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Located on the exposed serpentinite hill adjacent to R-278 near the Petrides School (or the former location of the College of Staten Island) in Sunnyside, Staten Island, New York. Attempt access only from Lightner Avenue, off Slosson Avenue.
This is the first of several true geology “geocaches” since they all describe some aspect of the unique geology of Staten Island, the truly “forgotten borough.” This cache is located on Staten Island’s exposed bedrock, called the Staten Island Serpentinite. This rock is approximately 425-450 million years old and belongs to the lower Ordovician Period of the Paleozoic Era. This rock was formed when an island arc system, similar to that of the Aleutian Islands of Alaska, collided with an eastward moving proto-North American continent. The resulting collision or mountain building event known as the Taconic Orogeny, formed the original Appalachian Mountains. During this collision, slivers of the Earth’s upper mantle were injected into the crust and survive today as variously-sized serpentinite blobs. Another similar blob appears under Steven’s Institute in Hoboken, New Jersey. These serpentinites are part of the Appalachian Ultramafic Belt that stretches from Newfoundland to Alabama. On Staten Island, the serpentinite bedrock reaches up to approximately 411-413 feet above sea level, making it the highest point on the Atlantic Coastal Plain which runs from the southern tip of Maine to the Gulf of Mexico. Note that Maine’s Cadillac Mountain in Acadia National Park, Mount Desert Island, is NOT part of this plain.
On the whole, this rock is jet black in color when fresh, but chemical weathering from the atmosphere turns it rapidly from black-to-green-to-yellow-to brown, due to the oxidation of the iron-rich minerals present. Looking more closely at this rock, it contains many unique minerals and some rare types as well. Formed from the hydrothermal (hot-water) alteration of an iron-magnesium rich igneous (fire-formed) mantle rock called a peridotite, the original olivine and pyroxene minerals were transformed. By the application of heat, pressure, and chemically active fluids, or a process known as metamorphism, this peridotite became a serpentinite, now a metamorphic rock.
The new minerals are known in order of abundance as lizardite, chrysotile, and antigorite and are the main members of the Serpentine Group Minerals. The lizardite occurs as apple-green to dull green-white grains or masses, which will stick to your tongue when licked! Chrysotile forms short, soft and flexible white cross-fibers in narrow veins, while the antigorite forms sharp, splintery (painful) and brittle waxy-green or bluish-green fibers in small fault or shear zones. Associated with the minerals are others known as magnetite, chromite, brucite, and talc. The magnetite occurs as small but sharp 8-sided black crystals or octahedrons, which are attracted to a magnet when freed from their host, while the chromite occurs similarly but is not as magnetic. Brucite exists as flat masses of silvery-white but clear sheets or books, while the talc is silvery white and very slippery to the touch. This last mineral occurs as isolated white reflective flakes or in abundance as greenish-white masses in cracks and fractures within the serpentinite. In other parts of the world, talc is used to make talcum powder. Over time, chemical weathering again begins to transform the brucite into some interesting new minerals. Rare golden brown, hexagonal flakes called pyroaurite have been found here along with powdery white coatings or masses of hydromagnesite hemispheres, which react or bubble with the application of dilute hydrochloric acid. Rarer is artinite, which forms snow-white masses of pointed and brittle crystals that radiate from a common central point. Feel free to search and collect some of these minerals!
From the top of this hill, exposed to view when the Staten Island Expressway (R-278) was built to accommodate the traffic from the Verrazano Narrows Bridge (VNB), look to the east to see the massive bridge between Brooklyn and Staten Island. The valley before it is part of Clove Valley and the Clove Lakes Fault. Here an ancient and non-active fault has broken the serpentinite, sometime in the geologic past. Much later geologically speaking, approximately, 10,000 to 15,000 years ago during the Pleistocene Epoch, a large continental-sized glacier came down from Canada when the climate was much colder. The action of glacial movement removed or plucked out the broken serpentine rock and smoothed out the bedrock on both sides and formed the present-day U-shaped valley. If it were not for the fault and glacial activity, engineers would have to bore a long tunnel through the serpentinite to connect R-278 to the bridge!
Park in suggested location only. Terrain is overgrown in summer and has some steep paths to climb in both directions. To get safely to this cache, park close to the end of Lightner Avenue on the right side. This street is located off of Slosson Avenue. Do not explore or take anything from the garden at the end of this street! At the end of the road, look for another short road to nowhere on the right before the garden. Due to the recent construction on R-278, the original trail has been blocked off. There is a massive tiered concrete house on the right. Follow this trail downward to a red & white painted glacial boulder on the trail. It marks where you turn LEFT before the petroleum pipeline marker. From here you have to slightly bushwack until you reach a massive pile of dirt. The construction crews have almost completely covered and filled-in the un-used road that formerly existed here. Now rather than walk up the small hill, simply follow the trail on the top of the outcrop. The cache is in a new clear plastic Tupperware container and the log has been replaced. Please replace the cache as you found it!
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