How to identify Wonderstone

To correctly identify Wonderstone (Rhyolite (flow-banded)), 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

   Highly variable, often exhibiting multiple colors in distinct bands, including shades of gray, brown, red, purple, cream, and sometimes black. The banding itself is a key identifier.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to waxy or vitreous, depending on the degree of crystallinity and presence of volcanic glass.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Aphanitic (microcrystalline to cryptocrystalline) groundmass with prominent, often intricate, parallel or convoluted flow banding. Phenocrysts (larger crystals) are rare but can occur.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, with no discernible crystal forms visible to the naked eye due to its fine-grained nature. Microscopic examination reveals interlocking quartz and feldspar grains.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is a massive rock composed of interlocking grains. It exhibits fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed in volcanic settings where highly viscous, felsic (rhyolitic) lava flows. This includes continental volcanic arcs, caldera complexes, and areas of extensive silicic volcanism. It can be found in ancient volcanic terrains or more recent volcanic regions.

Key Facts

Hardness

6-7 on the Mohs scale (due to high quartz content)

Specific Gravity

2.5-2.7 g/cm³

Crystal System

Amorphous (glassy component) to microcrystalline (quartz, feldspar)

Color

Highly variable, often multi-banded (gray, brown, red, purple, cream)

Luster

Dull, waxy, or vitreous

Transparency

Opaque to translucent on thin edges

Fracture

Conchoidal to sub-conchoidal

Cleavage

None

Composition

Predominantly silica (SiO2, typically >69 wt%), with significant amounts of aluminum oxide (Al2O3), and lesser amounts of potassium oxide (K2O), sodium oxide (Na2O), iron oxides (FeO, Fe2O3), magnesium oxide (MgO), and calcium oxide (CaO).

Physical characteristics

• Crystal Habit: Massive, aphanitic, with prominent flow banding. Individual crystals are microscopic.
• Cleavage Type: Absent
• Fracture Type: Conchoidal to sub-conchoidal, producing sharp edges.
• Tenacity: Brittle
• Luster Type: Dull, waxy, or vitreous

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