Questions: Mineral Properties and Testing

Question 1

A student finds a golden-colored mineral and thinks it might be gold. Which property test would be MOST helpful in telling real gold from fool's gold (pyrite)?

• A. Color — real gold is more yellow
• B. Streak — gold leaves a golden streak while pyrite leaves a greenish-black streak
• C. Size — real gold nuggets are always bigger
• D. Weight alone — just hold them in your hand

Answer: (B)

Streak is one of the most diagnostic tests. When rubbed on a streak plate, gold leaves a golden-yellow streak, while pyrite (fool's gold) leaves a greenish-black streak. Color alone is unreliable because both look golden on the surface.

Question 2

On the Mohs hardness scale, a mineral with a hardness of 7 can scratch a mineral with a hardness of 5, but a mineral of 5 cannot scratch a mineral of 7.

• T. True
• F. False

Answer: True

The Mohs scale ranks scratch resistance. A harder mineral always scratches a softer one, never the reverse. Quartz (7) will scratch apatite (5), but apatite cannot scratch quartz.

Question 3

What is the difference between a mineral's cleavage and fracture?

Model answer: Cleavage is when a mineral breaks along smooth, flat planes because of its crystal structure (like mica splitting into thin sheets). Fracture is when a mineral breaks along rough, irregular surfaces with no flat planes (like quartz shattering into curved, shell-like pieces).

Whether a mineral shows cleavage or fracture depends on how its atoms are bonded. If there are weak planes in the crystal structure, the mineral cleaves along them. If bonds are equally strong in all directions, the mineral fractures irregularly.