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NJ 'traprock' Page 1
'Traprock' is a quarryman's term for the igneous formations in the
rift basin exposed in northeastern and central New Jersey and
southeastern Pennsylvania. These igneous formations are interbed-
ded with sandstones ('brownstone') and shales that contain fossils
of upper Triassic to lower Jurassic age, around 180 million to 200
million years old. They consist of basalt lava flows exposed in the
Watchung ridges and the diabase sill forming the Palisades. The rift
system in New Jersey and Pennsylvania is part of a series of rifts
exposed along the east coast of North America from Nova Scotia to
North Carolina. Other rift basins lie buried further south. Current
theory is that these rifts were formed during the initial separation of
North America and Africa that resulted in the formation of the
present-day Atlantic Ocean. As the continents pulled apart, the
basins between were filled by sediments shed from those continents.
This rifting was accompanied by igneous activity as upwelling mag-
ma was the driving process that produced the basins. In fact, the
same 'spreading centers' are active today at the Mid-Atlantic Ridge.
The Watchung basalts were apparently erupted into large freshwater
lakes, similar to those of east Africa, as evidenced by the the forma-
tion of 'pillow lavas'. 'Pillow lava' is a structural formation in a lava
flow, consisting of rounded masses of lava ('pillows'), that is char-
acteristic of lava erupted into water. This structure leaves large open-
ings between the 'pillows' which allow large mineral crystals to grow.
Solutions of varying composition circulating through the lava flows
have deposited a large variety of minerals in these cavities. The
specimens on these pages are a small sample of that variety.
M1835
NATROLITE
Upper New Street Quarry,
Paterson, Passaic County, NJ, USA
Unusual group of eroded composite natrolite
crystals.
Specimen size - approx. 11 cm. X 8 cm. X 6.8 cm.
M1869
PREHNITE, CALCITE
Lower New Street Quarry,
Paterson, Passaic County, NJ, USA
White calcite crystals on green prehnite
'fingers'.
Specimen size - approx. 11.5 cm. X 11 cm. X 8 cm.
M1870
APOPHYLIITE
Prospect Park, Passaic County, NJ,
USA
Group of large, white apophyllite crystals on
balls of radiating pectolite.
Specimen size - approx. 10 cm. X 9 cm. X 6.7 cm.
M1834
STILBITE
Houdaille Quarry, Springfield,
Union County, NJ, USA
This locality is usually referred to as 'Summit'
but the quarry is actually located in Springfield.
A ball of pale brown stilbite.
Specimen size - approx. 6.5 cm. X 6 cm. X 6 cm.
M1834
AGATE
UBC Quarry, Great Notch,
Passaic County, NJ, USA
Unusual fortification agate from the New
Jersey traprock.
Specimen size - approx. 6.2 cm. X 5 cm. X 5 cm.
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