Mineralogy — Sulfate Class Identification The sulfate minerals are defined as those containing one or more metallic elements chemically combined with the sulfate anion. Complete the definition by choosing the correct chemical group for “sulfate”: ____

Introduction / Context:
Mineral classes are grouped by their dominant anion or anionic complex. Recognizing the correct anion for sulfates is a foundational mineralogy skill that helps you quickly place a mineral in the right family and anticipate its properties and occurrences (for example, evaporite settings for many sulfates).

Given Data / Assumptions:

• Sulfate minerals contain the sulfate anion bonded to metal cations.
• We must pick the correct chemical formula fragment representing the sulfate anion.
• Common confusions include mixing up sulfates (SO4) with sulfites (SO3) or simple sulfur oxides (SO2).

Concept / Approach:
The sulfate anion is tetrahedral and written as SO4 (formally SO4^2-). Typical sulfate minerals include gypsum (CaSO4·2H2O), anhydrite (CaSO4), and barite (BaSO4). In contrast, the sulfite anion is SO3 (formally SO3^2-), which defines a different class; SO2 and SO are molecular/empirical formulas for sulfur oxides, not mineral anionic groups. Thus, SO4 is the only correct completion for the sulfate definition.

Step-by-Step Solution:

Verification / Alternative check:
Textbook examples: gypsum (CaSO4·2H2O) and barite (BaSO4) both clearly feature SO4 units, confirming SO4 as the correct choice.

Why Other Options Are Wrong:

• SO3: Defines sulfites, not sulfates.
• SO2: Gas; not the defining anionic group of a mineral class.
• SO: Not a standard mineral anion group.

Common Pitfalls:
Reading too fast and choosing SO3 because it “looks right.” Always distinguish sulfate (SO4) from sulfite (SO3).

Final Answer:
SO4