How to identify Uranophane

To correctly identify Uranophane (Ca(UO2)2(SiO3OH)2·5H2O), 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 lemon-yellow to yellowish-green, sometimes straw-yellow or brownish-yellow. The color is often vibrant and characteristic.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Silky to vitreous, sometimes dull or earthy in massive forms.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often fibrous, acicular (needle-like), or radiating aggregates. Can also be massive, earthy, or as powdery coatings.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Monoclinic. Crystals are typically acicular to fibrous, elongated along [010], often forming radiating aggregates, tufts, or felted masses. Individual crystals are usually very small.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect on {100}, good on {001}. This can be difficult to observe due to the small crystal size and fibrous habit.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Oxidized zones of uranium ore deposits, particularly those associated with granitic or pegmatitic rocks, sandstones, or other host rocks containing primary uranium minerals. It forms as a secondary alteration product.

Key Facts

Hardness

2.5-3 on the Mohs scale

Specific Gravity

3.81-3.98 g/cm³

Crystal System

Monoclinic

Color

Lemon-yellow, yellowish-green, straw-yellow, brownish-yellow

Luster

Silky, vitreous, dull, earthy

Transparency

Transparent to translucent

Fracture

Uneven to splintery

Cleavage

Perfect on {100}, good on {001}

Composition

Hydrated Calcium Uranyl Silicate

Physical characteristics

• Crystal Habit: Acicular, fibrous, radiating aggregates, tufts, felted masses, coatings, crusts, massive, earthy, powdery.
• Cleavage Type: Perfect basal cleavage on {100}, good cleavage on {001}. Often difficult to observe due to fine-grained nature.
• Fracture Type: Uneven to splintery.
• Tenacity: Brittle.
• Luster Type: Silky to vitreous in crystalline forms; dull to earthy in massive or powdery forms.

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