Delaware mineralogical society

A Delaware 501(c)(3) non-profit earth-science educational organization

 

Brinton's Quarry, Weston Township, PA

Minerals

 
Field Collecting Trip
Brinton’s Quarry
May 14, 2016
9:00 am


Hi DMS members,

We have been invited by Pa Friends of Mineralogy to join them on a field collecting trip to Brinton’s Quarry on May 14, 2016.

We’ve collected at Brinton’s several times in recent years, but the ‘rules’ have changed a bit for this year. First off, we will not be using any excavation equipment, and second, each of us will be limited to collecting no more than 25 specimens (which is a lot when you think about it).

Brinton’s Quarry is located in nearby Weston Township, Pa. Although it is no longer an active quarry, in its heyday it produced more serpentine building stone than any other quarry in the U.S. Quarrying started in 1720 and continued intermittently under various owners until 1941. In 1900 2 of the 3 pits flooded and since have been used as swimming holes. The site is now The Quarry Swim Club.

Brinton’s quarry has 3 pits. One, known as Brinton’s Old Quarry is now flooded and overgrown and it is impractical to collect. A second pit, known as Ingram’s or Farrell’s Quarry is flooded and is the swim club. The third pit is Brinton’s west quarry and though it is somewhat overgrown, there is plenty of open area to collect. The swim club pit and the west quarry are separated by a granite dike, and it is where the serpentine meets the dike that most of the interesting minerals are found.

Brinton’s quarry is in a lens of serpentinite about 0.65 mi. wide surrounded by the Doe Run Schist of the Glenarm Formation. The serpentine contains veins of magnesite and magnetite and smaller seams of ‘deweylite’, talc, and other alteration products. A dike of white granite several feet wide cuts the serpentine. The dike is composed of quartz, feldspar, and muscovite with accessory schorl. The serpentinite also is cut by irregular pegmatite dikes; some are composed of feldspar and muscovite with little quartz, some of kaolinized feldspar and vermiculite, and others of pure vermiculite.

Brinton’s quarry is the type locality for clinochlore and the jeffersite variety of vermiculite, and both minerals may still be easily found. Other minerals found at this site include actinolite, albite, antigorite, beryl, brucite, chromite, chrysotile, deweylite, enstatite, goethite, hematite, hydromagnesite, ilmenite, kaolinite, limonite, magnesite, magnetite, muscovite, quartz, schorl tourmaline, serpentine v. williamsite, talc and tremolite. This site also has some fantastic, colorful, and ceramic-like slickenside.

If you are interested in joining us on this trip, please contact Tom Pankratz by email or phone: tjpankratz@verizon.net, 302 239 0140. I will confirm your sign-up by email…if I don’t please re-contact me.
Further details and directions will be provided to those interested about a week before the trip.
 
(The previous info was taken, sometimes verbatim, from The Mines and Minerals of Chester Co., by R. Sloto)

Brinton’s Quarry Field Trip Report

April 11, 2014

At the invitation of the Pennsylvania Friends of Mineralogy we visited Brinton’s Quarry again.   We had visited the quarry with them last fall for a ‘machine’ dig where loose rock was turned over and some walls exposed, but pretty much everything was covered with dirt making it hard to find specimens.   So we wanted to go back to see what winter’s rains had uncovered.   About 19 DMS members joined a half-dozen Pa Friends to make it a very-well attended event.

We gathered in the parking lot at 9am and were led by Steve Glazier, our host from The Quarry Swim Club, to the west quarry.   We were lucky to have a nice warm dry day which always makes collecting more fun and productive. 

As expected, the rocks were nicely washed off and it didn’t take long for people to be spread evenly throughout the quarry.   In general I think collecting was more productive than in the fall.  Specimens found include:

Clinochlore:  Clinochlore was readily found by pretty much everyone.  There are 2 types: one that looks black to the eye and one that looks metallic green.  A thin sheet of the ‘black’ clinochlore looks green when held up to the sky.  Possilbly the color differences are due to differing mg/iron ratios.  Brinton’s west quarry is ‘L’ shaped with a shorter wall to the east and a longer wall to the south.  The black clinochlore was primarily found in veins on the east wall with books as big as 1 ½ “ across and 1/8” or so thick.  The green clinochlore is found in the rubble below the south wall, and also on the wall just above a pegmatite (very weathered feldspar and quartz) vein located approximately in the center of the wall.   This clinochlore is well weathered, but with care 1” books can be taken (see sample preparation following this report). There is one report of a blue-toned clinochlore found in the rubble on the east wall.

Vermaculite:  Vermaculite, (v. Jeffersite) was readily found in the south wall rubble and immediately below the pegmatite vein on the wall.  In some places the vermiculite is in the feldspar at the edge of the vein.  The vermiculite is a metallic brownish-bronze and books, taken with great care, were as large as 1 ½” and ¼” thick.

Pegmatite:  The pegmatite vein in the top center of the south wall deserves a few words. Though the ridge that separates the 3 quarries at this site is said to be pegmatite, the vertical vein is the only visible pegmatite in the west quarry.  The vein is readily visible from the quarry floor because it is highly weathered and forms a cleft between the serpentine on either side.  The vein forks as it comes down the wall.  The right-hand (west) fork is the least weathered, though all of the rock here is well weathered and can be easily dug with a hand trowel.  From the top down, the sequence of rocks is

1.     Serpentine

2.    Chlorite schist with areas of bright, metallic green clinochlore

3.    The pink feldspar and grey quartz pegmatite

4.    Vermiculite

5.    Serpentine

Last fall we used the backhoe to try to dig out this vein lower down in the quarry where hopefully it was less weathered, without success.  This steepened the wall considerably and makes it harder to get to the exposed vein.  Perhaps more excavation would eventually have exposed a better part of the vein. 

Magnesite:  Veins of white magnesite cut pretty much everywhere though the serpentine and many specimens were collexcted, including one 100# ‘white’ boulder of magnesite-coated serpentine.

Serpentine:  Most of the loose rock and walls are serpentine.  Most has weathered grey, but a bit of cleaning bring back the green.  Some lizardite, deweylite and talc specimens were reported. 

Slickenslide:  Several specimens of colorful slickenslide were found (see pictures).  In general the slickenslide specimens collected here have a wide range of colors and have a porcelain-like finish.  Of all the rocks found here, the slickenslides are the most striking and, if enough could be found, would make a fabulous display.

Quartz:  Specimens of druzy quartz plates were found in the loose rock beneath the south wall.  Liz Smith found plates near the top of the south wall, slightly to the east of center, which led to the finding of in-place veins near the top of the wall.   Many specimens were collected here.    To the eye the plates are very dark (brown and black) and the quartz crystals not cleanly visible.   However, following cleaning with a power washer and muriatic acid (see following sample preparation section) the quartz crystals appear quite stunning when viewed with a dissecting microscope.  These druzy quartz veins appear to be due to the weathering of the serpentite, and not part of the nearby pegmatite.

Brucite:  One specimen of possible brucite was reported

Actinolite:  One specimen of actinolite was reported.

The following  description of Brintons Quarry was taken, sometimes verbatim, from ‘The Mines and Minerals of Chester Co., by R. Sloto

Brinton’s Quarry is located in nearby Weston Township, Pa.    Although it is no longer an active quarry, in its heyday it produced more serpentine building stone than any other quarry in the U.S.  Quarrying started in 1720 and continued intermittently under various owners until 1941.   In 1900 2 of the 3 pits flooded and since have been used as swimming holes.  The site is now The Quarry Swim Club.

Brinton’s quarry has 3 pits.  One, known as Brinton’s Old Quarry is now flooded and overgrown and it is impractical to collect.   A second pit, known as Ingram’s or Farrell’s Quarry is flooded and is the swim club.   The third pit is Brinton’s west quarry and though it is somewhat overgrown, there is plenty of open area to collect.  The swim club pit and the west quarry are separated by a granite dike, and it is where the serpentine meets the dike that most of the interesting minerals are found.

Brinton’s quarry is in a lens of serpentinite  about 0.65 mi. wide surrounded by the Doe Run Schist of the Glenarm Formation.  The serpentine contains veins of magnesite and magnetite and smaller seams of ‘deweylite’, talc, and other alteration products.   A dike of white granite several feet wide cuts the serpentine.  The dike is composed of quartz, feldspar, and muscovite with accessory schorl.   The serpentinite also is cut by irregular pegmatite dikes; some are composed of feldspar and muscovite with little quartz, some of kaolinized feldspar and vermiculite, and others of pure vermiculite.

Brinton’s quarry is the type locality for clinochlore and the jeffersite variety of vermiculite, and both minerals may still be easily found.  Other minerals found at this site include actinolite, albite, antigorite, beryl, brucite, chromite, chrysotile, deweylite, enstatite, goethite, hematite, hydromagnesite, ilmenite, kaolinite, limonite, magnesite, magnetite, muscovite, quartz, schorl tourmaline, serpentine v. williamsite, talc and tremolite.

 

The following section was written in response to several members requesting information on how to clean an prepare specimens collected at Brintons:

Hi,

I hope everyone had as much fun at Brinton's as I did.....great weather makes such a difference.

A few of you had questions about how to clean and prepare specimens.  Here's what I do:

1.  First off, what you do depends on the specimen you have.   Mica-like clinochlore and vermiculite and specimens and rocks with white magnesite are handled very much different than serpentine or quartz plates, and specimens with the porcelain-like slickenside are handled different still.

2.  Clinochlore and vermiculite specimens

These are very fragile.   Put some warm water in a bucket and gently swish the specimen to wash away the really loose stuff.  Then place the specimen where it can dry.   I put them on my wood-burning stove top.   Let them dry.  Drying alone will toughen them somewhat.  Then I briefly soak the specimen in a solution of ButVar in acetone.   You likely don't have any ButVar.  It can be purchased on-line as a solid and acetone can be purchased at any hardware store.  Make a 5% solution w/v.

ButVar is used regularly by the fossil-preparation people.   Dry your specimen again.   It will have toughened considerably.

Or get some of the non-glossy driveway (mortar/brick) sealer that's available at most hardware stores.   Get the type that dries clear and non-glossy (unless you want to add a bit of gloss/sheen to your specimen).   Dip it briefly, dry, and you'll have a much-tougher specimen.

Some people use spray varnishes.   I don't.

I also use ButVar for a variety of other reasons, for example, making sure an asbestos specimen doesn't shed asbestos.

3.  Magnesite, slickenside and other 'fragile' surfaces:   I hold these in a bucket of water and brush lightly with a fine paint brush.  They usually stand up well to being gently hosed off.

4.   Rocks, quartz and many other tougher crystals including calcite:   You can rinse and brush there, but I invariable end up using my 3000 lbs pressure washer.

I usually start with a 'scrap' specimen to see how it goes.   Start with the nozzle a foot or so away and slowly move closer.   I put the specimen on a well-used plastic door mat to keep it in place, and often have to use the toe of my knee-high rubber boots also (warning:  DO NOT HOLD ROCK IN HAND OR WITH BARE FOOT, the pressure washer will wash the skin right off you, and WEAR GLASSES; stuff can fly in all directions, everywhere).

The club owns a small, very high pressure, washer that's available to all members.   I have it.  Just email me and I'll get it to you somehow like at a meeting.

A pressure washer cleans down into the finest crevices.   A pressure washer will take the weathered surface of a rock off, revealing the usually-prettier interior.

A pressure washer will take magnesite and slickenside right off the sample.

Many samples are discolored due to iron staining.   I use Super Iron Out (again, available at most hardwares).  A small handful in a gallon of room temperature water in a bucket, enough to cover the specimens.   Iron Out reduces the insoluble iron+3 to the more soluble iron+2.   I cover the liquid surface with a sheet of plastic wrap to keep oxygen out.   Most specimens only need an overnight soaking, some a day or two.   Then rinse in water for at least overnight, but I usually wash the samples for a couple of days with at least 2 changes of water.   It takes time for the 'solubilized' iron to diffuse out of the rock.   Sometimes I'll give the sample a second, and rarely a third Iron Out treatment.

It looks like the druzy quartz plates several of us got at Brinton's will require prolonged treatments.  I treated mine overnight and though they are cleaned up considerably, there's a long way to go.   I'll bring excess samples to Monday's meeting for anyone who wants one (as well as stabilized clinochlore and vermiculite).

Both phosphoric acid and muriatic acid are often used to clean specimens.  I usually don't use them, at least not as a first treatment.  Of course, if you want to get rid of calcite, limestone, etc.  you have to use acid.   If you do use these acids, do so outside, wear gloves and safety glasses and have a bag of garden limestone open and next to you to neutralize any spills AND have another bucket with water and garden limestone already in it so you can quickly wash splashes from yourself and clothing.

BE CAREFUL: MIXING ACIDS WITH LIMESTONE CAUSES A LOT OF FROTHING AND SPLATTERING FROM THE RELEASED CARBON DIOXIDE.  As a rule-of-thumb, always add acids to water or limestone......don't add the water or limestone to the acid.....order of addition is important to prevent splattering.  And don't add acids to dry limestone.   First put the limestone is some water, then add the acid.

When done, use your garden limestone to clean up all your 'waste' acid.  Do not pour the acid down the drain.  After the acid is completely neutralized, the water with the excess limestone can be spread about your lawn.

DO NOT USE MASONRY LIME:  IT IS HIGHLY CAUSTIC AND WILL CAUSE SKIN AND EYE BURNS.

That's it for Brinton's stuff.