Mineral Hardness (page 2)

Mineral Ranks

Minerals can be identified by a variety of characteristics, but one of the most useful ways is to test their hardness. Hardness is the measure of the resistance of a mineral to being scratched. Geologists use a standard hardness called the Mohs scale to rank minerals from 1 (softest) to 10 (hardest). The scale indicates which common objects can scratch certain minerals. If you are just comparing the hardness of minerals with each other, you can do so without using the Mohs scale. Just remember a harder mineral is capable of scratching a softer mineral, and a softer mineral may leave a streak on the harder mineral. In this activity you will arrange five unidentified minerals in order of hardness, from softest to hardest.

Materials

Cup containing five unidentified minerals of different hardness. Label each minerals as A, B, C, D, or E.  Minerals that could be used in this experiment include talc, gypsum, fluorite, calcite, and quartz.

Pencil

Paper plate

Activity

1. Empty the minerals from the cup onto the paper plate.
2. Your task is to arrange the minerals in order, starting with the softest mineral and ending with the hardest mineral.
   1. Rub any two minerals together and see which of the two is capable of scratching the other mineral. (Note: After rubbing two minerals together, rub your finger over the mark left on one to determine whether the mark is a scratch or a streak. A streak can be rubbed off, but a scratch cannot.)
   2. Continue this process until you are able to rank the minerals from softest to hardest.

Follow-Up Questions

1. What was the softest mineral? What was the hardest?
2. Based on the scratch and streak test, list the minerals you examined in this activity from softest to hardest.
3. Look at the Mohs scale in Figure 12.1. Which mineral can be scratched with your fingernail?

Answers

1. Answers will vary.
2. Answers will vary.
3. Talc.

Extension

Using the Mohs scale and some common objects you have on hand, attempt to determine the actual hardness of the five minerals you ranked today.