There’s a glow coming from the depths of this historic zinc mine in New Jersey.

Formerly pale, flat, unlit rocks and minerals turn vibrant orange, pink, and green when the overhead lights are turned out and the black-light turned on. They streak with red or develop otherworldly glowing veins of light that were definitely not visible before.

These are the glowing, fluorescent rocks of the Sterling Hill Mining Museum, and the museum has hundreds of them, making it home to the largest publicly displayed collection of fluorescent rocks in the world.

The museum was started by brothers Richard and Robert Hauck in 1990 in the shuttered Sterling Hill zinc mine, which had closed three years earlier. The mine was one of the oldest in the United States and began operation around 1739, and over its lifespan, it produced more than 11 million tons of zinc ore. When it closed, it was the last operating mine in the state of New Jersey.

Today the mine welcomes thousands of visitors into its depth each year to witness, among other things, its striking collection of more than 700 fluorescent objects. These objects—all able to glow under ultraviolet light, X-rays, or electron beams—illustrate a phenomenon that should be pretty familiar to anyone who’s had a black-light poster. The displays feature minerals, fossils, crystals, glass, fabric, and concrete, among others, all lit by ultraviolet light to show their glowing qualities.

In 1999, the museum created a special wing known as the Thomas S. Warren Museum of Fluorescence to house its glowing collection. It is named in honor of Thomas S. Warren, an ultraviolet researcher, and designer of the mineralight, a portable black-light lamp. The mine was placed on both the New Jersey Register of Historic Places and the National Register of Historic Places in 1991.