Book 27, Question 79
What is a streak test?
A streak test rubs a mineral across a rough, white, unglazed porcelain tile to leave a line of powder.
The color of the powder can be different from the color of the mineral. Hematite looks silver or black but leaves a reddish-brown streak, and pyrite leaves a greenish-black one. Streak color is often more reliable than the outside color for identifying minerals.