How to identify Blue Quartz Granite

To correctly identify Blue Quartz Granite (Granite with blue quartz inclusions), 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

   Overall color varies depending on the feldspar and mica content, but the defining feature is the presence of distinct blue quartz grains. The matrix can be white, pink, gray, or reddish.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for quartz and feldspar, pearly to sub-vitreous for feldspar, and vitreous to silky for mica.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Phaneritic (coarse-grained), interlocking crystalline texture, characteristic of plutonic igneous rocks. Grains are typically visible to the naked eye, ranging from a few millimeters to several centimeters.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically anhedral to subhedral, feldspars subhedral to euhedral, micas in flaky or tabular forms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Feldspars exhibit two distinct cleavages at or near 90 degrees. Micas have perfect basal cleavage. Quartz has no cleavage but exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in large intrusive bodies (batholiths, stocks, dikes) within continental crust, often associated with orogenic belts and subduction zones where felsic magma is generated and emplaced at depth.

Key Facts

Hardness

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

Specific Gravity

2.6-2.8 g/cm³

Crystal System

Quartz: Trigonal; Feldspar: Monoclinic/Triclinic; Mica: Monoclinic

Color

Variable matrix (white, pink, gray) with blue quartz grains.

Luster

Vitreous to sub-vitreous (quartz, feldspar), pearly (feldspar), vitreous to silky (mica).

Transparency

Opaque to translucent (feldspar, mica), translucent to transparent (quartz).

Fracture

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

Cleavage

Feldspar: 2 directions at ~90°; Mica: 1 perfect basal direction; Quartz: None.

Composition

Primarily quartz (20-60%), alkali feldspar (35-60%), plagioclase feldspar (0-35%), and micas (biotite, muscovite) (5-20%). Accessory minerals may include hornblende, zircon, apatite, magnetite, ilmenite, and dumortierite.

Physical characteristics

• Crystal Habit: Granular, anhedral to subhedral interlocking crystals.
• Cleavage Type: Good in feldspars (two directions), perfect in micas (one direction), absent in quartz.
• Fracture Type: Conchoidal in quartz, uneven to splintery in other minerals.
• Tenacity: Brittle
• Luster Type: Vitreous to sub-vitreous

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