How to Streak a Mineral

All quartz, including amethyst, leaves a white streak.

Ever wonder how to tell the difference between fool's gold (pyrite) and real gold? One way is to crush some of the sample into powder. Often the color of the powder is different from the color of the mineral itself. An alternative is to do a streak test. Rather than pulverizing the entire sample, you turn a small portion into powder with the help of a streak plate. Streak plates are unglazed porcelain, preferably white.

Things You'll Need

• Towel
• Unglazed white porcelain

Instructions

1. Clean with water and dry both the streak plate and the mineral you're going to test. This will prevent contaminating the streak result.

2. Drag a pointed edge of the mineral across the streak plate, applying light pressure. To avoid damaging the mineral, push against the plate just hard enough to create a streak of mineral powder.

3. Compare the color of the streak to a list, database or chart of mineral streak colors. Consider the streak color as well as other identifying characteristics, such as hardness and density, to identify the mineral.

Tips & Warnings

• Not all minerals leave a streak color. This is only one aspect of identifying the mineral.

• You cannot use this method for some minerals because they are harder than the streak plate. This results in a damaged plate rather than mineral powder. If you get white powder, check the plate to see if it came from the porcelain rather than the mineral.

References

• Utah State Office of Education; Identifying and Classifying Minerals; Glen Westbroek; July 2000
• Mineralogical Society of America: The Mineral Identification Key

Resources

• Mineralogy Database: Streak Colors