How to identify Chlorite-Included Quartz with Iron Staining

To correctly identify Chlorite-Included Quartz with Iron Staining (SiO2 (Quartz) with (Mg,Fe)3(Si,Al)4O10(OH)2 (Chlorite) and Fe-oxides), 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 matrix is typically colorless, white, or smoky. Chlorite inclusions are green, dark green, or black. Iron staining is reddish-brown, orange, or yellowish-brown.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for quartz; dull to pearly for chlorite inclusions; earthy to dull for iron staining.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystalline, often with visible quartz crystal faces. Chlorite inclusions can be flaky or fibrous. Iron staining may be powdery or a thin coating.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms terminated by rhombohedra. Chlorite inclusions may be disseminated flakes, radiating aggregates, or phantom layers within the quartz. Iron oxides are typically amorphous coatings or microcrystalline aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Chlorite: Perfect basal cleavage (one direction). Iron oxides: None.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, metamorphic rocks (e.g., greenschist facies), pegmatites, and sedimentary environments where iron-rich fluids interact with quartz-bearing rocks. Often found in areas of active faulting or alteration.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Chlorite: 2-2.5. Iron oxides (e.g., goethite, hematite): 5-6.5.

Specific Gravity

Quartz: 2.65 g/cm³. Chlorite: 2.6-3.3 g/cm³. Iron oxides: 3.3-5.3 g/cm³.

Crystal System

Quartz: Trigonal. Chlorite: Monoclinic. Iron oxides: Orthorhombic (goethite), Trigonal (hematite).

Color

As described above: colorless/white/smoky quartz, green/dark green/black chlorite, reddish-brown/orange/yellowish-brown iron oxides.

Luster

Vitreous (quartz), dull to pearly (chlorite), earthy to dull (iron oxides).

Transparency

Quartz: Transparent to translucent. Chlorite: Opaque to translucent. Iron oxides: Opaque.

Fracture

Quartz: Conchoidal. Chlorite: Uneven. Iron oxides: Uneven to splintery.

Cleavage

Quartz: None. Chlorite: Perfect basal (one direction). Iron oxides: None.

Composition

Silicon dioxide (SiO2) for quartz. Hydrous magnesium iron aluminum silicate for chlorite ((Mg,Fe)3(Si,Al)4O10(OH)2). Iron oxides (e.g., FeO(OH) for goethite, Fe2O3 for hematite).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Chlorite: Flaky, platy, massive, radiating. Iron oxides: Earthy, botryoidal, massive.
• Cleavage Type: Quartz: Absent. Chlorite: Perfect in one direction {001}. Iron oxides: Absent.
• Fracture Type: Quartz: Conchoidal. Chlorite: Uneven. Iron oxides: Uneven to splintery.
• Tenacity: Quartz: Brittle. Chlorite: Flexible, inelastic. Iron oxides: Brittle.
• Luster Type: Quartz: Vitreous. Chlorite: Dull to pearly. Iron oxides: Earthy to dull.

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