Question

Which structure has lens-like shaped structure?

(a) Cataclastic structure

(b) Schistose structure

(c) Augen structure

(d) Maculose structure

The question was posed to me in an internship interview.

My query is from Structures of Metamorphic Rocks in portion The Study of Rocks of Engineering Geology

Answer 1

The correct answer is:

(c) Augen structure

Explanation: An Augen structure refers to a lens-like or eye-shaped structure found in metamorphic rocks, particularly in schist or gneiss. The term "Augen" is derived from the German word for "eyes," describing the appearance of large, rounded mineral grains (often feldspar) that are surrounded by a finer-grained matrix. These lens-shaped structures are typically formed under high-grade metamorphic conditions.

Here’s a brief overview of the other options:

• Cataclastic structure: This structure is associated with rocks that have undergone intense mechanical deformation, often resulting in fragmented or crushed grains.
• Schistose structure: Refers to a foliated texture found in schist, where minerals are aligned in parallel planes, but does not specifically describe a lens-like shape.
• Maculose structure: Refers to a structure in which minerals appear as spots or patches, but not lens-shaped.

So, Augen structure is the correct answer as it specifically refers to a lens-like shape in the mineral fabric of the rock.