How to identify Quartz with Cinnabar

To correctly identify Quartz with Cinnabar (SiO2 with 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

   Quartz can be colorless, white, milky, smoky, or amethystine. Cinnabar is typically vermilion red, reddish-brown, or scarlet. The combination presents a striking red against a lighter background.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz has a vitreous (glassy) luster. Cinnabar has an adamantine (diamond-like) to sub-metallic luster, sometimes dull in massive forms.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Quartz can be crystalline (euhedral to anhedral crystals), massive, or cryptocrystalline (chalcedony). Cinnabar can be granular, massive, or as distinct rhombohedral or tabular crystals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms terminated by rhombohedra. Cinnabar forms trigonal crystals, often as rhombohedra, tabular, or prismatic forms, but is frequently massive or granular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Cinnabar has perfect prismatic cleavage on {1010}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Low-temperature hydrothermal veins, hot spring deposits, and volcanic environments, often associated with fault zones and areas of active or recent volcanism.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Cinnabar: 2-2.5 on Mohs scale.

Specific Gravity

Quartz: 2.65 g/cm³. Cinnabar: 8.0-8.2 g/cm³ (very dense).

Crystal System

Quartz: Trigonal. Cinnabar: Trigonal.

Color

Quartz: Colorless, white, milky, smoky, purple. Cinnabar: Vermilion red, reddish-brown, scarlet.

Luster

Quartz: Vitreous. Cinnabar: Adamantine to sub-metallic, sometimes dull.

Transparency

Quartz: Transparent to translucent. Cinnabar: Opaque to translucent.

Fracture

Quartz: Conchoidal. Cinnabar: Uneven to sub-conchoidal.

Cleavage

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

Composition

Quartz: Silicon dioxide (SiO2). Cinnabar: Mercury sulfide (HgS).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular, cryptocrystalline. Cinnabar: Rhombohedral, tabular, prismatic, massive, granular, earthy coatings.
• Cleavage Type: Quartz: Absent. Cinnabar: Perfect prismatic.
• Fracture Type: Quartz: Conchoidal. Cinnabar: Uneven to sub-conchoidal.
• Tenacity: Quartz: Brittle. Cinnabar: Brittle.
• Luster Type: Quartz: Vitreous. Cinnabar: Adamantine to sub-metallic.

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