Basalt with Quartz Veins

Igneous (extrusive) with hydrothermal alteration

Basalt (mafic volcanic rock) with Quartz (SiO2) veins

Also known as: Quartz-veined Basalt

Got a photo? Identify rocks instantly with the Rockby app

Description

Basalt with quartz veins is a composite geological material consisting of a dark, fine-grained mafic igneous rock (basalt) cut by lighter-colored, typically white to translucent, crystalline veins of quartz. The basalt matrix is usually black, dark gray, or greenish-black, and can be aphanitic (fine-grained) or porphyritic (containing larger crystals within a fine-grained matrix). The quartz veins vary in thickness from hairline fractures to several centimeters wide, and the quartz crystals within them can be massive, granular, or well-formed euhedral crystals, sometimes exhibiting drusy textures.

How to Identify

Color: Basalt matrix is typically dark gray to black; quartz veins are usually white, clear, or milky, sometimes stained by iron oxides (red/brown).
Luster: Basalt matrix is dull to sub-vitreous; quartz veins are vitreous (glassy).
Texture: Basalt is fine-grained (aphanitic) or porphyritic; quartz veins are crystalline, ranging from massive to granular to well-formed crystals.
Crystal Form: Basalt minerals are typically microscopic; quartz in veins can be anhedral (massive) to euhedral (well-formed hexagonal prisms with pyramidal terminations).
Cleavage: Basalt minerals (pyroxene, plagioclase) have cleavage, but it's rarely visible in hand specimen due to fine grain size. Quartz has no cleavage, exhibiting conchoidal fracture.
Geological Environment: Volcanic terrains, rift zones, oceanic crust, large igneous provinces, often in areas that have experienced post-emplacement hydrothermal activity or tectonic fracturing.

Key Facts

Hardness: Basalt (variable, typically 5-6 on Mohs scale for constituent minerals); Quartz (7 on Mohs scale)
Specific Gravity: Basalt (2.8-3.0 g/cm³); Quartz (2.65 g/cm³)
Crystal System: Basalt (polycrystalline, constituent minerals are monoclinic, triclinic, or orthorhombic); Quartz (Trigonal)
Color: Basalt (dark gray, black, greenish-black); Quartz (colorless, white, milky, sometimes tinted by impurities)
Luster: Basalt (dull, earthy, sub-vitreous); Quartz (vitreous)
Transparency: Basalt (opaque); Quartz (transparent to translucent)
Fracture: Basalt (uneven, hackly); Quartz (conchoidal)
Cleavage: Basalt (poor to absent in hand specimen); Quartz (none)
Composition: Basalt (primarily plagioclase feldspar, pyroxene, olivine, magnetite); Quartz (SiO2)

Quick Check

Color: Dark (basalt) with white/clear (quartz) veins
Luster: Dull to sub-vitreous (basalt) and vitreous (quartz)
Streak: White (quartz) on a streak plate; basalt typically has no streak or a very faint grayish streak.

Physical Characteristics

Crystal Habit: Basalt (aphanitic to porphyritic, massive); Quartz (massive, granular, prismatic crystals in veins)
Cleavage Type: Basalt (not typically observed in hand specimen); Quartz (none)
Fracture Type: Basalt (uneven, hackly); Quartz (conchoidal)
Tenacity: Basalt (brittle); Quartz (brittle)
Luster Type: Basalt (dull, earthy, sub-vitreous); Quartz (vitreous)

Formation

Basalt forms from the rapid cooling of mafic lava at or near the Earth's surface. Quartz veins form later, typically through hydrothermal processes where hot, silica-rich fluids circulate through fractures and fissures within the pre-existing basalt. As these fluids cool or undergo pressure changes, dissolved silica precipitates as quartz.

Usage

While basalt itself is widely used in construction (aggregate, road base, building stone), and quartz has numerous industrial applications (electronics, optics, abrasives), basalt with quartz veins is generally not sought for specific industrial uses due to its heterogeneous nature. It can be collected as a geological specimen, showcasing secondary mineralization.

Age Distribution

Basalt is common throughout Earth's history, from the Precambrian to the present. Quartz veins can form at various times after the basalt's initial emplacement, often associated with later tectonic or hydrothermal events.

Where to Find

Mid-Ocean Ridges and Oceanic Islands

Basalt is the primary rock of the oceanic crust. Hydrothermal vents and associated fracturing can lead to quartz vein formation.

Continental Flood Basalt Provinces

Regions like the Deccan Traps (India), Columbia River Basalt Group (USA), and Siberian Traps (Russia) where massive basalt flows occurred, often with subsequent fracturing and hydrothermal alteration.

Volcanic Arcs and Subduction Zones

Areas with active or ancient volcanism where basaltic lavas are common, and tectonic stresses create fractures for fluid circulation.

Rift Valleys

Regions where continental crust is pulling apart, leading to basaltic volcanism and subsequent fracturing.

Finding Tips

Look for Fractures

Quartz veins are secondary features that fill fractures. Examine basalt outcrops for linear or irregular cracks filled with lighter-colored material.

Check for Hydrothermal Alteration

Areas with quartz veins often show other signs of hydrothermal alteration in the surrounding basalt, such as discoloration, presence of secondary minerals (e.g., chlorite, epidote), or vugs.

Examine Road Cuts and Quarries

These exposures often provide fresh surfaces where veins are more easily visible than on weathered surfaces.

Use a Hand Lens

A hand lens (10x magnification) can help distinguish the fine-grained basalt matrix from the crystalline quartz within the veins.

Similar Rocks

Andesite with Quartz Veins

Andesite (intermediate volcanic rock) with Quartz (SiO2) veins

Also known as: Quartz-veined Andesite

Diorite with Quartz Veins

Diorite (intermediate intrusive rock) with Quartz (SiO2) veins

Also known as: Quartz-veined Diorite

Gabbro with Quartz Veins

Gabbro (mafic intrusive rock) with Quartz (SiO2) veins

Also known as: Quartz-veined Gabbro

Scientific Classification

Mineral Class: Basalt (Igneous Rock); Quartz (Silicate Mineral)
Group: Basalt (Volcanic Rock); Quartz (Tectosilicate)
Crystal System: Basalt (Polycrystalline); Quartz (Trigonal)
Chemical Formula: Basalt (complex silicate mixture); Quartz (SiO2)
Composition: Basalt (mafic, rich in Fe, Mg, Ca, Al, Si); Quartz (Silicon Dioxide)

Explore Basalt with Quartz Veins

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