Clay minerals — ordering soils by silica content Arrange the following clay types in order of increasing percentage of silica (SiO₂):

Introduction / Context:
Clayey materials used in bricks, tiles, and ceramics vary in silica and lime content. Silica affects refractoriness and shrinkage, while lime influences fluxing and fusibility. Correct ordering by silica content guides blend design for brick earths and ceramic bodies.

Given Data / Assumptions:

• Calcareous clay: higher CaCO3, comparatively lower SiO2.
• Pure clay (kaolinitic): balanced alumina and silica per mineral stoichiometry.
• Sandy clay: clay matrix with added sand (quartz), raising overall SiO2.

Concept / Approach:
Silica rises when free quartz (sand) is present; thus sandy clay ranks highest. Calcareous clay, richer in lime, ranks lowest in silica proportion. Pure clay lies between these extremes. This ordering is commonly referenced in brick-earth composition guidelines to control plasticity, drying shrinkage, and firing behavior.

Step-by-Step Solution:
Identify lowest SiO2: calcareous clay (lime-rich).Middle SiO2: pure clay (intrinsic aluminosilicate lattice).Highest SiO2: sandy clay (free sand elevates silica).Thus the correct increasing order is: Calcareous clay → Pure clay → Sandy clay.

Verification / Alternative check:
Lab XRF or oxide analysis of representative samples would confirm higher SiO2 in sandy mixes and lower SiO2 where CaCO3 dominates.

Why Other Options Are Wrong:
Any sequence placing sandy clay before calcareous clay in silica content contradicts the known effect of added quartz.

Common Pitfalls:
Confusing “plasticity” with “silica content,” or assuming all clays have similar silica simply because they are fine-grained.

Final Answer:
Calcareous clay → Pure clay → Sandy clay