Rutherford Police Chief John Russo said the jar was reported Wednesday morning at the side of a road outside of Rutherford High School and the Bergen County Bomb Squad was called in to analyze the object and its contents, the South Berganite, Rutherford, reported Thursday.
The bomb squad conducted a "blast and cap" to remove the lid from the jar, which was marked "Warning Do Not Remove Cap," "Do Not Ingest," "Never Add Water or Other Substance," and "Warranty Void if Cap Removed."
The bomb squad tested the glass jar and determined it was a piece of a lava lamp, Russo said.
Investigators were unable to determine how it ended up at the side of the road.
The lava lamp -- whose base is filled with colorful wax in a clear liquid that moves around as it heats up from a light bulb -- was a popular consumer item in the 1960s and '70s.