Question - You have an unknown mineral that can scratch glass but cannot scratch a porcelain streak plate. What is its approximate hardness?

You have an unknown mineral that can scratch glass but cannot scratch a porcelain streak plate. What is its approximate hardness?

ANSWER:

Glass has a Mohs hardness of about 5.5 while porcelain is close to 6.5. The mineral is be‐ tween these two, so it must be close to 6.