How to identify Larimar

To correctly identify Larimar (Pectolite (blue variety)), 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

   Ranges from light blue to sky blue, often with white, gray, or reddish-brown streaks and patterns. The blue color can be intense, resembling the Caribbean Sea.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to silky when polished, dull to sub-vitreous in rough form.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically massive, with a fine-grained, fibrous texture that is often visible on broken surfaces. Can appear somewhat translucent to opaque.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Massive, compact, and fibrous aggregates. Individual crystals are acicular (needle-like) but rarely visible to the naked eye in Larimar.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect on {100} and {001}, but rarely observed in massive Larimar specimens.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found exclusively in basaltic volcanic rocks, specifically in amygdaloidal cavities and fractures within highly altered basaltic andesite and basalt. It is a product of hydrothermal alteration.

Key Facts

Hardness

4.5-5 on the Mohs scale

Specific Gravity

2.74-2.88

Crystal System

Triclinic

Color

Light blue to sky blue, blue-green, often with white, gray, or reddish-brown patterns.

Luster

Vitreous to silky

Transparency

Translucent to opaque

Fracture

Uneven to splintery

Cleavage

Perfect on {100} and {001}

Composition

Hydrous sodium calcium silicate

Physical characteristics

• Crystal Habit: Massive, compact, fibrous aggregates; individual crystals are acicular (needle-like) but microscopic.
• Cleavage Type: Perfect in two directions, {100} and {001}, at nearly 90 degrees.
• Fracture Type: Uneven to splintery, due to its fibrous nature.
• Tenacity: Brittle
• Luster Type: Vitreous to silky, especially on polished surfaces.

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