How to identify Stilbite

To correctly identify Stilbite (NaCa4(Si27Al9)O72·28H2O), 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

   White, colorless, pale yellow, pink, salmon-orange, reddish-brown. Pink to salmon-orange are very characteristic.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to pearly on cleavage surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often forms radiating, sheaf-like aggregates or tabular crystals. Can also be fibrous or granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Monoclinic. Crystals are typically tabular, often forming characteristic 'sheaf-of-wheat' aggregates, divergent sprays, or bow-tie shapes. Individual crystals are often elongated along the c-axis.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect on {010}, yielding pearly luster on this surface.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Amygdaloidal cavities and fractures in basalt and other mafic volcanic rocks; hydrothermal veins; granite pegmatites; some metamorphic rocks.

Key Facts

Hardness

3.5-4 on the Mohs scale

Specific Gravity

2.12-2.22

Crystal System

Monoclinic

Color

White, colorless, pale yellow, pink, salmon-orange, reddish-brown

Luster

Vitreous to pearly

Transparency

Transparent to translucent

Fracture

Uneven

Cleavage

Perfect on {010}

Composition

Hydrous calcium sodium aluminum silicate

Physical characteristics

• Crystal Habit: Typically forms tabular crystals, often aggregated into characteristic 'sheaf-of-wheat' bundles, divergent sprays, or bow-tie shapes. Can also be fibrous, columnar, or granular.
• Cleavage Type: Perfect on one plane ({010}), leading to a pearly luster on this surface.
• Fracture Type: Uneven to subconchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy) on crystal faces, pearly on cleavage surfaces.

Explore Stilbite