Paint formulation — which of the following is generally NOT used as an extender (filler) in paints? Pick the exception.

Introduction / Context:
Paints contain pigments for color and opacity, extenders (fillers) to control gloss, texture, and cost, and binders/solvents to form the film. Extenders are usually inert, low-cost mineral powders that improve body and application properties but contribute little to opacity or tint strength compared with true pigments. This question asks you to identify which listed material is not generally used as an extender.

Given Data / Assumptions:

• Common extenders include silica, talc, gypsum, barytes, and china clay.
• True pigments provide strong hiding power and color.
• We are considering general architectural/industrial paint practice.

Concept / Approach:
Extenders (functional fillers) modify rheology, reduce cost, and adjust sheen; they are usually chemically inert and pale. Zinc white (zinc oxide), however, is a traditional white pigment with distinct hiding power, mildewcide action, and UV stability roles; it is not merely a cheap filler. Therefore it is the exception among mainly extender-grade minerals listed.

Step-by-Step Solution:

Verification / Alternative check:
Coatings handbooks categorize zinc oxide as pigment; extenders include calcium carbonate, silica, talc, kaolin, and barytes.

Why Other Options Are Wrong:

• Powdered silica: Standard extender for matting and reinforcement.
• Gypsum: Calcium sulfate used as a filler/extender.
• Talc: Lamellar mineral widely used as extender and anti-sag aid.

Common Pitfalls:
Confusing pigment-grade white materials with inert extenders; the key is opacity and specific functionality.

Final Answer:
Zinc white