How to identify Iron-Stained Quartz

To correctly identify Iron-Stained Quartz (SiO2 (Quartz) with Fe-oxides/hydroxides), 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, reddish-brown, to dark brown. The color is typically unevenly distributed, often concentrated in fractures or on crystal faces, distinguishing it from uniformly colored quartz varieties.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for the quartz, often duller or earthy where iron oxides form a thick coating.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to rough, depending on the extent and nature of the iron staining. Quartz itself is typically smooth.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal prisms with pyramidal terminations (for macrocrystalline quartz), or massive/botryoidal (for chalcedony/cryptocrystalline quartz). The iron staining often highlights these forms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None (quartz). The iron oxides/hydroxides do not impart cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Common in weathered zones of ore deposits, hydrothermal veins, sedimentary environments (e.g., sandstones, conglomerates), and metamorphic rocks where iron-bearing minerals have been altered.

Key Facts

Hardness

7 (Mohs scale) for quartz; iron oxides/hydroxides are softer (e.g., hematite 5-6, goethite 5-5.5)

Specific Gravity

2.65 g/cm³ (quartz); iron oxides/hydroxides are denser (e.g., hematite 5.26, goethite 3.3-4.3)

Crystal System

Trigonal (quartz); iron oxides/hydroxides vary (e.g., hematite trigonal, goethite orthorhombic)

Color

Colorless to white (quartz) with yellow, orange, red, or brown staining from iron oxides/hydroxides.

Luster

Vitreous (quartz), earthy to submetallic (iron oxides/hydroxides)

Transparency

Transparent to opaque (quartz), opaque (iron oxides/hydroxides)

Fracture

Conchoidal (quartz)

Cleavage

None (quartz)

Composition

SiO2 (Quartz) with Fe2O3 (Hematite), FeO(OH)·nH2O (Goethite/Limonite)

Physical characteristics

• Crystal Habit: Prismatic, massive, granular, cryptocrystalline. Iron staining often coats or fills interstices.
• Cleavage Type: Absent (quartz)
• Fracture Type: Conchoidal (quartz)
• Tenacity: Brittle (quartz)
• Luster Type: Vitreous (quartz), earthy to submetallic (iron oxides/hydroxides)

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