Question

Analyze the following statements based on the provided classification:

1. Vitreous, Pearly, and Silky are sub-types of Non-metallic lustre.
2. Talc is identified as having a resinous lustre in the provided table.
3. The capacity to absorb light has no influence on the appearance of lustre.

• A. All
• B. i, iii
• C. i only
• D. i, ii

Answer 1

Answer:

D. i, ii

Mineral Lustre

1. Classification of Non-metallic Lustre:

• Statement (i) is correct. Vitreous (glass-like), pearly (like a pearl), and silky (like silk) are indeed recognized sub-types of non-metallic lustre. Lustre describes how light reflects off the surface of a mineral. Non-metallic minerals exhibit a wide range of non-metallic lusters, including these examples.

• Other common non-metallic lusters include:

  • Earthy or Dull: Lacking any shine.

  • Greasy: Appearing coated with oil.

  • Resinous: Similar to the lustre of resin.

  • Waxy: Resembling wax.

2. Lustre of Talc:

• Statement (ii) is correct. The table classifies Talc as having a resinous lustre. While Talc is often described as having a greasy or soapy feel due to its softness (Mohs hardness of 1), its visual appearance can be interpreted as having a resinous quality under certain lighting conditions. Some sources also describe it as waxy or pearly. The classification in the provided context identifies it as resinous.

3. Influence of Light Absorption on Lustre:

• Statement (iii) is incorrect. The capacity to absorb light significantly influences the appearance of lustre. The degree to which a mineral reflects or absorbs light determines whether its lustre is described as metallic, vitreous, dull, etc. Minerals that absorb most light appear dull, while those that reflect most light exhibit a brighter lustre. Lustre is fundamentally a visual property dependent on light interaction.