Rock Identifier
Efflorescence (on Clay Brick) (Crystalline salt deposits (typically Sodium Sulfate Na2SO4, Calcium Carbonate CaCO3, or Potassium Sulfate K2SO4)) — Mineral precipitate (anthropogenic context)
Mineral precipitate (anthropogenic context)

Efflorescence (on Clay Brick)

Crystalline salt deposits (typically Sodium Sulfate Na2SO4, Calcium Carbonate CaCO3, or Potassium Sulfate K2SO4)

Hardness: 1.5–3 (Mohs scale); Color: White or grayish-white; Luster: Dull to powdery; Crystal structure: Usually orthorhombic or monoclinic (as micro-crystals); Cleavage: Perfect (on individual crystals but rarely seen in deposits); Specific gravity: 2.6–2.7

Hardness
1
Color
White or grayish-white
Luster
Dull to powdery
Identified More mineral precipitate (anthropogenic context) →

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Physical properties

Hardness: 1.5–3 (Mohs scale); Color: White or grayish-white; Luster: Dull to powdery; Crystal structure: Usually orthorhombic or monoclinic (as micro-crystals); Cleavage: Perfect (on individual crystals but rarely seen in deposits); Specific gravity: 2.6–2.7

Formation & geological history

Formed through the secondary process of salt migration. Soluble salts within the brick or mortar are dissolved by water; as moisture evaporates from the surface, the salts are left behind as a crystalline deposit. This happens frequently in masonry exposed to high moisture.

Uses & applications

In this context, it has no industrial use; it is considered a cosmetic defect in construction. However, the constituent salts (like sodium sulfate) are used in glass manufacturing and detergents.

Geological facts

Efflorescence is often mistaken for mold, but unlike mold, it will turn into powder when pinched and will dissolve in water. It is a major indicator of moisture infiltration issues in building envelopes.

Field identification & locations

Identify in the field by its white, powdery appearance on masonry surfaces. It can be found globally on any brick, concrete, or stone structure exposed to wetting and drying cycles. Collectible value is effectively zero as it is a common building byproduct.

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