How to identify Blue Chalcedony

To correctly identify Blue Chalcedony (Chalcedony (a cryptocrystalline variety of Quartz)), 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

   Ranges from pale sky blue to grayish-blue, sometimes with a milky or cloudy appearance. Can be uniform or exhibit subtle banding (e.g., Blue Lace Agate).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Waxy to dull, sometimes vitreous on fractured surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly granular, often exhibiting botryoidal or mammillary forms when found in cavities.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cryptocrystalline, meaning individual crystals are microscopic. Macroscopically, it forms massive, botryoidal, mammillary, or stalactitic aggregates. It does not exhibit macroscopic crystal faces.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Exhibits a conchoidal to uneven fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in amygdaloidal cavities and veins within volcanic rocks (basalts, andesites, rhyolites), and sometimes in sedimentary rocks (limestones, sandstones) where silica-rich fluids have permeated and deposited.

Key Facts

Hardness

6.5 - 7 on the Mohs scale

Specific Gravity

2.55 - 2.65

Crystal System

Trigonal (cryptocrystalline aggregates of quartz)

Color

Pale to deep blue, grayish-blue, often milky or cloudy.

Luster

Waxy to dull, sometimes vitreous.

Transparency

Translucent to opaque.

Fracture

Conchoidal to uneven.

Cleavage

None.

Composition

Silicon dioxide (SiO2).

Physical characteristics

• Crystal Habit: Cryptocrystalline aggregates, massive, botryoidal, mammillary, stalactitic, reniform.
• Cleavage Type: None.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Waxy to dull, sometimes vitreous.

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