Which mineral property is determined by rubbing it on a rough surface?

Which mineral property is determined by rubbing it on a rough surface?

• A. Mohs hardness
• B. Color
• C. Streak
• D. Luster

Answer: (C)

Streak is the color of the powder left when a mineral is rubbed on an unglazed, rough surface. Rubbing removes a thin layer of the mineral and reveals its true powder color, which is often more diagnostic than the surface color that can be altered by impurities, weathering, or tarnish. This makes streak the best way to describe a mineral’s color in terms of a consistent property. In contrast, hardness is about scratch resistance, color is the mineral’s surface hue, and luster is how the surface reflects light.

Streak is the color of the powder left when a mineral is rubbed on an unglazed, rough surface. Rubbing removes a thin layer of the mineral and reveals its true powder color, which is often more diagnostic than the surface color that can be altered by impurities, weathering, or tarnish. This makes streak the best way to describe a mineral’s color in terms of a consistent property. In contrast, hardness is about scratch resistance, color is the mineral’s surface hue, and luster is how the surface reflects light.