How to identify Iron-stained Quartz

To correctly identify Iron-stained Quartz (SiO2 with iron oxide staining), 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

   Ranges from pale yellow, orange, and brown to deep reddish-brown or black due to iron oxide/hydroxide staining. The underlying quartz may be colorless, white, or smoky.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for the quartz, but can appear dull or earthy where the iron staining is thick or powdery.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to rough, depending on the nature and thickness of the iron staining. Quartz crystals will have characteristic smooth faces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically prismatic hexagonal crystals, massive, or granular aggregates, characteristic of quartz. The iron staining coats these forms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None (quartz). The iron staining does not affect the cleavage of the underlying quartz.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in a wide range of geological settings where quartz is present and iron-rich fluids have circulated. This includes hydrothermal veins, pegmatites, igneous rocks, metamorphic rocks, and sedimentary environments (e.g., sandstones, conglomerates).

Key Facts

Hardness

7 on the Mohs scale (for quartz). The iron staining is softer but does not significantly alter the overall hardness.

Specific Gravity

2.65 g/cm³ (for quartz). The iron staining adds negligible mass.

Crystal System

Trigonal (for quartz)

Color

Colorless, white, or smoky quartz with external or internal yellow, orange, brown, or red iron oxide/hydroxide staining.

Luster

Vitreous (glassy) to dull/earthy.

Transparency

Transparent to opaque, depending on the thickness and density of the iron staining.

Fracture

Conchoidal (for quartz).

Cleavage

None (for quartz).

Composition

Silicon dioxide (SiO2) with adsorbed or intergrown iron oxides/hydroxides (e.g., Fe2O3, FeO(OH)·nH2O).

Physical characteristics

• Crystal Habit: Prismatic hexagonal crystals, massive, granular, cryptocrystalline. The iron staining coats or permeates these forms.
• Cleavage Type: None (quartz).
• Fracture Type: Conchoidal (quartz).
• Tenacity: Brittle (quartz).
• Luster Type: Vitreous (glassy) to dull/earthy.

Explore Iron-stained Quartz