How to identify Caribbean Calcite

To correctly identify Caribbean Calcite (Calcite (CaCO3) with Aragonite), 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

   Vibrant blue and green, often with white and brown banding or inclusions. The blue can range from sky blue to a deeper ocean blue, and the green can be pale to teal.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Waxy to vitreous (glassy) on fresh surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically smooth when polished, but can be slightly granular or fibrous in unpolished forms due to the aragonite component. Can feel cool to the touch.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Massive, botryoidal, or stalactitic forms are common. Individual crystals are usually microscopic within the mass, but larger calcite rhombs or aragonite needles might occasionally be visible.

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 cleavage in one direction and imperfect in two others.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, vugs, and cavities within volcanic or sedimentary rocks, where calcium-rich fluids have deposited the minerals. Often found in areas with past or present geothermal activity.

Key Facts

Hardness

3-4 on the Mohs scale (Calcite is 3, Aragonite is 3.5-4)

Specific Gravity

2.71 (Calcite) to 2.95 (Aragonite)

Crystal System

Trigonal (Calcite) and Orthorhombic (Aragonite)

Color

Blue, green, white, brown

Luster

Waxy to vitreous

Transparency

Opaque to translucent

Fracture

Conchoidal to uneven

Cleavage

Perfect rhombohedral (Calcite); Distinct to imperfect (Aragonite)

Composition

Calcium Carbonate (CaCO3)

Physical characteristics

• Crystal Habit: Massive, granular, fibrous, botryoidal, stalactitic. Individual crystals are typically microscopic within the aggregate.
• Cleavage Type: Calcite: Perfect rhombohedral in three directions at 74°55'. Aragonite: Distinct {010}, imperfect {110} and {011}.
• Fracture Type: Conchoidal to uneven, splintery in some aragonite forms.
• Tenacity: Brittle
• Luster Type: Waxy to vitreous

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