How to identify Scoria with Cinnabar

To correctly identify Scoria with Cinnabar (Scoria (volcanic rock) with Cinnabar (HgS)), 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

   Scoria is typically dark brown, black, or dark reddish-brown. Cinnabar is characterized by its distinctive vermilion red to reddish-brown color.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Scoria is dull to earthy. Cinnabar exhibits an adamantine to metallic luster, sometimes dull if massive.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Scoria is highly vesicular, rough, and often frothy, with numerous gas bubbles. Cinnabar will appear as crystalline coatings, masses, or individual crystals within the vesicles or fractures of the scoria.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Scoria is amorphous or microcrystalline. Cinnabar typically forms as trigonal crystals, often as rhombohedra, or as granular to massive aggregates. In scoria, it's commonly found as small, euhedral to subhedral crystals or as fine-grained coatings.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Scoria has no cleavage. Cinnabar has perfect prismatic cleavage on {1010}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in volcanic regions, particularly in areas with active or past hydrothermal systems, hot springs, and fumaroles, where mercury-rich fluids have interacted with porous volcanic rocks.

Key Facts

Hardness

Scoria: Varies, typically 5-6 (Mohs) for the mineral components, but the rock is brittle. Cinnabar: 2-2.5 (Mohs)

Specific Gravity

Scoria: 1.0-2.0 g/cm³ (due to high porosity, it can float). Cinnabar: 8.1 g/cm³ (very high)

Crystal System

Scoria: Amorphous to microcrystalline. Cinnabar: Trigonal

Color

Scoria: Black, dark brown, dark reddish-brown. Cinnabar: Vermilion red, reddish-brown

Luster

Scoria: Dull, earthy. Cinnabar: Adamantine to metallic, sometimes dull

Transparency

Scoria: Opaque. Cinnabar: Transparent to opaque

Fracture

Scoria: Conchoidal to irregular. Cinnabar: Uneven to subconchoidal

Cleavage

Scoria: None. Cinnabar: Perfect prismatic on {1010}

Composition

Scoria: Primarily basaltic or andesitic glass and microlites (plagioclase, pyroxene, olivine). Cinnabar: Mercury sulfide (HgS)

Physical characteristics

• Crystal Habit: Scoria: Amorphous, vesicular. Cinnabar: Rhombohedral crystals, granular, massive, earthy coatings within vesicles and fractures.
• Cleavage Type: Scoria: Not applicable. Cinnabar: Perfect prismatic {1010}.
• Fracture Type: Scoria: Conchoidal to irregular. Cinnabar: Uneven to subconchoidal.
• Tenacity: Scoria: Brittle. Cinnabar: Brittle.
• Luster Type: Scoria: Dull, earthy. Cinnabar: Adamantine to metallic.

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