How to identify Aragonite

To correctly identify Aragonite (Aragonite (CaCO3)), 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 white, colorless, or gray. Can also be yellow, green, blue, violet, or brown due to impurities.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be fibrous, columnar, granular, or massive. Often forms radiating aggregates or acicular crystals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Orthorhombic system. Commonly forms prismatic, acicular, or tabular crystals. Also found in botryoidal, stalactitic, and coralloidal (e.g., 'Flos Ferri') habits. Twinning is common, often forming pseudo-hexagonal prisms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Distinct cleavage in one direction ({010}), poor in two others ({110} and {011}). Often difficult to observe due to fibrous or fine-grained habits.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in sedimentary environments (e.g., marine and freshwater precipitates, ooids, shells), hydrothermal veins, hot springs, caves (speleothems), serpentinites, and as a component of some igneous rocks (e.g., carbonatites).

Key Facts

Hardness

3.5-4 (Mohs scale)

Specific Gravity

2.93-2.95 g/cm³

Crystal System

Orthorhombic

Color

White, colorless, gray, yellow, green, blue, violet, brown

Luster

Vitreous to resinous

Transparency

Transparent to translucent

Fracture

Subconchoidal to uneven

Cleavage

Distinct on {010}, poor on {110} and {011}

Composition

Calcium Carbonate (CaCO3)

Physical characteristics

• Crystal Habit: Prismatic, acicular, tabular, fibrous, columnar, radiating, botryoidal, stalactitic, coralloidal (Flos Ferri). Often twinned, forming pseudo-hexagonal prisms.
• Cleavage Type: Distinct in one direction ({010}), poor in two others ({110} and {011}).
• Fracture Type: Subconchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy) to resinous.

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