Experiments with Quartz
Experiments you can do
Big word, but not so hard to say:
TRY- bo - lumen - essence.
Luminescence is light or a glow. Triboluminescence is light that is produced by pressure, friction, or mechanical shock. It may be readily demonstrated with two hand-sized milky quartz crystals in a darkened room. Simply take the edge of one crystal and rub it back and forth on the face of the other crystal. You may simply rub two faces of the crystal together, but you get more light using the former method. You can also knock together two milky quartz pebbles of landscape rocks. An orange-yellow light can be seen inside the crystal. You will also notice a metallic smell. This makes a good classroom demonstration!
I have also heard that the same effect can be seen by pinching sugar cubes with a pair of pliers, or crunching Wintergreen Lifesavers with your mouth open in a dark room. I haven't tried it... if it works for you, let me know!
The piezioelectric effect was first observed in the laboratory. Several minerals, including tourmaline and sphalerite, also exhibit this effect.
Electricity is electrons in motion. A small electric pulse can be generated from some crystals whose atomic arrangement allows the electrons to move in certain directions, and quartz is one of the minerals that have this property. The flow of electrons is caused by a change in the shape of the crystal, which can be induced mechanically or thermally.
In this setup, we attached cardiac monitoring electrodes to the sides of a quartz crystal, and connected them to a meter. We protected the surface of the crystal with a piece of cardboard, and then tapped the flat surface of the crystal with a hammer. Sure enough, the meter registered a small spike.
An alternate method to show the piezoelectric effect is to heat a fair sized quartz crystal in an iron skillet, which sets up mechanical stress due to uneven heating. This changing mechanical stress will generate electricity in the crystal, just like that caused by mechanical shock.
The key to producing the current is the change in the shape of the crystal. A pressure will cause a pulse, but continued pressure will not effect a sustained flow of electrons. Although it appears electricity can be squeezed out of a crystal, that is not the case. When you alternately apply and release pressure on a quartz crystal, during the pressure changes on the structure a small amount of electron flow is created. So by applying cyclic pressure, a current may be generated. Conversely, when a small amount of electricity is applied to a crystal, the internal structure changes shape, or vibrates. This principle is involved in the manufacture of highly accurate quartz watches and quartz tuners on stereo systems.