Q1. [3] medium thorough-understanding
Bauxite is not found in veins and lodes, nor in sedimentary beds formed by compression. What process leads to the formation of bauxite deposits, and what does this tell us about the type of rocks from which it originates?
Generated by claude-sonnet-4-6 · 2026-06-26 13:33 · grounding rag
Model Answer
Bauxite deposits are formed through the decomposition of surface rocks. Soluble constituents are removed during weathering, leaving behind a residual mass of weathered material that contains the ore. This process tells us that bauxite originates from rocks rich in aluminium silicates — a wide variety of such rocks undergo decomposition to produce bauxite, a clay-like substance. Therefore, bauxite is a product of surface weathering rather than volcanic activity or sedimentary deposition.
Source: Chapter 5 — Minerals and Energy Resources, Mode of Occurrence of Minerals / Bauxite section
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Explanation
- The examiner wants two things: (1) the process — decomposition/weathering of surface rocks, removal of soluble parts, leaving residual mass; (2) the rock type — rocks rich in aluminium silicates.
- Do not confuse this with sedimentary minerals (formed by deposition) or igneous/metamorphic minerals (veins and lodes). Bauxite's formation mode is unique — it is a residual deposit.
- Keywords to use: decomposition, soluble constituents, residual mass, weathered material, aluminium silicates.