Quartz and Granite

Igneous Rock (Granite), Mineral (Quartz)

SiO2 (Quartz), Igneous rock (Granite)

Also known as: Granite (for the rock), Silica (for Quartz)

Got a photo? Identify rocks instantly with the Rockby app

Description

Granite is a coarse-grained, felsic intrusive igneous rock. It is typically light-colored, ranging from white to pink to gray, depending on its mineralogy. Its defining characteristic is its interlocking crystalline texture, with visible grains of quartz, feldspar, and mica. Quartz is a hard, crystalline mineral composed of silicon and oxygen atoms (SiO2). It is one of the most abundant minerals in Earth's continental crust. In granite, quartz appears as glassy, often anhedral (irregularly shaped) grains filling the spaces between other minerals, or sometimes as subhedral to euhedral crystals.

How to Identify

Color: Granite: Typically light-colored (white, gray, pink, red). Quartz: Colorless, white, purple (amethyst), yellow (citrine), brown (smoky quartz), pink (rose quartz), green (prasiolite), black (morion).
Luster: Granite: Overall dull to vitreous due to constituent minerals. Quartz: Vitreous (glassy) to greasy.
Texture: Granite: Phaneritic (coarse-grained), interlocking crystalline texture. Quartz: Crystalline, often anhedral in granite, but can form euhedral hexagonal prisms with pyramidal terminations in vugs or veins.
Crystal Form: Granite: Granular, interlocking crystals of quartz, feldspar, and mica. Quartz: Hexagonal prisms with pyramidal terminations (when euhedral), massive, granular.
Cleavage: Granite: No overall cleavage, but constituent minerals like feldspar and mica exhibit cleavage. Quartz: None (conchoidal fracture).
Geological Environment: Granite: Intrusive igneous bodies (batholiths, stocks, dikes, sills) in continental crust, often associated with orogenic belts. Quartz: Ubiquitous in igneous, metamorphic, and sedimentary rocks; hydrothermal veins, pegmatites, sandstones, quartzites.

Key Facts

Hardness: Granite: 6-7 (overall, due to constituent minerals). Quartz: 7 (Mohs scale).
Specific Gravity: Granite: 2.65-2.75 g/cm³. Quartz: 2.65 g/cm³.
Crystal System: Granite: Not applicable (rock). Quartz: Trigonal.
Color: Granite: White, gray, pink, red. Quartz: Colorless, white, purple, yellow, brown, pink, green, black.
Luster: Granite: Vitreous to dull. Quartz: Vitreous to greasy.
Transparency: Granite: Opaque. Quartz: Transparent to translucent.
Fracture: Granite: Irregular to conchoidal (within quartz grains). Quartz: Conchoidal.
Cleavage: Granite: None (as a rock), but constituent feldspar has good cleavage. Quartz: None.
Composition: Granite: Primarily quartz, feldspar (orthoclase, plagioclase), mica (biotite, muscovite). Quartz: Silicon dioxide (SiO2).

Quick Check

Color: Granite: Light (white, gray, pink). Quartz: Variable, often colorless/white.
Luster: Granite: Dull to vitreous. Quartz: Vitreous.
Streak: Granite: White (due to feldspar and quartz). Quartz: White.

Physical Characteristics

Crystal Habit: Granite: Granular, massive. Quartz: Prismatic, massive, granular, cryptocrystalline (e.g., chalcedony).
Cleavage Type: Granite: Not applicable (rock). Quartz: Absent.
Fracture Type: Granite: Irregular to subconchoidal. Quartz: Conchoidal.
Tenacity: Granite: Brittle. Quartz: Brittle.
Luster Type: Granite: Vitreous to dull. Quartz: Vitreous to greasy.

Formation

Granite is an intrusive igneous rock that forms from the slow crystallization of magma beneath Earth's surface. It is primarily composed of quartz, feldspar (orthoclase and plagioclase), and mica (biotite and/or muscovite), along with minor accessory minerals. Quartz, as a mineral, forms under a wide range of temperatures and pressures in igneous, metamorphic, and sedimentary environments. In granite, quartz crystallizes from the cooling magma.

Usage

Granite is widely used as a construction material (countertops, flooring, building facades), monumental stone, and for paving. Quartz is used in electronics (oscillators, filters), optics, abrasives, glass manufacturing, and as a gemstone. Both are fundamental components of many industrial processes.

Age Distribution

Granite formation has occurred throughout Earth's history, from the Archean Eon to the Cenozoic Era. Quartz is ubiquitous in crustal rocks of all ages.

Where to Find

Sierra Nevada Batholith, USA

A vast granitic intrusion forming the core of the Sierra Nevada mountain range in California, USA.

Appalachian Mountains, USA

Numerous granite intrusions and metamorphic rocks containing abundant quartz are found throughout the Appalachian Orogen.

Fennoscandian Shield, Europe

Extensive areas of ancient granitic and gneissic rocks, rich in quartz, are found across Scandinavia and Finland.

Brazilian Shield, South America

Large exposures of Precambrian granites and quartz-rich metamorphic rocks.

Western Australia

Significant granite-greenstone terrains and quartz-rich sedimentary basins.

Finding Tips

Look for outcrops in mountainous regions

Granite often forms large, resistant outcrops in areas of uplift and erosion.

Examine riverbeds and glacial deposits

Granite and quartz are resistant to weathering and are commonly found as pebbles and cobbles in these environments.

Identify characteristic mineral grains

Look for the glassy, irregular grains of quartz, the blocky feldspars, and the flaky micas to identify granite. For individual quartz crystals, look for hexagonal prisms.

Check for hardness

Quartz is harder than most common minerals (Mohs 7), so it will scratch glass and steel. This is a good field test for quartz within granite or as a standalone mineral.

Similar Rocks

Diorite

Also known as: Black Granite (misnomer)

Gabbro

Also known as: Black Granite (misnomer)

Rhyolite

Also known as: Volcanic Granite

Gneiss

Also known as: Banded Granite

Scientific Classification

Mineral Class: Granite: Igneous Rock. Quartz: Silicate mineral (Tectosilicate subclass).
Group: Granite: Felsic intrusive igneous rock. Quartz: Quartz group.
Crystal System: Granite: Not applicable (polycrystalline aggregate). Quartz: Trigonal.
Chemical Formula: Granite: Variable (complex silicate mixture). Quartz: SiO2.
Composition: Granite: SiO2 (65-75%), Al2O3, K2O, Na2O, CaO, FeO, MgO. Quartz: 46.7% Silicon, 53.3% Oxygen.

Explore Quartz and 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