Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
A quartz vein in metamorphic rock is a geological structure characterized by a tabular or sheet-like body of quartz (SiO2) that has precipitated from hydrothermal fluids within fractures or fissures in a metamorphic host rock. The veins can range in thickness from hairline fractures to several meters wide and can extend for considerable distances. The quartz within the vein is typically massive, crystalline, or sometimes forms euhedral crystals (e.g., rock crystal, amethyst, citrine) if open spaces were available during growth. The contact between the quartz vein and the metamorphic host rock can be sharp or gradational, sometimes showing alteration halos in the surrounding rock. The metamorphic host rock itself can be of various types, such as schist, gneiss, slate, phyllite, or quartzite, and its texture and mineralogy will reflect its metamorphic history.
How to Identify
- Color
- Typically white to milky white, but can be clear (rock crystal), purple (amethyst), yellow (citrine), smoky gray (smoky quartz), or other colors due to impurities or irradiation. The host metamorphic rock will have its own characteristic color.
- Luster
- Vitreous (glassy) to greasy on fresh surfaces.
- Texture
- The quartz within the vein is typically massive, granular, or crystalline. It can be fine-grained to coarse-grained. The host metamorphic rock will exhibit textures characteristic of metamorphism, such as foliation (schistosity, gneissic banding) or granoblastic textures.
- Crystal Form
- Quartz often forms anhedral (irregular) masses filling fractures. If open space was available, it can form euhedral to subhedral hexagonal prisms with pyramidal terminations. In veins, it often forms interlocking anhedral grains.
- Cleavage
- None. Quartz exhibits conchoidal fracture.
- Geological Environment
- Common in regions that have undergone regional or contact metamorphism, particularly in areas with significant faulting, fracturing, and hydrothermal activity. Often associated with orogenic belts, subduction zones, and areas of crustal extension or compression where fluid flow is active.
Key Facts
- Hardness: 7 on the Mohs scale.
- Specific Gravity: 2.65 g/cm³.
- Crystal System: Trigonal (or hexagonal, depending on convention).
- Color: Colorless, white, milky, purple, pink, brown, black, yellow, green, blue.
- Luster: Vitreous to greasy.
- Transparency: Transparent to opaque.
- Fracture: Conchoidal.
- Cleavage: None.
- Composition: Silicon dioxide (SiO2).
Quick Check
- Color: White, milky, clear, or various colors due to impurities.
- Luster: Vitreous to greasy.
- Streak: White.
Physical Characteristics
- Crystal Habit: Massive, granular, crystalline (prismatic, pyramidal if euhedral).
- Cleavage Type: Absent.
- Fracture Type: Conchoidal.
- Tenacity: Brittle.
- Luster Type: Vitreous (glassy) to greasy.
Formation
Quartz veins in metamorphic rocks form primarily through hydrothermal processes. During metamorphism, fluids (often rich in dissolved silica) are generated or mobilized within the crust. These fluids migrate through fractures, faults, and other zones of weakness in the metamorphic host rock. As the fluids cool, or as pressure and chemical conditions change, dissolved silica precipitates to form quartz, filling these open spaces. The source of silica can be from the host rock itself (e.g., dissolution of silicates) or from external magmatic or deep crustal sources. Vein formation can be synchronous with or post-date the main metamorphic events.
Usage
Quartz veins are significant economically as they can host valuable ore deposits, particularly gold (Au), silver (Ag), and various base metals (e.g., copper, lead, zinc). The quartz itself, if pure and in sufficient quantity, can be used as a source of industrial silica for glassmaking, ceramics, abrasives, and electronics. Historically, quartz veins were often prospected for their potential to contain precious metals. In some cases, large, clear quartz crystals from veins are used as gemstones or for ornamental purposes.
Age Distribution
Can form in metamorphic rocks of any age, from Precambrian to Cenozoic, depending on the timing of metamorphic and hydrothermal events.
Where to Find
Canadian Shield, Canada
Extensive Precambrian metamorphic terrains with numerous gold-bearing quartz veins.
Appalachian Mountains, USA
Paleozoic metamorphic belts with widespread quartz veining, some historically mined for gold.
Western Cordillera, USA (e.g., Sierra Nevada)
Mesozoic metamorphic rocks associated with magmatic arcs, hosting significant gold-quartz vein deposits.
European Alps
Alpine orogenic belt with various metamorphic rocks and associated quartz veins, sometimes containing well-formed quartz crystals.
Kalgoorlie, Western Australia
Famous for its Archean greenstone belts and associated gold-rich quartz veins.
Finding Tips
Look for Linear Features
Quartz veins often appear as linear, lighter-colored bands cutting across darker metamorphic host rocks. They can be exposed in road cuts, stream beds, and eroded outcrops.
Check for Alteration
The host rock immediately adjacent to a quartz vein may show signs of hydrothermal alteration (e.g., discoloration, different mineral assemblages, increased brittleness). This can be a good indicator of fluid flow.
Examine for Mineralization
Look for other minerals within the quartz vein or along its margins, such as sulfides (pyrite, chalcopyrite, galena, sphalerite), carbonates, or native metals (e.g., gold flakes), which can indicate economic potential.
Use a Hardness Test
Quartz is hard (Mohs 7). It will scratch glass and steel. This helps distinguish it from softer vein minerals like calcite.
Consider the Geological Context
Quartz veins are common in areas with a history of metamorphism, deformation, and magmatism. Consulting geological maps of an area can help identify prospective regions.
Similar Rocks
Pegmatite
Pegmatite
Also known as: Granitic Pegmatite
Aplite
Aplite
Also known as: Granitic Aplite
Chert
Chert
Also known as: Flint, Jasper
Quartzite
Quartzite
Also known as: Metaquartzite
Scientific Classification
- Mineral Class
- Silicate (Tectosilicate)
- Group
- Quartz Group
- Crystal System
- Trigonal
- Chemical Formula
- SiO2
- Composition
- Silicon dioxide (46.7% Si, 53.3% O by weight).
Explore Quartz Vein in Metamorphic Rock
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.