What term refers to visible features on the surface of a mineral crystal that reflect its internal growth and development?

What term refers to visible features on the surface of a mineral crystal that reflect its internal growth and development?

• A. Graining (Grain Lines)
• B. Growth Marks
• C. Point Defect
• D. Singly Refractive (Isotropic)

Answer: (B)

Growth marks are the visible features on a crystal surface that record how the crystal grew over time. As a mineral forms, its faces accumulate growth increments; changes in growth conditions, speed, or environment leave lines, bands, or ridges that trace the crystal’s developmental history. These surface features reveal the sequence and nature of growth, much like rings in a tree show its life history. This concept is distinct from point defects, which are tiny atomic-scale flaws inside the lattice, and from isotropy, which describes how light travels through the crystal rather than providing a record of growth. Graining can relate to surface texture from internal orientation, but growth marks specifically denote the growth history reflected on the surface.

Growth marks are the visible features on a crystal surface that record how the crystal grew over time. As a mineral forms, its faces accumulate growth increments; changes in growth conditions, speed, or environment leave lines, bands, or ridges that trace the crystal’s developmental history. These surface features reveal the sequence and nature of growth, much like rings in a tree show its life history. This concept is distinct from point defects, which are tiny atomic-scale flaws inside the lattice, and from isotropy, which describes how light travels through the crystal rather than providing a record of growth. Graining can relate to surface texture from internal orientation, but growth marks specifically denote the growth history reflected on the surface.