What characteristics does Porcelain possess that makes it a good choice for the Streak test? Additionally, are there any other materials that could also be used for designing a Streak plate?
- It's white, so the streak colour is obvious.
- It's hard. Porcelain is made from aluminosilicates like sillimanite and mullite. Mohs hardness is around 7. Not many geological materials are harder than it, and streak is not a diagnostic feature for those that are harder.
- It's rough (i.e. unglazed) so it's really good in breaking tiny fragments from the tested material, thus producing the streak.
- It's cheap and widely available.