How to identify Apophyllite

To correctly identify Apophyllite (Apophyllite Group), 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

   Colorless, white, green, yellow, pink, violet. Green is particularly characteristic of some varieties.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) on crystal faces, pearly on cleavage surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, often with distinct crystal faces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Commonly forms square-pyramidal, tabular, or prismatic crystals. Often found in drusy coatings or radiating aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect basal cleavage {001}, producing pearly surfaces.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in the amygdaloidal cavities of basalt and other volcanic rocks, often associated with zeolites, calcite, and prehnite. Also in some granitic pegmatites and hydrothermal veins.

Key Facts

Hardness

4.5-5 on the Mohs scale

Specific Gravity

2.3-2.5

Crystal System

Tetragonal (for Fluorapophyllite-(K), Fluorapophyllite-(Na)) or Orthorhombic (for Hydroxyapophyllite-(K))

Color

Colorless, white, green, yellow, pink, violet

Luster

Vitreous on prism faces, pearly on basal cleavage

Transparency

Transparent to translucent

Fracture

Uneven

Cleavage

Perfect basal cleavage {001}

Composition

Hydrated potassium calcium sodium fluorosilicate

Physical characteristics

• Crystal Habit: Commonly square-pyramidal, tabular, or prismatic crystals; also massive, lamellar, or radiating aggregates. Often forms pseudo-cubic crystals.
• Cleavage Type: Perfect on {001} (basal)
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to pearly

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