Molten materials cool at different rates. Which physical property of a mineral is most directly affected by the rate of cooling?

• A. Color
• B. Crystal size
• C. Hardness
• D. Density

Answer: (B)

Verified step by step guidance

1. Understand that when molten material cools, the rate of cooling influences how atoms arrange themselves as the material solidifies.
2. Recognize that a slower cooling rate allows atoms more time to organize into larger, well-formed crystals, while rapid cooling results in smaller crystals.
3. Recall that crystal size is a physical property describing the size of the individual crystals in a mineral, which directly depends on the cooling rate.
4. Note that other properties like color, hardness, and density are less directly influenced by cooling rate and more by chemical composition and bonding.
5. Conclude that the physical property most directly affected by the rate of cooling is the crystal size.