How to identify Caribbean Calcite

To correctly identify Caribbean Calcite (Calcite (CaCO3) with 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

   Dominantly light blue to blue-green, often with white, cream, or light brown banding or inclusions. The blue is characteristic of the calcite component, while the white/brown is typically aragonite.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to resinous on fresh surfaces, dull to earthy on unpolished or weathered surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often exhibits a banded or layered texture due to the intergrowth of calcite and aragonite. Can be massive, botryoidal, or stalactitic. Polished surfaces are smooth.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Calcite typically forms massive, granular, or rhombohedral crystals. Aragonite often forms acicular (needle-like), fibrous, or botryoidal (grape-like) aggregates. In Caribbean Calcite, these forms are intergrown.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Calcite exhibits perfect rhombohedral cleavage in three directions, producing characteristic rhomb-shaped fragments. Aragonite has distinct prismatic cleavage, but it is less commonly observed in massive aggregates.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in hydrothermal veins, karstic cave formations (speleothems), or as precipitates in hot springs. The specific environment for Caribbean Calcite suggests hydrothermal alteration within volcanic or sedimentary host rocks.

Key Facts

Hardness

Calcite: 3 on Mohs scale; Aragonite: 3.5-4 on Mohs scale. The aggregate will have an average hardness within this range.

Specific Gravity

Calcite: 2.71 g/cm³; Aragonite: 2.93-2.95 g/cm³. The aggregate will fall between these values, typically around 2.7-2.9 g/cm³.

Crystal System

Calcite: Trigonal; Aragonite: Orthorhombic. Caribbean Calcite is an aggregate of both.

Color

Light blue to blue-green, often with white, cream, or light brown banding.

Luster

Vitreous to resinous.

Transparency

Translucent to opaque.

Fracture

Calcite: Conchoidal to uneven; Aragonite: Subconchoidal.

Cleavage

Calcite: Perfect rhombohedral in three directions; Aragonite: Distinct prismatic.

Composition

Calcium Carbonate (CaCO3) in two different polymorphs.

Physical characteristics

• Crystal Habit: Massive, granular, botryoidal, fibrous, stalactitic, often intergrown.
• Cleavage Type: Calcite: Rhombohedral; Aragonite: Prismatic.
• Fracture Type: Conchoidal to uneven (calcite), subconchoidal (aragonite).
• Tenacity: Brittle.
• Luster Type: Vitreous to resinous.

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