Roadcuts are great places for Pa. rockhounds to find fossils and minerals

Although roadcuts can be dangerous locations to seek rocks, minerals and fossils, several roadcuts in York County have produced several noteworthy nice and unique mineral specimens.  Be respectful of property owners, as not all roadcuts are rights-of-way owned by the state or local municipalities.

The first roadcut is known as the Rossville Copper location.  The site is located 0.65 mile north of Rossville on the east side of Old York Road in Warrington Township.  Old York Road was expanded and repaved in 1972.  It was during the construction that some colorful pieces of malachite and azurite were collected by local “rockhounds.” 

The copper mineralization was found on a metamorphic rock known as a hornfels.  The rock was originally a shaly rock, but due to a magma intrusion just to the south, altered the rock by heat and formed microscopic blebs of native copper in the hornfels. The magma cooled into diabase about 150 million years ago.  Over time, the native copper was weathered and formed the malachite and azurite on the outside joint surfaces of the rock.  The copper minerals occur in a 14-inch thick bed and is 2.07% copper, not enough to be economically valuable.  Later research at the location showed that opal hyalite, a green fluorescent mineral, does occur on some of the joint edges of the hornfels.

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Another roadcut, in West Manchester Township, was located on the east side of Carlisle Ave. (Route 74) just south of Loucks Road.  Here, within the Cambrian-aged Kinzers Formation shale, Olenellus and Wanneria trilobites and hyolithes fossils were collected in the 1960s into the early 1970s.   For some years, this site was the premiere location for finding some of the oldest marine life in Pennsylvania.  Serious excavations into the hillside and yard of the property owner discontinued the collecting here.  As a side note, during construction of the Holidrome Hotel in 1981, a fossil echinoderm was collected and is considered one of the oldest starfish found in the fossil record.  The specimen is housed today at Harvard University.  

The construction of U.S. Route 30 in York County created quite a stir for rockhounds as several roadcuts were created.  One roadcut that did create an opportunity to collect a rather rare mineral is found on the north side of the road, just east of the Mount Zion Road interchange.  Chamosite, a chlorite group member, was discovered by mineral collector Jay Lininger in 1970.  Jay presented specimens to the Pennsylvania Geologic Survey for analysis.  Chamosite occurs in the Antietam Formation sandstone as small dark green flat aggregates usually associated with quartz.   It has a very bright luster and can be determined by scratching with a fingernail, often leaving a dull, light-green impression.  Chamosite was discovered in 1820 by French mineralogist and mining engineer Pierre Bertier near the town of Chamoson.  Chamosite is regarded as a rather uncommon mineral around the world.

During interchange improvements at the Leader Heights exit of U.S. Interstate 83 in 2008, nice pyrite cubes and limonite pseudomorphs were found on the hillsides.  Here pyrite crystals, some measuring up to 1.5 inches square, resting in the Harpers Formation phyllite, were collected. Some of the pyrite exhibited the classical striations across the gold colored crystals, some of the crystals had begun to weather and are brown in color.  These are known as limonite pseudomorphs where the chemical formula has altered from the pyrite.

An active collecting roadcut is on the north side of Locust Lane just west of U.S. Interstate 83.  Here the Kinzers Formation shale is nicely exposed and is easy to split into thin slabs.  This site was brought to my attention in the early 1990s by a rockhound friend.  He showed me a specimen of a head of an Olenellus trilobite and told me he found it at this Manchester Township locality.  Some years later, I saw a complete trilobite from Locust Lane that was collected by a Red Lion area resident.  I have discovered that trilobites show up better on weathered surfaces.  Go out and split the shale into layers and allow the rock to sit and weather for six months and you will have better luck in adding to your collection.

Jeri Jones writes regularly about regional geology.

Also of interest, a gallery of photos below: