Allison and Roberto Mignone Halls of Gems and Minerals

True Colors

The Sterling Hill Mine operated between 1850 and 1986, producing 11 million tons of unusually rich zinc ore. It wasn’t until the early 1900s that the mine’s true colors shone, when sparks from a flickering electric lamp revealed the fluorescent minerals in the ore’s body.

Excited Electrons

Exposure to ultraviolet (UV) light excites electrons in the minerals. When this high energy is released, for some minerals, it is released as light in the lower-energy visible spectrum: fluorescence. Under long-wave UV, calcite appears pale pink and the willemite is pale green. 

Short and Sweet

Short-wave UV light travels at a higher frequency and energy than longwave UV. Because of this difference, the color and intensity of light released during fluorescence may also change. Calcite in the slab fluoresces bright red-orange and willemite glows intense green.

Building Blocks

The large stibnite crystals are made up of tiny building blocks called unit cells, in which atoms and sulfur combine in a regular arrangement. Unit cells repeat in a 3D pattern to form a crystal.

Rare Find

Stibnite (Sb2S3), a compound of the elements antimony and sulfur, occasionally forms nests of delicate, swordlike crystals, but examples this large and intricate are exceedingly rare.

Water Wonder

Hydrothermal processes like the one that formed this stibnite require hot water, which dissolves mineral components and transports them along fractures and through porous rocks.

Explosive Origins

This ancient stibnite formed in southeastern China, the site of extensive volcanic activity some 130 million years ago. 

Sparkly Stone

This mineral’s iridescence comes from light scattering from submicroscopic layers within individual labradorite crystals.

Colossal Crystals

This specimen boasts very large crystals—some of them measure up to a yard (1 meter) long!

Made in Madagascar

This specimen comes from a huge igneous intrusion that formed when tectonic plates collided between 630 million and 550 million years ago.

Best Angle

Most objects absorb some colors from white light and reflect the color you see. The surface of this specimen absorbs most of the colors of light, so it looks gray—until you’re at the proper angle to see the colorful light scatter.

Purple For Now

It took millions of years for these crystals to turn from colorless quart to purple amethyst quartz. Natural, high-energy radiation from the hosting rocks caused the color, which intensified with time and exposure.

Lots of Layers

In addition to purple amethyst quartz, this geode has a layered rim of white, gray, and brown chalcedony, a variety of quartz with ultra small crystals.

Heavy Duty

This geode weighs around 11,000 pounds (5,000 kg), more than its sibling specimen—which is taller but lighter, at 9,040 pounds (4,100 kg).

Dissolving Limestone

Weak acids in rain and groundwater dissolve carbonate minerals such as calcite, the primary material in limestone rock that hosted this block. Over millions of years, dissolution of limestone bedrock can form dramatic caves.

Colorful Crystals

Crystals of bright green malachite and deep blue azurite can be seen in this block’s cavities. These formed when acidic, copper-rich fluids flowed through cracks in the original limestone and deposited azurite, malachite, and some iron oxides.

Counting Copper

This roughly 7,200-lb (3,300 kg) block contains around 3,400 pounds (1,500 kg) of copper—enough to wire 17 single-family homes with electricity.

Sing a Song

For years, this spectacular specimen made high-pitched sounds when the humidity changed with the seasons, as the porous stone absorbed and released moisture from the air. Now that it is in a controlled environment, it has stopped singing.

Rare Metal

In addition to forming giant crystals, many pegmatites have minerals that concentrate rare elements, like beryllium (Be) in beryl.  

Space Mirrors

Beryl is an important source of beryllium, which is light and stiff with a relatively high melting point. These properties make it useful in aerospace materials, including in mirrors for the James Webb Space Telescope.

One of Ten

This big beryl comes from the Bumpus Quarry in Albany, Maine. It was one of 10 enormous beryls that measured up to 19 feet (5.8 m) long and 4 feet (1.2 m) across.

Preserved by Volcanoes

When this dawn redwood was buried, an early volcanic arc was forming as an ocean tectonic plate subducted under western North America. Volcanoes erupted violently and deposited thick layers of volcanic ash, burying the forest.

Big Range

This dawn redwood lived about 35 million years ago in the present-day Cascade Mountains. Earth’s climate was warmer and wetter then, and the range of the dawn redwood extended above the Arctic Circle.

Extinct in the USA

Today, native dawn redwoods grow only in a few forests in China. It’s likely their extinction in North America had many causes, including a change in climate change, ecological shifts, and modifications in global topography.

Count the Rings

The rings of this fossil dawn redwood were preserved during fossilization, so that you can count them to estimate how long it lived. Though some rings have become distorted over millions of years, experts have counted up to 884 individual bands.

Made in New York

This towering slab studded with garnets of up to 1 foot across comes from New York’s Gore Mountain in the Adirondack Mountains.

Feeling Sharp

These garnets are unusual because they are cracked along many parallel planes—which makes them perfect as an abrasive, like sandpaper.

Under Pressure

The garnets resulted when rock transformed at pressure 8,000 times greater than atmospheric pressure (and at about 1500° F (815° C).

Moving Pieces

During metamorphic reactions that formed these garnets, elements moved between solid minerals via chemical diffusion.