Question

Evaluate the following statements about mineral characteristics:

1. "Streak" and "Color" are always identical for any given mineral.
2. "Fracture" refers to the way a mineral breaks when it does not exhibit cleavage.
3. Specific gravity is a measure of a mineral's relative density.

• A. All
• B. i, iii
• C. i only
• D. None of these

Answer 1

Answer:

B. i, iii

Mineral Characteristics Explained for Competitive Exams

Understanding Mineral Properties:

• Color vs. Streak:

  • Color is the most obvious visual characteristic of a mineral, but it can be highly variable due to impurities or different formation conditions. For example, quartz can be found in many colors (clear, white, pink, purple, grey, black).

  • Streak is the color of a mineral's powder when it is ground against an unglazed porcelain plate (streak plate). The streak is a much more reliable identifying property than color because it is constant for a particular mineral.

  • Statement i is incorrect because color and streak are not always identical. For instance, Hematite is typically silver-grey or black in color but has a reddish-brown streak.

• Fracture and Cleavage:

  • Cleavage is the tendency of a mineral to break along specific, flat planes of weakness related to its atomic structure. Minerals with cleavage break into smooth, flat surfaces.

  • Fracture describes how a mineral breaks when it does not break along cleavage planes. It refers to the irregular or rough surfaces produced. Common types of fracture include conchoidal (shell-like, e.g., quartz), uneven (rough), and fibrous.

  • Statement ii is correct as fracture is indeed how minerals break when they lack cleavage or when broken across cleavage planes in an irregular manner.

• Specific Gravity:

  • Specific Gravity (SG) is the ratio of the density of a mineral to the density of water at 4°C. It is essentially a measure of how heavy a mineral is for its size, relative to water.

  • For example, minerals with an SG of 2.5 are 2.5 times denser than water.

  • Statement iii is correct because specific gravity quantifies a mineral's relative density.