Quartz with Pyrite

Mineral Association

SiO2 (Quartz) with FeS2 (Pyrite)

Also known as: Pyritic Quartz, Auriferous Quartz (if gold is present)

Got a photo? Identify rocks instantly with the Rockby app

Description

Quartz with pyrite refers to an association where crystals or masses of pyrite (iron disulfide) are found within or intimately associated with quartz (silicon dioxide). This combination is very common in many geological settings, particularly in hydrothermal vein systems. The pyrite typically appears as metallic, brassy-yellow crystals, often cubic, pyritohedral, or octahedral, embedded within or coating translucent to opaque quartz. The quartz can range from massive to well-crystallized, and its color can vary from clear to milky white, gray, or even amethystine, depending on impurities and formation conditions.

How to Identify

Color: Quartz: Colorless, white, gray, purple (amethyst), yellow (citrine), pink (rose quartz), brown (smoky quartz). Pyrite: Pale brass-yellow, metallic.
Luster: Quartz: Vitreous (glassy). Pyrite: Metallic.
Texture: Can range from massive intergrowths to well-formed quartz crystals hosting distinct pyrite crystals. Quartz can be granular, crystalline, or cryptocrystalline. Pyrite crystals are typically euhedral to subhedral.
Crystal Form: Quartz: Hexagonal prisms terminated by rhombohedra. Pyrite: Cubes, pyritohedra, octahedra, often striated.
Cleavage: Quartz: None (conchoidal fracture). Pyrite: Indistinct on {001}.
Geological Environment: Hydrothermal veins, porphyry deposits, volcanogenic massive sulfide (VMS) deposits, sedimentary rocks (as concretions or disseminations).

Key Facts

Hardness: Quartz: 7 on Mohs scale; Pyrite: 6-6.5 on Mohs scale.
Specific Gravity: Quartz: 2.65 g/cm³; Pyrite: 4.95-5.10 g/cm³.
Crystal System: Quartz: Trigonal; Pyrite: Isometric.
Color: Quartz: Colorless, white, gray, purple, yellow, pink, brown; Pyrite: Pale brass-yellow.
Luster: Quartz: Vitreous; Pyrite: Metallic.
Transparency: Quartz: Transparent to opaque; Pyrite: Opaque.
Fracture: Quartz: Conchoidal; Pyrite: Uneven to conchoidal.
Cleavage: Quartz: None; Pyrite: Indistinct on {001}.
Composition: Quartz: Silicon dioxide (SiO2); Pyrite: Iron disulfide (FeS2).

Quick Check

Color: Quartz: Variable (clear, white, gray, etc.); Pyrite: Brassy yellow.
Luster: Quartz: Vitreous; Pyrite: Metallic.
Streak: Quartz: White; Pyrite: Greenish-black to brownish-black.

Physical Characteristics

Crystal Habit: Quartz: Prismatic, massive, granular, cryptocrystalline; Pyrite: Cubic, pyritohedral, octahedral, massive, granular, radiating.
Cleavage Type: Quartz: Absent; Pyrite: Indistinct.
Fracture Type: Quartz: Conchoidal; Pyrite: Uneven to conchoidal.
Tenacity: Quartz: Brittle; Pyrite: Brittle.
Luster Type: Quartz: Vitreous; Pyrite: Metallic.

Formation

Quartz with pyrite typically forms in hydrothermal environments, where hot, mineral-rich fluids circulate through fractures and pores in rocks. Pyrite often precipitates alongside quartz due to changes in temperature, pressure, and fluid chemistry (e.g., pH, redox potential). It is common in mesothermal and epithermal vein deposits, porphyry copper deposits, and volcanogenic massive sulfide (VMS) deposits. Pyrite can also form in sedimentary environments under anoxic conditions.

Usage

While quartz itself has numerous industrial uses (e.g., electronics, glass, abrasives), and pyrite is a minor source of sulfur and historically used for sulfuric acid production, the primary significance of quartz with pyrite is as an indicator mineral for various ore deposits, particularly those containing gold (auriferous quartz veins). It is also highly valued by mineral collectors for its aesthetic appeal.

Age Distribution

Found in geological formations ranging from Precambrian to Cenozoic, depending on the specific ore-forming event.

Where to Find

Worldwide in hydrothermal vein systems

Common in gold, silver, copper, and lead-zinc deposits globally. Notable occurrences include the Mother Lode in California (USA), various deposits in Peru, Mexico, Australia, and Canada.

Porphyry Copper Deposits

Large, low-grade copper deposits often associated with intrusive igneous rocks, where pyrite is a common accessory mineral within quartz veins and disseminations (e.g., Chuquicamata, Chile; Bingham Canyon, USA).

Volcanogenic Massive Sulfide (VMS) Deposits

Formed on or below the seafloor in volcanic settings, these deposits often contain significant pyrite and quartz (e.g., Kidd Creek, Canada; Kuroko deposits, Japan).

Sedimentary Rocks

Pyrite can form diagenetically in shales, coals, and other organic-rich sediments, sometimes associated with authigenic quartz or as concretions. However, this association is typically less prominent than in hydrothermal settings.

Finding Tips

Look for Veins

Quartz with pyrite is most commonly found in quartz veins cutting through host rocks, especially in areas known for metallic mineral deposits.

Identify Alteration Zones

Hydrothermal alteration (e.g., sericitization, silicification, pyritization) often accompanies the formation of quartz-pyrite assemblages. Look for discolored or altered host rocks.

Check Mine Dumps and Prospect Pits

Historical mining areas are excellent places to find specimens, as miners often discarded material not rich enough in the primary ore metal.

Use a Hand Lens

A hand lens (10x magnification) is invaluable for identifying small pyrite crystals embedded within quartz and observing their characteristic metallic luster and crystal forms.

Similar Rocks

Quartz with Chalcopyrite

SiO2 (Quartz) with CuFeS2 (Chalcopyrite)

Also known as: Chalcopyritic Quartz

Quartz with Arsenopyrite

SiO2 (Quartz) with FeAsS (Arsenopyrite)

Also known as: Arsenopyritic Quartz

Quartz with Marcasite

SiO2 (Quartz) with FeS2 (Marcasite)

Also known as: Marcasitic Quartz

Scientific Classification

Mineral Class: Quartz: Tectosilicate; Pyrite: Sulfide.
Group: Quartz: Quartz Group; Pyrite: Pyrite Group.
Crystal System: Quartz: Trigonal; Pyrite: Isometric.
Chemical Formula: SiO2 (Quartz) and FeS2 (Pyrite)
Composition: Quartz: Silicon (46.7%) and Oxygen (53.3%); Pyrite: Iron (46.55%) and Sulfur (53.45%).

Explore Quartz with Pyrite

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