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                           Mineral of the Month--April 2008

                              Delaware Biotite Mica

                                                             K(Mg, Fe)3AlSi3O10(F, OH)2

                                                 

 



                                        "Delaware Biotite Mica"

                                              By Ken Casey

Preface
Introduction
Why Delaware Biotite?
What's in a name?
Chemistry & Science
Some Biotite Geology
Two Museums of Note
Uses
Links
Members' Gallery
Article Contributors
Photo & Graphics Credits
Suggested Reading
Invitation to Members
Past Minerals of the Month

Delaware State Flag

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

 
 

Biotite Mica crystallizes before...

 

...Muscovite in Bowen's Reaction Series!

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

(Top, right):
Photo by Ken Casey ©2008

Preface    

    

     Greetings, Delaware mineral enthusiasts!  This month, our Mineral-of-the-Month takes around
the First State to find biotites. 

     Spring is here, but bring a warm jacket.  The weather promises to be bright and
sunny today, so
Let's go!

 

Introduction

     

    In part

     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!

In December 2007, we looked at Delaware Muscovite Mica. This month we’ll visit Delaware Biotite Mica. It is a phyllosilicate with almost perfect basal cleavage, and is found in a variety of igneous and metamorphic rocks in The First State.

It was named after French physicist Jean-Baptiste Biot, who in 1816, studied it’s unique properties. Today, the IMA has reclassified Biotite as a group of micas, which contain phlogopite, siderophyllite, and eastonite. These iron micas may be found in and around Delaware. Eastonite, can be located at the C. K. Williams Quarry in Easton, Pennsylvania.

Biotites can be found at the old Wooddale Quarry and Woodlawn Quarry in New Castle County.

With a hardness of 2.5-3, and a dark gray to black coloring, it is relatively easy to identify it in the field. Biotites form at different conditions than Muscovite in Bowen’s Reaction Series. It forms at a higher temperature and with a more mafic composition than Muscovite. Therefore, Biotites crystallize before Muscovite as magma cools.

So come on along, we have another Delaware Mica fieldtrip to make!

"Biotite Gneiss

Mineralogically, the biotite gneisses are composed of plagioclase, quartz, biotite, and iron oxides.  Garnet, sillimanite, and orthoclase in various combinations are also present in the samples.  Accessory minerals are zircon, sphene, and apatite.  Some of the plagioclase grains are antiperthitic.

Megascopically there are two varieites of biotite gneiss, (1) a coarse-grained variety with flaser texture in which biotite defines a strong foliation, and (2) a fine-grained variety, a granofels, with small shredded grains of biotite in random arrangement.  The coarse-grained variety usually contains garnet, sillimanite, and orthoclase; however, these minerals may also be present in small amounts in the fine-grained lithology.  Contacts between the coarse and fine-grained phases are always sharp and may have elongated poikiloblastic garnets concentrated among them."

Harmony Road, Wilmington Complex, Biotite-bearing felsic gneiss

http://www.dgs.udel.edu/publications/pubs/OpenFileReports/ofr38e.pdf

 

Why Delaware Biotite Mica?

 

      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?   

 

     Quartz

Biotite was named by J.F.L. Hausmann in 1847 in honour of the French physicist Jean-Baptiste Biot, who, in 1816, researched the optical properties of mica, discovering many unique properties.

http://en.wikipedia.org/wiki/Biotite

 

 

  (Source: http://en.wikipedia.org/wiki/Quartz)

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

     Much of

 

    Greek

  (Source: http://www.jewelrysupplier.com/2_garnet/garnet_mythology.htm

     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.

 

Biotite-Phlogopite Series

-
KMg
 
3
[(OH,F)
 
2
|AlSi
 
3
O
 
10
]

Biotite - K(Mg,Fe)3(Al,Fe)Si3O10(OH,F)2
Phlogopite - KMg3(AlSi3O10)(F,OH)2

annite (biotite series) KFe3(Si3Al)O10(OH)2
phlogopite (biotite series) KMg3(Si3Al)O10(OH)2

Both Biotite and Phlogopite are mentioned in the DGS's Catalog of Delaware Minerals

 

"

Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula K(Mg, Fe)3AlSi3O10(F, OH)2. More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers include siderophyllite.

Biotite is a sheet silicate. Iron, magnesium, aluminium, silicon, oxygen, and hydrogen form sheets that are weakly bond together by potassium ions. It is sometimes called "iron mica" because it is more iron-rich than phlogopite. It is also sometimes called "black mica" as opposed to "white mica" (muscovite) -- both form in some rocks, in some instances side-by-side.

Like other mica minerals, biotite has a highly perfect basal cleavage, and consists of flexible sheets, or lamellae, which easily flake off. It has a monoclinic crystal system, with tabular to prismatic crystals with an obvious pinacoid termination. It has four prism faces and two pinacoid faces to form a pseudohexagonal crystal. Although not easily seen because of the cleavage and sheets, fracture is uneven. It has a hardness of 2.5 - 3, a specific gravity of 2.7 - 3.1, and an average density of 3.09 g/cm³. It appears greenish to brown or black, and even yellow when weathered. It can be transparent to opaque, has a vitreous to pearly lustre, and a grey-white streak. In its weathered yellow, sparkly form, it is a common type of “fool’s Gold” (Pyrite is the official “fool’s Gold”). When biotite is found in large chunks, they are called “books” because it resembles a book with pages of many sheets.

Biotite is found in a wide variety of igneous rocks and metamorphic rocks. For instance, biotite occurs in the lava of Mount Vesuvius and at Monzoni. It is an essential phenocryst in some varieties of lamprophyre. Biotite is occasionally found in large sheets, especially in pegmatite veins, as in New England, Virginia and North Carolina. Other notable occurrences include Bancroft and Sudbury, Ontario. It is an essential constituent of many metamorphic schists, and it forms in suitable compositions over a wide range of pressure and temperature.

It is not industrially useful, but it is mined using quarrying and underground mining (depending on the depth of the biotite) for collection purposes.

http://en.wikipedia.org/wiki/Biotite

Phlogopite is often found in association with ultramafic intrusions as a secondary alteration phase within metasomatic margins of large ultramafic to mafic layered intrusions. In some cases the phlogopite is considered to be produced by autogenic alteration during cooling. In other instances, metasomatism has resulted in phlogopite formation within large volumes, as in the ultramafic massif at Finero, Italy, within the Ivrea zone. Trace phlogopite, again considered the result of metasomatism, is common within coarse-grained peridotite xenoliths carried up by kimberlite, and so phlogopite appears to be a common trace mineral in the uppermost part of the Earth's mantle. Phlogopite is encountered as a primary igneous phenocryst within lamproites and lamprophyres, the result of highly fluid-rich melt compositions within the deep mantle."

http://en.wikipedia.org/wiki/Phlogopite

 

 

 

Where found?

DELAWARE. Pegmatites?

 

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

   

  Though

  (Source: http://www.uwgb.edu/dutchs/EarthSC102Notes/102ROCKS.HTM

     In the photos below,

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

     Delaware has

  (Source:) 

         What .

(Source: )

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

     For example,

     Our Piedmont

     Therefore,

           

 

Some Delaware Biotite Geology

There is biotite in most all of the gneises of Delaware's Piedmont.    

"This area is comprised on mafic and felsic gneisses and amphibolites of the Wilmington Complex and the metasedimentary gneisses in the Wissahickon, Cockeysville, and Setters formations as well as the migmatitic gneisses and amphibolites of the Baltimore gneiss."

(Taken from “Minerals of Delaware” by Peter B. Leavens, in 1979, Transactions of the Delaware Academy of Science, 1976, Delaware Academy of Science, Newark, Delaware)

http://www.dgs.udel.edu/Geology/Mineralogy/index.aspx

Piedmont Unit, Silurian

Arden
Plutonic
Supersuite
(Saps)

Ardentown Granitic Suite (Sags)
Perkins Run Gabbroic Suite (Spgs)
biotite tonalite (Sbt)

 

Three lithologies have been identified

within the Baltimore Gneiss in the Mill Creek Nappe:

granitic gneiss, hornblende-biotite gneiss, and amphibolite

with or without pyroxene. 

Lack of exposure prevents these

lithologies from being mapped separately. Granitic gneisses

with swirling leucosomes and irregular, biotite-rich, restite

layers constitute approximately 75 to 80 percent of the

exposed rocks. Pegmatites are commonly associated with

the granitic gneisses and are exposed in a series of abandoned

quarries along the northwestern boundary of the

H o c k e s s i n - Yorklyn anticline (Wo o d r u ff and Plank, 1995).

P e t ro g r a p h y. The granitic gneiss is composed of

quartz, plagioclase, biotite, and microcline. Minor and

accessory minerals are garnet, muscovite, magnetite,

ilmenite, sphene, apatite, and zircon (Wo o d r u ff and Plank,

1995). The plagioclase is chiefly oligoclase with myrmekite

concentrated along grain boundaries. Much of the granitic

gneiss is migmatitic.

The hornblende gneiss contains plagioclase, quartz,

hornblende, and biotite with/without orthopyroxene.

Accessory minerals are garnet, muscovite, clinozoisite,

perthitic orthoclase, iron-titanium oxides, sphene, and

apatite. Hornblende grains are pleochroic in shades of

brown-green and green.

The amphibolites are composed of subequal amounts

of hornblende and plagioclase with minor quartz, biotite,

clinopyroxene, and orthopyroxene (Wo o d r u ff and Plank,

------

P e t ro g r a p h y. The Setters Formation and the

Wissahickon Formation are difficult to differentiate macroscopically,

but they can easily be distinguished in thin sections

by identifying feldspars. Microcline with cross hatch

twinning and perthitic lamellae is the most abundant

feldspar in both pelitic and psammitic facies of the Setters

Formation. This distinguishes the Setters Formation from

the Wissahickon in which plagioclase is the most abundant

feldspar and untwined orthoclase is present in small

amounts. Other minerals in the pelitic and psammitic rocks

of the Setters Formation are garnet, muscovite, sillimanite,

quartz, and biotite with minor plagioclase. Accessory minerals

are iron-titanium oxides, zircon, sphene, and apatite.

Myrmekites of quartz and feldspar cluster along grain

boundaries of microcline. Heteroblastic grains of quartz are

commonly recrystallized to smaller subgrains. The plagioclase

shows extensive alteration to green clay, and biotite

may show alteration to chlorite. Sillimanite occurs as fibrolite,

acicular grains, and large prisms that lie across the foliation.

Modal analyses are published in Kuhlman (1975),

Woodruff and Plank (1995), and Plank and Schenck (1997).

Plank and Schenck (1997) compare the Setters in Delaware

and Pennsylvania with the Setters in Maryland.

ironrich

biotite is unstable and breaks down to form garnet suggesting

a reaction such as:

biotite + sillimanite + quartz = garnet + orthoclase +

water (Tracy 1978) or the incongruent melting of biotite:

biotite + sillimanite + quartz + Na-plagioclase = garnet

+ Ca-plagioclase + melt (Calem, 1987; Alcock, 1989).

Mineral assemblages of biotite,

microcline, quartz, and plagioclase indicate the rocks were

metamorphosed to the amphibolite facies.

The biotite tonalite occurs as rounded boulders

with light gray to buff colors on fresh and weathered surfaces.

The tonalite is leucocratic and contains 15-25 percent

mafic minerals. The biotite tonalite can be distinguished from

the Ardentown Granitic Suite in hand specimen by a finergrained

equigranular texture and the scarcity or absence of Kf

e l d s p a r. Chemically, the biotite tonalite differs markedly

from Ardentown Suite rocks of comparable silica content (70

percent SiO2 by weight) in having significantly lower K2O

(0.69 vs. about 3.5 weight percent), as well as some diff e rences

in trace element abundances (Srogi, 1988).

CONCLUSIONS

In this report we have formally named eleven new rock

units, informally recognized two rock units, and redefined previously

mapped rock units in the Delaware and southeastern

Pennsylvania Piedmont. We have redefined the Wi l m i n g t o n

Complex to include all rocks associated with the development

of a Paleozoic magmatic arc; five metaplutonic lithodemes recognized

and herein named the Brandywine Blue Gneiss,

Montchanin Metagabbro, Mill Creek Metagabbro, Barley Mill

Gneiss, and the Christianstead Gneiss; three metavolcanic

units, the Windy Hills Gneiss, Faulkland Gneiss, and the

Rockford Park Gneiss; three igneous plutons, the redefined

Arden Plutonic Supersuite (comprising the Ardentown Granitic

Suite, Perkins Run Gabbronorite Suite, and one lithodeme of

biotite tonalite), the Bringhurst Gabbro, and Iron Hill Gabbro.

The systematic changes that reflect increasing intensity

of metamorphism can be observed in the field as pelitic

assemblages record the breakdown of muscovite to sillimanite

and orthoclase, the breakdown of biotite and sillimanite

to garnet, and the incongruent melting of biotite to garnet

and cordierite. Mafic assemblages in the Wi l m i n g t o n

Complex record the change from blue-green amphibole to

brown amphibole to pyroxene. Precise estimates of peak

temperatures are more difficult because the reaction temperatures

are a function of water pressure, which is unknown

and probably variable, and a higher pressure metamorphic

overprinting is present in the Wissahickon east of the

Wilmington Complex (Crawford and Mark, 1982;

Bosbyshell, et al., 1999). Attempts to estimate peak metamorphic

temperatures and pressures based on mineral

assemblages in garnet-bearing biotite gneisses using petrogenetic

grids and various geothermometers and geobarometers

find:

(1) Brandywine Blue

http://www.dgs.udel.edu/publications/pubs/reportofinvestigations/ri59.pdf

The layering in the Wissahickon wall rock is irregular and defined by stringers of garnet, biotite and sillimanite in a mass of quartz and feldspar. The garnets are dark red, either oval or round, and may be as large as three quarters of an inch in diameter.

 

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.

http://www.dgs.udel.edu/geology/geoadventures/bluerocks.aspx

Mineralogically the Wis sahickon formation is characterized by a composition

indicating extreme metamorphism. The essential minerals present

are quartz, orthoclase feldspar, oligoclase feldspar, biotite, sillimanite

and garnet.

 

Piedmont pegmatite bodies between Newark and Yorklyn..."

The minerals present in the pegmatite dikes are quartz, the potash

feldspar microcline, muscovite, biotite and iron-bearing tourmaline. Of

these, quartz and microcline are most abundant, making up over 75 per

cent of the local bodies."

 

Common detrital minerals in the sands of the Coastal Plain are quartz,

chert, feldspar and rnus covite , Other detrital material occurring in small

quantities (genera.lly 3 per cent or less by weight) is formed by a group of

so-called heavy minerals (s.g. 2.87 or more), suchas the opaque minerals

magnetite, ilmenite, and pyrite, and a great variety of nonopaque grains,

such as zircon, tourmaline, garnet, rutile and other titaniferous minerals,

staurolite, kyanite, sillimanite, andalusite, chloritoid, epidote, hornblendes,

augite and diopside. Some minerals, particularly muscovite and

biotite, have a specific gravity close to 2. 87 and may be found both in the

light and heavy fractions of a sediment. The accessory heavy minerals are

of no great importance insofar as most uses of sand are concerned, except

where very low iron content is desired.

The fine grained clays are generally composed of a group of clay minerals,

which consist largely of hydrous aluminum silicates. Kaolinite,

illite, chlorite and montmorillonite are found in the Coastal Plain deposits.

 

http://www.dgs.udel.edu/publications/pubs/bulletins/bulletin7e.pdf

The Baltimore gneiss is a "quartztzo-feldspathic gneiss, biotite gneiss, biotite hornblende gneiss, and amphibolites".

"Highly metamorphosed biotite gneisses of the Wissahickon are often impossible to distinguish from the biotite gneisses of the Baltimore Gneiss.  Features that characterized the Baltimore Gneiss are (1) intense migmatization, (2) highly variable strikes of foliation, (3) general absence of sillimanite and primary muscovite , and (4) relic granuliate facies assemblages containing orthopyroxene."

The Wissahickon in Delaware contains some metasedimentary pelitic gneisses with biotite, quartz, plagioclase (oligoclase to andesine), and various iron-titanium oxides.

http://www.dgs.udel.edu/publications/pubs/bulletins/bulletin19e.pdf

"...the redefined Arden Plutonic Supersuite

comprising the Ardentown Granitic Suite,

Perkins Run Gabbronorite Suite, and one

lithodeme of biotite tonalite; and three

metavolcanic units named the Rockford Park

Gneiss, Windy Hills Gneiss, and Faulkland

Gneiss."

http://www.dgs.udel.edu/publications/pubs/fsg/v19no1.pdf

"A mineral with perfect basal cleavage that easily separates into

sheets. The varieties are black biotite, white muscovite, bronze

phlogopite, and green chlorite. Micas are common in all Piedmont

rocks except the high-grade gneisses of the Wilmington Complex."

 

Baltimore Gneiss—represents the ancient North

American continent; rocks are interlayered granitic gneiss,

biotite gneiss, pegmatite, and amphibolite.

 

 

In Delaware, the Baltimore Gneiss is a contorted mixture of

granitic gneisses, biotite gneisses, amphibolites, and pegmatites.

 

Wissahickon rocks always show two types of layering that

are parallel to each other: (1) a gross layering between the

rock units (e. g., between the gneisses and amphibolites) and

(2) a fine light-dark compositional layering within each rock

unit (Figure 25 A and B). The gross layering is presumed to be

parallel to the original sedimentary beds, and the fine compositional

layering

is thought to be

a result of a

process called

metamorphic differentiation.

During metamorphic

differentiation

the light

minerals, quartz

and feldspar,

migrate to form a

light layer, while

the dark minerals,

garnet,

biotite and sillimanite,

form a

dark layer. Thus

the overall composition

of the

rock remains the

same, but the

individual bands

have strongly

contrasting compositions

that

are completely

different from

the original rock.

 

Figure 25. Layering in the Wissahickon

Formation:

(A) Gross layering between black amphibolite

and light-colored gneiss.

(B) Fine compositional layering in the

gneiss, Wooddale Quarry; note the cross

cutting pegmatite pods.

 

http://www.dgs.udel.edu/publications/pubs/specialpublications/sp20.pdf

 

 

Biotite is used extensively to constrain ages of rocks, by either potassium-argon dating or argon-argon dating. Because argon escapes readily from the biotite crystal structure at high temperatures, these methods may provide only minimum ages for many rocks. Biotite is also useful in assessing temperature histories of metamorphic rocks, because the partitioning of iron and magnesium between biotite and garnet is sensitive to temperature.

Biotite is used in electrical devices, usually as a dielectric in capacitors and thermionic valves.

http://en.wikipedia.org/wiki/Biotite

Moving down this series you move from minerals that are least resistant to weathering, or most easily broken down, to minerals that are most resistant to weathering, or the hardest to break down. A few things to note regarding this sequence: First, this sequence includes only primary silicates.

Second, looking at the minerals, the most resistant minerals are felsic while the least resistant minerals are mafic. In a weathering environment like that in the southeast region of the U.S. you essentially will not find mafic minerals in soil - they will all have weathered away to secondary minerals. Quartz and muscovite are more common in soils than any of the other primary silicates.

http://www.soils1.cses.vt.edu/MJE/intro_soils/mineral_rocks_weathering_v/Bowens.shtml

 

     
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, wikipedia.org

 

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

  (Source:  http://www.udel.edu/dgs/Publications/pubsonline/SP20.pdf
)

 

   

     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

 
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
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

 
     
 

    The fabri

  (Source: http://www.udel.edu/dgs/Publications/pubsonline/report38/31.html

 

 

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

     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    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.”

  (Source:  http://www.udel.edu/dgs/Education/bluerocks.html

     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!

 
 
 

    

     If

    

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

 

Uses

     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)
 
 

Links

 

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

 

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

 

wikipedia.org

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. 
Thanks.

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

Marchex, Inc., World Flag Database

wikipedia.org

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: kencasey98@yahoo.com.


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?

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: kencasey98@yahoo.com, 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: kencasey@delminsociety.net

This page last updated:  February 19, 2011 10:15:18 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
(Monday)

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
 

Fieldtrips!

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

Updates!

 

 

 
Articles

 

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?

Past MOTM

Collecting Adventure Stories:

"Sunny Brook Crick Goethite" by Joe Dunleavy