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  • A close up of the Black Sand exhibit
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  • At Black Sand, see the shape of an invisible magnetic field.

  • Exhibit developer Richard Gagnon explains how the exhibit came to be and how it's taken care of.
  • Big magnets and black sand were made for play.

  • Explore the mysteries of Ocean Beach's black sand (a.k.a. magnetite). 

  • A close up of the Black Sand exhibit
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  • Black Sand | 2018
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  • Science in the City: Black Sand

Black Sand

Get your hands into magnetic sand.

At this simple but ever-popular exhibit, black sand from nearby beaches make spiky patterns that reveal the invisible magnetic field between the poles of two giant magnets.


Where:   Ray and Dagmar Dolby Atrium
Exhibit Developer:   Richard Gagnon, 1977

What’s going on?

The black sand at this exhibit is magnetite, a naturally occurring iron oxide mineral found in almost all igneous and metamorphic rocks.

The black sand we use at this exhibit comes from nearby Ocean Beach—but it originates in the Sierra Nevada Mountains to the east. There, granite containing iron ore breaks down into tiny grains of black sand that then erode, getting carried by rivers to San Francisco Bay and beyond.

Not usually magnetic in and of itself, black sand can and will become magnetized in the presence of another magnet. As each tiny grain of magnetized black sand becomes a (temporary) magnet itself, the magnetic field in that spot gets amplified, and more black sand gets attracted—ultimately creating the porcupine-like spikes that you see here.

 
Phenomena: Electromagnetic Forces, Ferromagnetism, Magnetization
Keywords: magnetic field, sand
Aliases: Magnetic Sand
Collections: Young Kids

More to explore

Exhibits In Extreme Close Up: Black Sand

by Paul Dancstep • April 7, 2017

A science activity that makes the patterns of a magnetic field visible
Magnetic Lines of Force

Iron filings trace out magnetic field lines in three dimensions.

Field Trip Chaperone Guide: Exploring Magnets
Field Trip Chaperone Guide: Exploring Magnets

Based on third-grade NGSS standards; appropriate for grades 2–5

Rolling Through the Bay
PlayList: Greatest Hits: Gallery 2

At the museum? Try some of our favorite exhibits.

Related exhibits

Magnet + Electricity = Motor
Magnet + Electricity = Motor

This exhibit demonstrates the principles by which a motor functions.

Magnetic Clouds
Magnetic Clouds

"Clouds" of iron particles dart and dance in a magnetic field.

Circles of Magnetism
Circles of Magnetism

Electricity moving in a wire makes a circular magnetic field.

Circuit Workbench
Circuit Workbench

Try building these circuits found in everyday objects.


IMLS acknowledgment

This web project was made possible in part by the Institute of Museum and Library Services [MA-30-16-0175-16].

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