How to identify Laterite

To correctly identify Laterite (Laterite (iron-rich soil/rock)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically reddish-brown, orange-brown, or yellowish-brown due to iron oxides. Can also be mottled with white, gray, or purple.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Earthy to dull, sometimes sub-metallic in denser, iron-rich varieties.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Highly variable: earthy, porous, vesicular, pisolitic (pea-sized concretions), nodular, vermicular (worm-like structures), or massive. Often feels gritty due to fine-grained quartz or other resistant minerals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous to cryptocrystalline aggregates of iron and aluminum oxides/hydroxides. Individual crystals are microscopic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is a mixture of fine-grained minerals and amorphous material.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in tropical and subtropical regions with high rainfall and distinct wet and dry seasons, on stable land surfaces with good drainage, from a variety of parent rocks (e.g., basalt, granite, shale, ultramafic rocks).

Key Facts

Hardness

Variable, from 1 (soft, earthy) to 7 (hard, rock-like) on the Mohs scale, depending on induration and mineralogy. Typically 3-5 for common varieties.

Specific Gravity

Variable, typically 2.5 to 3.5, but can range from 1.8 (porous) to 4.0 (dense, iron-rich).

Crystal System

Amorphous to cryptocrystalline (not a single mineral, but a rock composed of various minerals).

Color

Reddish-brown, orange-brown, yellowish-brown, mottled.

Luster

Earthy, dull, sometimes sub-metallic.

Transparency

Opaque.

Fracture

Earthy, irregular, conchoidal in denser varieties.

Cleavage

None.

Composition

Primarily hydrated oxides of iron (goethite, hematite) and aluminum (gibbsite, boehmite, diaspore), with minor amounts of quartz, kaolinite, titanium oxides (ilmenite, anatase), and manganese oxides.

Physical characteristics

• Crystal Habit: Massive, earthy, pisolitic, nodular, vermicular, concretionary.
• Cleavage Type: Absent.
• Fracture Type: Earthy to irregular, sometimes sub-conchoidal in denser forms.
• Tenacity: Brittle when dry and indurated; friable to plastic when wet.
• Luster Type: Earthy to dull, occasionally sub-metallic.

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