Question

If a mineral scratches an iron nail but doesn’t scratch a streak plate, what could its hardness be on the Mohs scale?

Mineral Name Mohs Hardness Scale Approximate Hardness of Common Objects
Talc 1
Gypsum 2 Fingernail (2.5)
Calcite 3 Copper Penny (3.5)
Fluorite 4 Iron Nail (4.5)
Apatite 5 Glass (5.5)
Orthoclase 6 Steel File (6.5)
Quartz 7 Streak Plate (7.0)
Topaz 8
Corundum 9
Responses

3
3

4.5
4.5

5
5

7
7

Answer 1

To determine the hardness of the mineral in question, we can refer to the provided information about its ability to scratch an iron nail but not a streak plate.

1. The hardness of an iron nail is approximately 4.5 on the Mohs scale.
2. The hardness of a streak plate is approximately 7.0 on the Mohs scale.

Since the mineral can scratch the iron nail (hardness 4.5), it must have a hardness greater than 4.5. However, since it cannot scratch the streak plate (hardness 7.0), its hardness must be less than 7.0.

Therefore, the possible range for the hardness of the mineral is between 4.5 and 7.0. Based on the Mohs scale, the only integer value in this range is 5.

The mineral's hardness is likely **5** on the Mohs scale.