Chlorite-Included Quartz with Iron Staining

Mineral Aggregate/Mineral Specimen

SiO2 (Quartz) with (Mg,Fe)3(Si,Al)4O10(OH)2 (Chlorite) and Fe-oxides

Also known as: Chlorite Quartz, Iron-Stained Quartz

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Description

Quartz with Chlorite and Iron Staining is a mineral aggregate characterized by transparent to translucent quartz crystals or masses containing visible inclusions of chlorite and often exhibiting external or internal reddish-brown to yellowish-brown iron oxide staining. The chlorite typically appears as green, dark green, or black specks, flakes, or phantom growths within the quartz. The iron staining can range from superficial coatings to pervasive discoloration, often highlighting growth zones or fractures.

How to Identify

Color: Quartz matrix is typically colorless, white, or smoky. Chlorite inclusions are green, dark green, or black. Iron staining is reddish-brown, orange, or yellowish-brown.
Luster: Vitreous (glassy) for quartz; dull to pearly for chlorite inclusions; earthy to dull for iron staining.
Texture: Crystalline, often with visible quartz crystal faces. Chlorite inclusions can be flaky or fibrous. Iron staining may be powdery or a thin coating.
Crystal Form: Quartz typically forms hexagonal prisms terminated by rhombohedra. Chlorite inclusions may be disseminated flakes, radiating aggregates, or phantom layers within the quartz. Iron oxides are typically amorphous coatings or microcrystalline aggregates.
Cleavage: Quartz: None (conchoidal fracture). Chlorite: Perfect basal cleavage (one direction). Iron oxides: None.
Geological Environment: Hydrothermal veins, metamorphic rocks (e.g., greenschist facies), pegmatites, and sedimentary environments where iron-rich fluids interact with quartz-bearing rocks. Often found in areas of active faulting or alteration.

Key Facts

Hardness: Quartz: 7 on Mohs scale. Chlorite: 2-2.5. Iron oxides (e.g., goethite, hematite): 5-6.5.
Specific Gravity: Quartz: 2.65 g/cm³. Chlorite: 2.6-3.3 g/cm³. Iron oxides: 3.3-5.3 g/cm³.
Crystal System: Quartz: Trigonal. Chlorite: Monoclinic. Iron oxides: Orthorhombic (goethite), Trigonal (hematite).
Color: As described above: colorless/white/smoky quartz, green/dark green/black chlorite, reddish-brown/orange/yellowish-brown iron oxides.
Luster: Vitreous (quartz), dull to pearly (chlorite), earthy to dull (iron oxides).
Transparency: Quartz: Transparent to translucent. Chlorite: Opaque to translucent. Iron oxides: Opaque.
Fracture: Quartz: Conchoidal. Chlorite: Uneven. Iron oxides: Uneven to splintery.
Cleavage: Quartz: None. Chlorite: Perfect basal (one direction). Iron oxides: None.
Composition: Silicon dioxide (SiO2) for quartz. Hydrous magnesium iron aluminum silicate for chlorite ((Mg,Fe)3(Si,Al)4O10(OH)2). Iron oxides (e.g., FeO(OH) for goethite, Fe2O3 for hematite).

Quick Check

Color: Colorless to smoky quartz with green inclusions and reddish-brown staining.
Luster: Vitreous (quartz), dull/pearly (chlorite), earthy (iron oxides).
Streak: White (quartz), pale green (chlorite), reddish-brown to yellowish-brown (iron oxides).

Physical Characteristics

Crystal Habit: Quartz: Prismatic, massive, granular. Chlorite: Flaky, platy, massive, radiating. Iron oxides: Earthy, botryoidal, massive.
Cleavage Type: Quartz: Absent. Chlorite: Perfect in one direction {001}. Iron oxides: Absent.
Fracture Type: Quartz: Conchoidal. Chlorite: Uneven. Iron oxides: Uneven to splintery.
Tenacity: Quartz: Brittle. Chlorite: Flexible, inelastic. Iron oxides: Brittle.
Luster Type: Quartz: Vitreous. Chlorite: Dull to pearly. Iron oxides: Earthy to dull.

Formation

This material forms when quartz crystallizes or recrystallizes in the presence of chlorite and iron-bearing fluids. Chlorite inclusions typically occur during hydrothermal alteration, low-grade metamorphism, or diagenesis of mafic-rich sediments. Iron staining, primarily from goethite or hematite, results from the oxidation of iron-bearing minerals (including chlorite itself) or the precipitation of iron oxides from circulating groundwater, often as a secondary process after the initial quartz and chlorite formation.

Usage

Primarily a collector's mineral specimen. While quartz itself has numerous industrial applications (electronics, optics, abrasives), the inclusions and staining in this specific form generally preclude such uses. It is sometimes used in lapidary arts for cabochons or carvings, valued for its aesthetic appeal.

Age Distribution

Ubiquitous across geological time scales, forming in various environments from Precambrian to Cenozoic.

Where to Find

Brazil

Known for various types of included quartz, including chlorite phantoms and iron-stained varieties, particularly from Minas Gerais.

Alpine regions (e.g., Switzerland, Austria)

Classic localities for well-formed quartz crystals, often with chlorite inclusions from metamorphic environments.

United States (e.g., Arkansas, North Carolina)

Arkansas is famous for its quartz, and chlorite inclusions and iron staining are common. North Carolina also produces similar specimens from metamorphic terrains.

Madagascar

A source of various quartz types, including those with green chlorite inclusions.

Finding Tips

Look for Hydrothermal Veins

These are prime locations for quartz crystallization and the introduction of other minerals like chlorite. Look for areas with evidence of past fluid flow.

Examine Metamorphic Terrains

Low-grade metamorphic rocks, especially those derived from mafic protoliths, can host chlorite-rich quartz.

Check for Iron Staining

The reddish-brown or orange staining is a key indicator. It often occurs in weathered outcrops or near iron-rich mineral deposits.

Use a Hand Lens

Chlorite inclusions can be very fine-grained. A hand lens (10x magnification) will help distinguish the green flakes or specks within the quartz.

Distinguish from Other Green Inclusions

Be careful not to confuse chlorite with other green minerals like epidote, actinolite, or even fine-grained mica. Chlorite typically has a softer, more earthy or platy appearance compared to the often prismatic epidote or fibrous actinolite.

Similar Rocks

Epidote Quartz

SiO2 (Quartz) with Ca2(Al,Fe)3(SiO4)3(OH) (Epidote)

Also known as: Epidote-Included Quartz

Sericite Quartz

SiO2 (Quartz) with KAl2(AlSi3O10)(OH)2 (Sericite, a fine-grained muscovite)

Also known as: Sericite-Included Quartz

Actinolite Quartz

SiO2 (Quartz) with Ca2(Mg,Fe)5Si8O22(OH)2 (Actinolite)

Also known as: Actinolite-Included Quartz

Scientific Classification

Mineral Class: Quartz: Tectosilicate. Chlorite: Phyllosilicate. Iron oxides: Oxides/Hydroxides.
Group: Quartz Group, Chlorite Group, Oxide/Hydroxide Group
Crystal System: Quartz: Trigonal. Chlorite: Monoclinic. Iron oxides: Orthorhombic (Goethite), Trigonal (Hematite).
Chemical Formula: SiO2 (Quartz), (Mg,Fe)3(Si,Al)4O10(OH)2 (Chlorite, general formula), FeO(OH) (Goethite), Fe2O3 (Hematite)
Composition: Quartz is pure silicon dioxide. Chlorite is a complex hydrous magnesium iron aluminum silicate. Iron oxides are compounds of iron and oxygen, often hydrated.

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