How to identify Iron-stained Quartzite

To correctly identify Iron-stained Quartzite (Quartzite (metamorphic rock, primarily 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

   Typically yellow, orange, brown, red, or purplish due to iron oxide staining. Can also be white, gray, or pink if iron staining is minimal or absent.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to greasy on freshly broken surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granular, sugary, or massive. Individual quartz grains are typically interlocked and not easily discernible without magnification. Non-foliated.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Anhedral, interlocking quartz grains. Original detrital grain shapes are usually obliterated by recrystallization.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None (quartz itself lacks cleavage). The rock breaks by fracture across the grains.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed in regions subjected to regional metamorphism (e.g., mountain belts, cratonic interiors) or contact metamorphism (adjacent to igneous intrusions) where quartz-rich sandstones were present. Often found in ancient shield areas, fold-and-thrust belts, and areas of significant crustal thickening.

Key Facts

Hardness

7 (Mohs scale) for quartz, making the rock very hard.

Specific Gravity

2.65 - 2.70 g/cm³ (for pure quartz; slightly higher if significant iron oxides are present).

Crystal System

Trigonal (for quartz). The rock itself is a massive aggregate of anhedral crystals.

Color

Variable, predominantly yellow, orange, brown, red, purplish due to iron oxide staining. Can also be white, gray, or pink.

Luster

Vitreous (glassy) to greasy on fresh surfaces.

Transparency

Opaque to translucent in thin sections; individual quartz grains can be transparent.

Fracture

Conchoidal to subconchoidal, splintery, or irregular.

Cleavage

None (for quartz).

Composition

Primarily silicon dioxide (SiO2) in the form of quartz, with varying amounts of iron oxides (e.g., Fe2O3, FeO(OH)·nH2O) as staining agents. Minor accessory minerals may include feldspar, mica, zircon, rutile, magnetite, and tourmaline.

Physical characteristics

• Crystal Habit: Massive, granular, interlocking anhedral quartz grains.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal to subconchoidal, splintery, or irregular.
• Tenacity: Brittle.
• Luster Type: Vitreous to greasy.

Explore Iron-stained Quartzite