How to identify Okenite

To correctly identify Okenite (Ca10Si18O46·18H2O), 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

   Typically white, sometimes with a very faint yellowish or grayish tint.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Silky to pearly when individual fibers are visible; aggregate masses appear dull to silky.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Extremely soft and fibrous, often described as feeling like cotton or wool. The aggregates are very delicate and easily crushed.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Usually found as spherical or hemispherical aggregates of radiating acicular (needle-like) crystals, often referred to as 'cotton balls' or 'snowballs'. Individual crystals are monoclinic but rarely seen distinctly.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect on {100} and {001}, but rarely observed due to the fibrous habit and extreme fragility.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Occurs as a secondary mineral in amygdaloidal cavities and geodes within basaltic and other volcanic rocks, formed by low-temperature hydrothermal alteration. It is commonly associated with zeolites (e.g., apophyllite, stilbite, heulandite), prehnite, and calcite.

Key Facts

Hardness

1 on the Mohs scale (extremely soft)

Specific Gravity

2.33 - 2.36 g/cm³

Crystal System

Triclinic (often described as monoclinic in older literature, but modern analysis confirms triclinic)

Color

White, sometimes with a faint yellowish or grayish tint

Luster

Silky to pearly

Transparency

Translucent to opaque

Fracture

Uneven, but rarely observed due to fibrous nature

Cleavage

Perfect on {100} and {001}, but rarely seen due to fibrous habit

Composition

Hydrous Calcium Silicate

Physical characteristics

• Crystal Habit: Typically forms spherical or hemispherical aggregates of radiating acicular (needle-like) crystals, resembling cotton balls or snowballs. Individual crystals are rarely distinct.
• Cleavage Type: Perfect in two directions ({100} and {001}), but difficult to observe due to the fibrous nature and extreme softness.
• Fracture Type: Uneven, but not typically observed due to the mineral's fibrous and fragile nature.
• Tenacity: Brittle, but more accurately described as extremely fragile and easily crushed due to its delicate fibrous structure.
• Luster Type: Silky to pearly on individual fibers; aggregate masses appear dull to silky.

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