Amorphous vs crystalline — pick the amorphous material from the list Which of the following is an amorphous (non-crystalline, glassy) material at room temperature?

Introduction / Context:
Solid materials are broadly classified as crystalline or amorphous based on the presence or absence of long-range atomic order. Many physical properties—such as sharp melting point, anisotropy, and mechanical response—depend strongly on this structural distinction.

Given Data / Assumptions:

• Room-temperature phases of common engineering materials.
• Comparison among layered minerals, metals, and non-crystalline solids.

Concept / Approach:
Amorphous solids lack long-range periodicity; their atoms are arranged randomly, leading to broad glass transition rather than a sharp melting point. Commercial glass (e.g., soda-lime silica) is the archetypal amorphous material. In contrast, mica is a crystalline silicate with layered sheets; silver and lead are crystalline metals with well-defined lattices; graphite is crystalline with hexagonal layered structure (although it exhibits anisotropy and easy basal slip, it is not amorphous).

Step-by-Step Solution:

Verification / Alternative check:
Differential scanning calorimetry shows a glass transition for glass, whereas crystalline materials show sharp melting endotherms; X-ray diffraction yields broad halos for amorphous glass and sharp peaks for crystalline solids.

Why Other Options Are Wrong:

• Mica: layered crystalline silicate with cleavage along basal planes.
• Silver, lead: face-centered cubic (silver) and close-packed structures (lead has fcc) with crystalline order.
• Graphite: crystalline hexagonal layers with distinct basal planes.

Common Pitfalls:
Assuming visually transparent materials are always amorphous; quartz is transparent yet crystalline, whereas glass is amorphous.

Final Answer: