Sillimanite over Kyanite or Andalusite, when temperatures and pressures
together are the highest.
Graphic by Ken Casey
boulders of Sillimanite at BSP
Photo by Ken Casey
Home to George Washingtons Council Oak and the historical site of Camp DuPont and
Brandywine Springs Park, this location also contains stream deposits of
Sillimanite. Though not for the taking, one can observe the geology that hosts these
(Left): Postcard of Brandywine
Springs Park circa 1910
author was fortunate to receive a guided tour of the park by Lonzi, one of the
Friends of Brandywine Springs Park. He showed
me the spring head (which still flows today),
the ancient council oak tree (still on site), and the remnant foundations of the late 19th
early 20th century amusement park (1886-1924). Along with the monthly archaeological
activities that are conducted on site, Lonzi pointed out to me the challenges of
erosion, the maintenance of hiking trails, and importance of safety concerns, such as not
climbing down the stream banks.
||State of Delaware
Historical Marker N.C. 79:
by Ken Casey
Interestingly enough, Rear Admiral Samuel F. DuPont's encampment at Brandywine Springs,
from May 1861 to October 1862, coincided almost with the time that Professor Silliman
President Lincoln. This park contains a large deposit of Sillimanite!
Lonzi, as a park
steward, was also familiar with some of the geology of his park. He showed
me examples of garnets, quartzes, and best of all, Sillimanite. In the interest of
this article, he
showed me the stream deposits of Sillimanite. He would like me to let you know that
is prohibited here, so please enjoy the park space responsibly.
|Bridge over creek at BSP
||Creek boulders, some are
|Photos by Ken Casey
been visiting this park for about 30 years now. Sadly, it is no longer an amusement
park. It has remained naturally unchanged, yet with improved facilities, and does
meet the fun
and recreation needs of its many visitors. I like how it is setup as a clean,
family park. Please do visit, if you are in the New Castle County,
the first county of the First State.
Attractions adjacent to Brandywine Springs Park:
Historic Greenbank Mill (our
The Wilmington & Western Railroad
One can find
Sillimanite prominently displayed in the collections of two important museums of
note: The Yale Peabody Museum and The Irénée DuPont Mineral
Museum at the University of
|Sillimanite Boulder at the U.
Photo courtesy of William S.
||DMS fieldtrip/meeting at the
Irénée DuPont Mineral Museum in 2006 (Ken Casey)
collection contains 46 specimens from the east coast of the U. S. and from around the
globe. A comprehensive list is below:
||Sillimanite can be found in
Connecticut, near Yale at Guilford, New Haven County. Also, at:
Norwich, New London County, Connecticut
||Willimantic, Windham County, Connecticut
||North Woodstock, Windham County, Connecticut
||Winsted, Litchfield County, Connecticut
||Haddam, Middlesex County, Connecticut
||Westbrook, Middlesex County, Connecticut
||Orange, Franklin County, Massachusetts
||Winchester, Middlesex County, Massachusetts
||Wales, Hampden County, Massachusetts
||Monroe, Orange County, New York
||Media, Delaware County, Pennsylvania
||Seneca, Oconee County, South Carolina
||Burke County, North Carolina
||Brandywine Springs, New Castle
||Norway, France, Madagascar, Kenya, Germany,
Czechoslovakia, and Australia
||(Source: Yale Peabody Museum
Catalog Service, Query: Sillimanite)
The major uses for Sillimanite are industrial and aesthetical. By using our car,
park,or by wearing jewelry, we can appreciate this aluminum silicate wonder.
Engine spark plug
manufacture requires the addition of an insulating compound. Pulverized
Sillimanite is employed here.
boulder at BSP (Ken Casey)
(Bottom): Newly manufactured spark plug (Pointshop.com)
Plug Novelty item
(Photo by Terry Schwartz)
As mentioned above, Sillimanite boulders can act as a natural backdrop to outdoor
Perhaps one of you might paint a picture or photograph the park for either geologic study,
art's sake. Happy trails!
The second aesthetic use of Sillimanite is as a gemstone--there's more below.
"Sillimanite is suitable for lapidary work and under the name Fibrolite..."
Geology: State Mineral: Sillimanite", State of Delaware website)
It is the fibrolite components
that contributes towards the optical dispersion noted in cabochon gems cats-eye
effect. The coarser grained material is more suitable to faceted gemstones.
Photo courtesy of Roger
Weller, Cochise College
On the jewelry-side, faceted
fine gemstone material can yield some of the most beautiful
brown-green-yellow color combinations. I understood this use better by enjoying a
club meeting program on faceting,
presented by our own Tom Pankratz. One of Tom's hobbyist
goals is to facet at least one of every major gemstone known to man.
Another DMS member, Bob Todd, is an avid collector of the Al2SiO5
trimorph. Bob specializes
in Sillimanite-Kyanite-Andalusite. He purchases gem rough and cut stones. I
suggested to Bob
at one meeting, that he might consider faceting a very large gem, and call it "The
Star of Delaware".
Who knows what we might see from Bob and Tom in the future.
The 1970s heralded celebration of our nation's bicenntennial. In 1977, our
Delaware Mineralogical Society, proposed an official State recognition of a mineral: our
Before 1830, during Sillimans tenure
at Yale, Delaware geologists found remarkably pure
boulders of Sillimanite in the alluvium of Brandywine Springs.
Geology: State Mineral: Sillimanite", State of Delaware website)
Dana listed this locale in his 6th edition Danas
System of Mineralogy (1892).
events, along with a late 20th-century appreciation of this mineral, culminated in the
celebration, which we observe today.
State Mineral: Sillimanite", William S. Schenck, DGS website)
Delaware sillimanites gem properties kept it in the
public eye for decades, as hobbyists The Act was passed and written into
law as our
lapped and faceted it into chatoyant cabochons and sparkling gems. This attention,
its impressive history, prompted our club to propose to the Delaware General Assembly in
that it be named as the official state mineral.
Delaware Code Title
29 § 310. We celebrate this anniversary on March 24th. So, mark your
calendar, and wherever you are,
please toast with us. Cheers!
CHAPTER 3. STATE SEAL, SONG AND SYMBOLS
§ 310. State mineral.
The official state mineral is sillimanite.
(61 Del. Laws, c. 21, § 1.)
||(Source: "Title 29 §
310", State of Delaware Official website)
Irénée DuPont Mineral
Museum, University of Delaware
Museum of Natural History, Yale University
Brandywine Springs Park, New Castle County, Delaware
State of Delaware Division of Historical
& Cultural Affairs
Historical Society of
DelDOT Projects: Archaeological
Exploration and Historical Preservation in Delaware
Here is where DMS
Members can add their nice Sillimanite photos to share with us.
||(Top, Left): DMS
Junior Chairperson, Fran Poniecki, shows some Girl Scouts samples of Sillimanite at our
October 2006 Educational Event at Greenbank Mill
(Top, Right): Labeled Sillimanite from the Red Clay Creek area
(Bottom, Left): Tray of Sillimanite sample
which Fran shared with the Scouts
(Photos by Ken Casey)
Until Next Time
We hope you have enjoyed our quaint visit to
Sillimanite. Please join
us next month, for another article, and we shall journey together!
Until then, stay safe, and happy collecting.
Fran Poniecki, Junior Chairperson, The Delaware Mineralogical
I would like to gratefully acknowledge the generous contributions of our fellow
collectors, authors, curators, professionals, and club members who made this
work possible. Thanks.
©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
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
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,
graphics. Use of all other credited materials requires permission of each
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
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.
Life of Benjamin
Silliman, M D., LL., D., Late Professor of Chemistry, Mineralogy, and Geology in Yale
College. Chiefly from His Manuscript Reminiscences, Diaries, and Correspondence.: Vol. 2,
Michigan Historical Reprint Series
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: email@example.com.