Which properties are used to identify minerals, and why might streak not be reliable on all minerals?

• A. Size, density, magnetic property
• B. Hardness, luster, color, streak, and cleavage/fracture; streak can be unreliable for some minerals or metal-rich samples.
• C. Taste and smell
• D. Color alone; color is always reliable

Answer: (B)

Mineral identification relies on several physical properties that stay with the mineral, even when it’s in different forms. Hardness tells you how easily it can be scratched, luster describes how it reflects light, color is what you see on the surface, streak is the color of the mineral’s powder when it’s rubbed on a porcelain plate, and cleavage or fracture shows how it breaks. Color by itself can be misleading because impurities, weathering, or coatings can change what the mineral looks like on the outside, so you can’t rely on color alone.

Streak adds useful information because it reveals the color of the mineral’s powder, which often stays more constant than surface color. But streak isn’t perfect for every mineral. Many minerals share the same powder color, so the streak doesn’t distinguish them well. Some minerals have surface colors that don’t match their powder color, or they’re so hard that creating a usable powder on a standard plate is difficult, making the streak test unreliable. That’s why relying on a combination of properties gives a more accurate identification.