How to identify Celestite

To correctly identify Celestite (SrSO4), 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 sky-blue, but can also be colorless, white, pale yellow, or reddish-brown.

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 tabular or prismatic crystals, sometimes radiating or fibrous aggregates. Can also be massive or granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Orthorhombic system, typically forming tabular crystals parallel to {001}, prismatic crystals elongated along the a- or b-axis, or equant crystals. Often found as drusy coatings or in geodes.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect cleavage parallel to {001}, good cleavage parallel to {210}, and imperfect cleavage parallel to {100}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Most commonly found in sedimentary rocks, particularly limestones, dolomites, and shales, often as concretions or geodes. Also occurs in evaporite deposits, hydrothermal veins, and as a gangue mineral in some ore deposits.

Key Facts

Hardness

3-3.5 on the Mohs scale

Specific Gravity

3.9-4.0

Crystal System

Orthorhombic

Color

Typically sky-blue, but can be colorless, white, pale yellow, or reddish-brown.

Luster

Vitreous to pearly

Transparency

Transparent to translucent

Fracture

Uneven to conchoidal

Cleavage

Perfect on {001}, good on {210}, imperfect on {100}

Composition

Strontium sulfate (SrSO4)

Physical characteristics

• Crystal Habit: Tabular, prismatic, fibrous, granular, massive, often in geodes or as radiating aggregates.
• Cleavage Type: Perfect basal cleavage, good prismatic cleavage, imperfect pinacoidal cleavage.
• Fracture Type: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to pearly.

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