How to identify Iron-Stained Quartz

To correctly identify Iron-Stained Quartz (SiO2 (Quartz) with 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

   Typically yellow, orange, red, or brown, often unevenly distributed as a coating or within fractures. The underlying quartz may be clear, white, or milky.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for the quartz, but the iron staining can impart a duller, earthy, or sub-metallic luster in heavily coated areas.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to rough, depending on the thickness and nature of the iron oxide coating. Quartz itself is typically smooth.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Can occur as well-formed hexagonal prisms with pyramidal terminations (if the quartz is crystalline) or as massive, anhedral aggregates. The iron staining conforms to the quartz's existing form.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

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

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Common in weathered igneous, metamorphic, and sedimentary rocks; hydrothermal veins; and alluvial deposits. Any environment where quartz is present and exposed to iron-rich, oxidizing fluids.

Key Facts

Hardness

7 on Mohs scale (for quartz)

Specific Gravity

2.65 g/cm³ (for quartz)

Crystal System

Trigonal (for quartz)

Color

Colorless, white, or milky for the quartz, with yellow, orange, red, or brown staining.

Luster

Vitreous (glassy) for quartz; earthy to dull for iron oxide coatings.

Transparency

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

Fracture

Conchoidal (for quartz)

Cleavage

None (for quartz)

Composition

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

Physical characteristics

• Crystal Habit: Prismatic, massive, granular, cryptocrystalline. Iron staining coats these forms.
• Cleavage Type: Absent
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to earthy

Explore Iron-Stained Quartz