Blue Quartz Granite

Igneous, Plutonic

Granite with blue quartz inclusions

Also known as: Granite with blue quartz, Sodalite Granite (incorrect, but sometimes misidentified)

Got a photo? Identify rocks instantly with the Rockby app

Description

Blue Quartz Granite is an intrusive igneous rock characterized by its granitic texture and composition, with the notable presence of blue-colored quartz grains. Like other granites, it is primarily composed of quartz, feldspar (orthoclase and plagioclase), and mica (biotite and/or muscovite), along with minor accessory minerals. The blue hue of the quartz can range from a pale sky blue to a deep indigo, often appearing as distinct, sometimes translucent, grains within the otherwise typical granitic matrix of white, pink, or gray feldspars and dark micas.

How to Identify

Color: 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.
Luster: Vitreous (glassy) for quartz and feldspar, pearly to sub-vitreous for feldspar, and vitreous to silky for mica.
Texture: 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.
Crystal Form: Quartz typically anhedral to subhedral, feldspars subhedral to euhedral, micas in flaky or tabular forms.
Cleavage: Feldspars exhibit two distinct cleavages at or near 90 degrees. Micas have perfect basal cleavage. Quartz has no cleavage but exhibits conchoidal fracture.
Geological Environment: 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.

Quick Check

Color: Dominantly light-colored (white, pink, gray) with distinct blue glassy grains.
Luster: Vitreous (glassy) for quartz, pearly for feldspar, silky for mica.
Streak: White (for quartz and feldspar), colorless to pale brown (for mica).

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

Formation

Blue Quartz Granite forms from the slow crystallization of felsic magma deep within the Earth's crust. The distinctive blue color of the quartz is typically attributed to the presence of microscopic inclusions of minerals such as dumortierite, magnesioriebeckite, or ilmenite, or sometimes due to structural defects within the quartz lattice caused by radiation or titanium impurities. The slow cooling allows for the formation of large, interlocking mineral grains.

Usage

Primarily used as a decorative stone in construction (countertops, flooring, wall cladding), monuments, and occasionally for carving. Its aesthetic appeal, particularly the blue quartz, makes it desirable for architectural and ornamental purposes.

Age Distribution

Precambrian to Cenozoic, depending on the specific granite intrusion.

Where to Find

Blue Ridge Mountains, USA

Specific localities within the Appalachian Mountains, particularly in Virginia and North Carolina, are known for granites containing blue quartz, often associated with Precambrian basement rocks.

Scandinavia (e.g., Norway, Sweden)

Certain Precambrian shield areas in Scandinavia host granitic intrusions with blue quartz, sometimes referred to as 'Larvikite' (though Larvikite is technically a monzonite, some granites in the region can have blue quartz).

Brazil

Some granite quarries in Brazil produce varieties with blue quartz, often used in the dimension stone industry.

India

Certain regions in India, particularly in the southern states, have granitic occurrences with blue quartz.

Finding Tips

Look for Coarse Grains

Granite is a coarse-grained rock. Look for individual mineral crystals that are visible to the naked eye.

Identify Quartz

Quartz is typically glassy, translucent to transparent, and lacks cleavage. In Blue Quartz Granite, these grains will have a distinct blue hue.

Identify Feldspar

Feldspars are usually opaque to translucent, white, pink, or gray, and exhibit two cleavage planes at nearly 90 degrees.

Identify Mica

Mica appears as dark (biotite) or light (muscovite) flaky minerals with perfect basal cleavage.

Check for Intrusive Settings

Blue Quartz Granite is found in large igneous intrusions, often exposed in mountain ranges or eroded continental shields.

Similar Rocks

Standard Granite

Granite

Also known as: Granite

Gneiss

Also known as: Banded Gneiss

Syenite

Also known as: Nepheline Syenite

Scientific Classification

Mineral Class: Igneous Rock (Plutonic)
Group: Felsic Intrusive Rocks
Crystal System: Polycrystalline aggregate of minerals with various crystal systems (Trigonal for quartz, Monoclinic/Triclinic for feldspar, Monoclinic for mica).
Chemical Formula: Not a single chemical formula, but a mixture of SiO2 (quartz), (Na,K,Ca)(Al,Si)4O8 (feldspar), K(Mg,Fe)3AlSi3O10(OH)2 (biotite), KAl2(AlSi3O10)(OH)2 (muscovite), etc.
Composition: Silicic (felsic) rock, rich in silica (typically >68% SiO2).

Explore Blue Quartz Granite

Identification Localities & Collecting Look-alikes

Identify rocks anywhere

Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.

Download on theApp Store Get it onGoogle Play Continue onWeb

Open in app