How to identify Red Granite

To correctly identify Red Granite (Granite (felsic intrusive igneous rock)), 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

   Predominantly red, ranging from pale pink to deep brick red, often with white, gray, or black speckles from other minerals.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to dull, depending on the mineral components and weathering.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Phaneritic (coarse-grained), meaning individual mineral crystals are visible to the naked eye and are interlocking.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Anhedral to subhedral crystals, forming an interlocking mosaic. Quartz typically anhedral, feldspars subhedral, micas euhedral to subhedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Feldspar minerals exhibit good cleavage (typically two directions at or near 90 degrees). Quartz has no cleavage. Mica has perfect basal cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in large intrusive bodies (plutons, batholiths, stocks) within continental crust, often associated with convergent plate boundaries, orogenic belts, and stable cratonic regions.

Key Facts

Hardness

6-7 on the Mohs scale (due to quartz and feldspar).

Specific Gravity

2.65-2.75 g/cm³.

Crystal System

Monoclinic (for feldspar), Hexagonal (for quartz), Monoclinic (for biotite). The rock itself is an aggregate of these minerals.

Color

Red, pink, reddish-brown, with varying amounts of white, gray, and black.

Luster

Vitreous (glassy) for quartz and feldspar, pearly for mica.

Transparency

Opaque (as a rock), individual quartz crystals can be translucent to transparent.

Fracture

Conchoidal (quartz), uneven to splintery (feldspar).

Cleavage

Good in feldspar (two directions at ~90°), perfect in mica (one basal direction), absent in quartz.

Composition

Primarily quartz (20-60%), alkali feldspar (35-90% of total feldspar), plagioclase feldspar (0-65% of total feldspar), and micas (biotite, muscovite) or amphiboles. The red color is due to iron oxides within potassium feldspar or red-stained quartz.

Physical characteristics

• Crystal Habit: Granitic (equigranular, interlocking, anhedral to subhedral crystals).
• Cleavage Type: Good in feldspar (prismatic), perfect in mica (basal).
• Fracture Type: Conchoidal (quartz), uneven to splintery (feldspar).
• Tenacity: Brittle.
• Luster Type: Vitreous to dull.

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