How to identify Larimar

To correctly identify Larimar (Pectolite (a variety of)), 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 sky blue to deep blue, often with white, light blue, or sometimes reddish-brown streaks and patterns. The blue color is due to copper.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Silky to vitreous when polished; dull to sub-vitreous in rough form.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fibrous, often appearing as radiating aggregates or dense masses. Can feel smooth and cool to the touch when polished.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically occurs as massive, compact, or fibrous aggregates within vugs and fractures in volcanic rock. Individual crystals are acicular (needle-like) but rarely visible to the naked eye.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect cleavage in one direction ({100}), which can make it somewhat fragile and prone to splintering if struck along the cleavage plane.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found exclusively in highly altered basaltic andesite and basaltic rocks, specifically in the amygdaloidal cavities and fractures within these volcanic formations. Its formation is associated with hydrothermal activity.

Key Facts

Hardness

4.5-5 on the Mohs scale.

Specific Gravity

2.74-2.88.

Crystal System

Triclinic.

Color

Blue, blue-green, often with white mottling.

Luster

Silky to vitreous.

Transparency

Translucent to opaque.

Fracture

Uneven to splintery.

Cleavage

Perfect on {100}.

Composition

Sodium calcium inosilicate hydrate, with copper impurities causing the blue color. NaCa2Si3O8(OH).

Physical characteristics

• Crystal Habit: Typically massive, compact, or fibrous aggregates; individual crystals are acicular (needle-like) but microscopic.
• Cleavage Type: Perfect in one direction ({100}), leading to a tendency to splinter along this plane.
• Fracture Type: Uneven to splintery, reflecting its fibrous nature.
• Tenacity: Brittle.
• Luster Type: Silky to vitreous (glassy) when polished; dull to sub-vitreous in rough form.

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