Question

Which of the following minerals will NOT scratch glass?

A. quartz
B. topaz
C. orthoclase feldspar
D. fluorite

Answer 1

Fluorite, with a hardness of 4 on the Mohs scale, will NOT scratch glass which has a hardness of about 5.5. Thus, the correct answer is D. fluorite.

Step-by-step explanation:

To determine which of the following minerals will NOT scratch glass, we must refer to the Mohs scale of mineral hardness, which ranks minerals based on their ability to scratch another material. On the Mohs scale, glass has a hardness of about 5.5. Therefore, a mineral must have a hardness of less than 5.5 to not be able to scratch glass.

• Quartz has a hardness of 7, so it can scratch glass.
• Topaz has a hardness of 8, so it also can scratch glass.
• Orthoclase feldspar has a hardness of around 6, which means it is capable of scratching glass.
• Fluorite has a hardness of 4, meaning it will NOT scratch glass as it is softer than glass.

Therefore, the correct answer is D. fluorite.

Answer 2

The answer is fluorite. If a mineral cannot be scratched by a knife blade but can be scratched by quartz then its hardness is between 5 and 7 on mohs scale. A relative hardness value of 6.5 means that the mineral could scratch orthoclase but not quartz. Flourite hardness on mohs scale is 4, and therefore due to the very low hardness and perfect cleavage of Flourite, special care must be taken to ensure it doesn't get scratched or chipped. It cannot scratch the glass.