Image credit: Scott Brande
The Bottom Line on Electrical Conductance - Here on Top!
Most Metallic Minerals (and Graphite) Conduct Electricity
- A simple flashlight demonstrates that electrons moving through metal wires and connectors around a circuit powers and lights a bulb.
- A mineral sample may be inserted into the circuit of a cheap flashlight to test whether or not the mineral conducts electricity.
- Minerals of some (but not all) common metallic compounds conduct enough electricity to power a light bulb. These include native copper, pyrite, and galena (among others).
- Hematite is an insulator, and thus does not light a bulb.
Bottom Line: I created this test as a replacement for the traditional observation of luster to identify metallic minerals and distinguish them from non-metallic minerals. My students find the flashlight experiment fun and fast. The result is usually unequivocal, and a cheap flashlight (at "WallyWorld") costs only $1!
Errors/Suggestions: Contact Scott Brande (see footer)
Flashlight Components and Demonstrations
- flashlight contains a battery pack
- flashlight has metal strips or wires that conduct electricity between battery pack and bulb (electrical circuit)
- flashlight has a switch that opens or closes the circuit
Watch the video demonstrations below.
Flashlight Test of Copper Wire
Flashlight Test of US Penny
Flashlight Test of a Mineral
Instructions: How to Test for Electrical Conductance
Another property of some minerals is an ability to conduct electricity. Electrical conduction is due to the movement of electrons among atoms. This periodic table identifies elements that are termed metallic. Only a small number of minerals conduct electricity and can function like metal wires in electrical circuits. A simple flashlight can be used to test materials (including minerals) for electrical conduction.
Caution - The use of batteries requires caution, as when improperly oriented, they can cause a short-circuit.
Materials for test
- mineral sample
- a small working flashlight
Procedure for the test
- Watch the instructional video that demonstrates how a pencil can be inserted into a flashlight electrical circuit to demonstrate its ability to conduct electricity through the pencil core of "lead" (actually the mineral graphite)
- Remove the end cap of the flashlight.
- Position the mineral sample to touch both the metal contact on the battery holder, and the metal band or strip that leads inside the flashlight barrel to the bulb.
- Complete and break the circuit repeatedly.
- Observe the bulb for light emission.
Possible test results and interpretation
- The flashlight lights up when the sample completes the electrical circuit. We may conclude that the sample is composed of a conducting metallic element or mineral compound, or the non-metallic mineral graphite (which is a true conductor of electricity).
- The flashlight does not light up when the sample completes the electrical circuit. We cannot conclude that the sample lacks a metallic element or compound. The possible reasons for a failure are numerous - misaligned or poor contact between the sample and the flashlight components, weak batteries, a metallic compound or ore that has insufficient electrical conductivity to illuminate the bulb, a non-metallic compound, etc.
The only significant result of this test for mineral identification is when the bulb lights up. Then we may identify the sample as either graphite (same material as "pencil lead"), or one of a few other common metallic minerals.