For the majority of minerals,the streak obtained when the mineral is scratched against a porcelain plate is
A) only useful if the mineral is softer than the porcelain streak plate.
B) always diagnostic of that mineral.
C) not useful,because the porcelain will often chemically react with the mineral.
D) always dark brown or black.

Question

Quizplus · Accepted Answer

Streak tests are only useful for minerals softer than the porcelain streak plate because the mineral must leave a powder on the plate to observe its color. If the mineral is harder than the plate, it won't leave a streak.

For the Majority of Minerals,the Streak Obtained When the Mineral