Fluorescent Concrete, Franklin, New Jersey

Contributed by: Chris Clemens
Date: Apr 24th, 2026
Locality: Trotter Mine, Franklin Mine, Franklin, Sussex County, New Jersey, USA (See on Mindat)
Size: 3.48 x 1.93 x 5.44 inches
Weight: 638 g

Description:
This specimen is an excellent example of building with the materials at hand. It is a piece of concrete, collected from the Trotter Dump, Franklin, New Jersey. It likely originated as part of the foundation for one of the Franklin Mine buildings and is composed of waste sand and mine tailings containing some of our favorite fluorescent Franklin minerals. Waste material from the Franklin Mine was often used for construction purposes. Looking quite ordinary under visible light, this piece of concrete shows a spectacular multi-colored fluorescent response under short wave UV, dominated by the green of willemite, red/orange of calcite, and blue fluorescing hardystonite. This specimen is literally a piece of Franklin history!

Originally posted by Chris Clemens on Nature's Rainbows in 2016.