T(l-r): Peanut Stone, Sandstone, Iron slag
B(l-r): Gardeners Clay, Quartz
Peanut
Stone: Iron-Cemented
Sandstone and Quartz
Sandstone,
iron, and quartz
are all found in a local sandstone that looks like chunks of peanut
brittle in the wrack line.
“Peanut
stone” is a quartz-studded ironstone
of limonite
formed 11-9 million years ago (slide
3) during the Tertiary
period.
It
is part of the Cohansey
sand formation near the top of the Mount
Pleasant Hills across the bay From Sandy Hook (the Cohansey
sands extends south through the Pine
Barrens and becomes the largest
water-table aquifer in NJ).
The
peanut stone is the caprock
of the ridgeline that has prevented the Mount Pleasant Hills from
washing away to flatlands like most of the Bayshore. At 266 feet,
Mount
Mitchell in Atlantic Highlands is the highest
point south of Maine directly on the coastline. During the last
Ice Age (the Pleistocene Epoch) this ridgeline may have been “...
as high as 600 feet above (ancient) sea level ...”.
Locals
have been using peanut stone since
the 1880's to build chimneys, walls, the
Dempsey house in Leonardo, the Stone
Church in Locust, and the stone
bridge over Grand Avenue in Atlantic Highlands.
Ironstone
used to be mined and smelted in Monmouth County for its iron ore.
“European settlers mined
bog iron in local streams” for its iron ore “to produce
utensils, such as plows and axes, and cannon balls for the American
Revolution.” Ubiquitous and slimy iron
bacteria produce a floc
in streams and seeps in Monmouth that resembles Acid
Mine Drainage, and an iridescent
rainbow sheen that mimics oil spills.
The
first iron works in NJ was constructed around 1674
in Tinton Falls. The industry peaked after
the
war of 1812 until about 1844, when transporting coal and richer ores
of iron from
Pennsylvania
became more cost-effective (Forman, 1998).
Chunks
of iron
slag from iron smelting are scattered like small meteroites
in the bay
and ocean wrack lines at Sandy Hook.
Much
of the other sandstone and clay concretions
washing up on the beach are from Sandy Hook . The surface of Sandy
Hook is very young, only about 3-4000 years old (see Holocene
Deposits), but it rests on sediments that are more than 250
feet deep. They may have began accumulating after the peak of the
last Ice Age 25,000 years ago, when the Atlantic coastline almost
reached the Hudson Canyon, about 100
miles offshore today.
They
are also from submerged barrier beaches that developed from 12,000
to 7,000 years ago when sea level was lower (see Holocene
Deposits). Small shells and other “neofossils"
can often be observed in “chunks
of well cemented beach sand, displaying bioturbation and marine
fossils, [that] are eroding from these submerged barriers”,
that are as near as a
few hundred feet offshore.
The
oddly molded chunks of Gardeners Clay (Figure
148A) that washes up on the ocean beaches after storms has been
found in sediment cores at Sandy Hook near Spermaceti Cove (pps.
29-31) as well as beneath Long
Island. Gardeners Clay is a glauconitic, foraminiferal
marl and sand that was formed
in an ancient bays.
Quartz
The
peanuts in peanut stone are quartz,
which is the most common pebble found on the beach.
Quartz
is the second most abundant mineral on earth (after feldspar),
and is found throughout NJ in igneous
rocks like
granite, sedimentary rocks like sandstone, and metamorphic rocks like
schist and gneiss.
Sand
is made of fragments of rocks
and minerals including quartz. Quartz can be found in all
four provinces in NJ, but originally eroded from the Appalachian
Mountains (p.
142). The Beacon
Hill Gravel that formed
9-7 million years ago at the top of the Mount Pleasant Hills has
been called “essentially
the same” as the “modern gravel deposits on Sandy Hook”.
The
different colors in quartz are caused by the chemicals present while
it is crystallizing from molten magma.
Colors include citrine,
rose quartz, amethyst, smoky quartz, and milky quartz. The
rust-stain common in the quartz pebbles in the wrack line is from the
iron
in the soil or groundwater.
Selected
References
Forman,
Richard (Ed.). 1998. Pine Barrens: Ecosystem and Landscape
The
other four parts of this blog are at http://pehealthnj.blogspot.com/
.
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