Question

Evaluate these statements regarding specific minerals and their lustre:

1. Muscovite exhibits a pearly lustre, which is described as the shine of pearls
2. Quartz and Zircon both fall under the category of Vitreous lustre.
3. Metallic lustre is defined as the shine of metal.

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

Answer 1

Answer:

A. i, iii

Mineral Lustre:

Understanding Lustre in Minerals

• Mineral lustre refers to the way light reflects off the surface of a mineral. It's a key characteristic used in mineral identification.

• Lustre is broadly categorized into two main types: Metallic and Non-metallic.

Metallic Lustre

• Minerals with a metallic lustre have a surface that resembles polished metal. This type of lustre is typically opaque and reflects light strongly.

• Examples of minerals exhibiting metallic lustre include Pyrite (often called 'fool's gold'), Galena, and Magnetite.

Non-metallic Lustre

• This category encompasses a wide range of reflective qualities, distinct from metallic shine. It is further subdivided into several types:

  • Vitreous Lustre: This is the most common type of non-metallic lustre and resembles the shine of broken glass.

  • Examples of Vitreous Lustre: Quartz, Topaz, Feldspar, and Beryl.

  • Pearly Lustre: This lustre is characteristic of minerals that have a pearly sheen, similar to the iridescent surface of a pearl. It often appears on cleavage surfaces.

  • Example of Pearly Lustre: Muscovite (a type of mica) is a classic example exhibiting pearly lustre. Talc can also show this.

  • Resinous Lustre: This lustre resembles the shine of resin or plastic. Sulfur is a common example.

  • Waxy Lustre: Minerals with a waxy lustre appear as though coated in wax. Chalcedony can exhibit this.

  • Greasy Lustre: This lustre gives the mineral the appearance of being coated in oil or grease. Nepheline and some Quartz varieties show this.

Statement Analysis

• Statement i: Muscovite exhibits a pearly lustre, which is described as the shine of pearls. This statement is correct. Muscovite is a well-known example of a mineral with pearly lustre.

• Statement ii: Quartz and Zircon both fall under the category of Vitreous lustre. This statement is correct. Both Quartz and Zircon are typically characterized by their vitreous (glass-like) lustre.

• Statement iii: Metallic lustre is defined as the shine of metal. This statement is correct. This is the fundamental definition of metallic lustre in mineralogy