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Scoria with Cinnabar is a unique geological specimen consisting of a dark, highly vesicular volcanic rock (scoria) with bright red to reddish-brown crystals or coatings of cinnabar (mercury sulfide) filling or lining its pores and fractures. The scoria provides a porous matrix, while the cinnabar stands out due to its distinctive color and often metallic to adamantine luster. The contrast between the dark, rough scoria and the vibrant cinnabar makes these specimens visually striking.
How to Identify
- Color
- Scoria is typically dark brown, black, or dark reddish-brown. Cinnabar is characterized by its distinctive vermilion red to reddish-brown color.
- Luster
- Scoria is dull to earthy. Cinnabar exhibits an adamantine to metallic luster, sometimes dull if massive.
- Texture
- 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.
- Crystal Form
- 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.
- Cleavage
- Scoria has no cleavage. Cinnabar has perfect prismatic cleavage on {1010}.
- Geological Environment
- 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)
Quick Check
- Color: Dark (scoria) with bright red to reddish-brown (cinnabar)
- Luster: Dull/earthy (scoria) with adamantine/metallic (cinnabar)
- Streak: Red (cinnabar)
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.
Formation
Scoria is a highly vesicular, dark-colored volcanic rock that forms during explosive eruptions when gas-rich magma is ejected from a volcano. The rapid cooling and depressurization cause gases to exsolve, creating numerous bubbles (vesicles) within the solidifying lava. Cinnabar (mercury sulfide, HgS) typically forms in low-temperature hydrothermal environments, often associated with volcanic activity, hot springs, and fumaroles. When cinnabar is found within scoria, it indicates that mercury-rich hydrothermal fluids have permeated the porous scoria, depositing cinnabar within its vesicles and fractures. This can occur either shortly after the scoria's formation while volcanic heat is still present, or much later as hydrothermal systems develop in the volcanic terrain.
Usage
Scoria itself is used as lightweight aggregate, in landscaping, and as a growing medium. Cinnabar is the primary ore of mercury. Historically, it was used as a pigment (vermilion) and in traditional medicine. However, due to its extreme toxicity, its use is now severely restricted. Specimens of scoria with cinnabar are primarily of scientific and collector interest.
Age Distribution
Scoria can form in geologically recent to ancient volcanic eruptions. Cinnabar deposition is typically associated with hydrothermal activity, which can occur at various geological ages, often post-dating the scoria formation or co-occurring in active volcanic-hydrothermal systems.
Where to Find
New Almaden, California, USA
Historically one of the largest mercury mines, known for cinnabar deposits often associated with volcanic and hydrothermal activity.
Almadén, Ciudad Real, Spain
Another historically significant mercury mining district, where cinnabar occurs in various geological settings, potentially including volcanic rocks.
Idrija, Slovenia
A major mercury mining area, with cinnabar found in diverse geological contexts, including those influenced by volcanic processes.
Sichuan and Guizhou Provinces, China
Significant cinnabar deposits are found here, often in association with hydrothermal alteration and volcanic rocks.
Active Volcanic-Hydrothermal Systems
Regions with ongoing volcanic activity and associated hot springs or fumaroles, such as parts of the Pacific Ring of Fire (e.g., Japan, Indonesia, New Zealand, parts of the Andes), can host such occurrences.
Finding Tips
Safety First
Cinnabar is a mercury sulfide and is highly toxic. DO NOT handle specimens without gloves. AVOID inhaling dust. DO NOT lick or ingest. Wash hands thoroughly after handling. Store in sealed containers away from children and pets. Mercury vapor can be released, especially if heated or abraded. Professional handling and storage are recommended.
Look for Volcanic Terrains
Focus on areas with recent or ancient volcanic activity, especially those known for hydrothermal alteration or hot springs.
Identify Porous Rocks
Search for scoria or other highly vesicular volcanic rocks. Cinnabar is more likely to be deposited in the open spaces of these rocks.
Observe Color and Luster
Look for bright red to reddish-brown patches or crystals with an adamantine to metallic luster within the dark, dull scoria matrix.
Check for Hydrothermal Veins
Cinnabar often occurs in veins or as coatings along fractures, so examine any cracks or fissures in volcanic rocks.
Similar Rocks
Pumice with Cinnabar
Pumice (volcanic glass) with Cinnabar (HgS)
Also known as: Cinnabar-bearing Pumice
Basalt with Cinnabar
Basalt (volcanic rock) with Cinnabar (HgS)
Also known as: Cinnabar-bearing Basalt
Rhyolite with Cinnabar
Rhyolite (volcanic rock) with Cinnabar (HgS)
Also known as: Cinnabar-bearing Rhyolite
Scientific Classification
- Mineral Class
- Sulfide (for Cinnabar)
- Group
- Sulfide minerals (for Cinnabar)
- Crystal System
- Trigonal (for Cinnabar)
- Chemical Formula
- HgS (for Cinnabar)
- Composition
- Mercury sulfide (for Cinnabar); Scoria is a mafic to intermediate volcanic rock, typically composed of volcanic glass, plagioclase, pyroxene, and sometimes olivine.
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