Ganister (a siliceous rock) is primarily a source of which refractory-forming oxide?

Introduction / Context:
Raw materials for refractories include natural minerals and rocks rich in the target oxides. Ganister is a traditional term in refractory practice—knowing what oxide it provides helps understand historic silica-lining practice.

Given Data / Assumptions:

• Ganister is siliceous (high SiO2 content).
• Used historically in acid linings.
• Question asks for the principal oxide supplied.

Concept / Approach:
Ganister is a hard, fine-grained silica rock used as a source of SiO2 for acid refractories. It has been used for silica bricks and ramming mixes in acid steelmaking applications.

Step-by-Step Solution:
Identify ganister as siliceous → supplies SiO2.Exclude MgO and CaO: those are basic oxides from different raw materials.Select Silica (SiO2).

Verification / Alternative check:
Textbooks list ganister among silica sources for acid refractories.

Why Other Options Are Wrong:
MgO/CaO/Al2O3: not the main constituents of ganister.None of these: incorrect since SiO2 applies.

Common Pitfalls:
Confusing ganister with gahnite or other similarly named minerals.

Final Answer:
Silica (SiO2)