Geological Properties of Euchlorite

 

Euchlorite is a rare, green-hued mineral belonging to the chlorite group, a family of phyllosilicate minerals known for their layered structure and mica-like texture. Although the term “euchlorite” appears in older mineralogical texts, it is now commonly classified simply as chlorite, often referring to magnesium-rich or iron-rich varieties with a distinctly rich, emerald-to-forest-green coloration.

Mineral Classification

Euchlorite is the historical or alternate name sometimes used to describe certain members of the Chlorite Group, particularly those rich in iron and magnesium. While “euchlorite” is not commonly used in modern mineral taxonomy, it aligns most closely with the species Clinochlore and sometimes Chamosite, depending on the specimen’s composition.

• Kingdom:

Mineral

• Class:

Silicates

• Subclass:

Phyllosilicates (Sheet Silicates)

• Group:

Chlorite Group

• Species Most Commonly Associated:

• • Clinochlore – Mg-rich chlorite
  • Chamosite – Fe-rich chlorite

(Euchlorite specimens tend to fall somewhere between these two endmembers.)

• Chemical Formula (Generalized Chlorite Group):

$$(Mg,Fe,Al)_6(Si,Al)_4O_{10}(OH)_8$$

(Exact chemistry varies depending on the Mg–Fe ratio and aluminum substitution.)

• Crystal System:

Monoclinic
(Some chlorite minerals may appear triclinic depending on structural distortion, but euchlorite-type specimens are typically monoclinic.)

• Crystal Habit:

Foliated masses

Micaceous sheets

Scaly aggregates

Platy or flaky growths

Fine-grained layers within metamorphic rocks

• Hardness (Mohs):

2–2.5, occasionally up to 3

• Luster:

Pearly

Vitreous

Sometimes slightly dull or earthy depending on grain size

• Streak:

Greenish-white or pale green

• Transparency:

Translucent to opaque

• Fracture & Cleavage:

Perfect basal cleavage (splits into sheets)

Fracture is uneven or micaceous

• Specific Gravity:

2.6–3.0, variable by Fe content

Group: Chlorite Group

Category: Phyllosilicate

Chemical Formula: (Varies) Commonly (Mg,Fe)_5Al(AlSi_3O_10)(OH)_8

Crystal System: Monoclinic (sometimes triclinic depending on specific variety)

Cleavage: Perfect basal cleavage

Luster: Pearly to vitreous

Transparency: Transparent to translucent

Habit: Usually found as foliated masses, flaky layers, or micaceous aggregates

Formation & Geological Environment

Euchlorite forms under low- to medium-grade metamorphic conditions, typically through the alteration of mafic minerals. It is especially common in:

 

Euchlorite/chlorite minerals form primarily through:

Low- to medium-grade metamorphism
(especially of basalt, gabbro, ultramafic rocks, shales, and pelitic rocks)

Hydrothermal alteration
(as hot fluids alter preexisting minerals, chlorite often develops as a secondary mineral)

Metasomatic processes
(chemical replacement during contact metamorphism)

Common geological settings include:

Schist and phyllite

Metamorphosed basaltic rocks

Serpentine-rich deposits

Hydrothermal alteration zones

Greenstone belts

It originates when minerals like biotite, amphibole, or pyroxene undergo chemical alteration due to heat, pressure, and interaction with hydrothermal fluids.

Color & Composition

Its iconic green color comes from variations in iron and magnesium, along with trace amounts of chromium or nickel in certain localities. The mineral’s characteristic leafy appearance and soft, earthy texture make it identifiable even in rough form.

Color Range: Light mint green to deep forest green

Streak: Pale green or white

Specific Gravity: ~2.6–3.0

Hardness: 2–2.5 on Mohs scale (very soft)

Associated Minerals

Euchlorite is a rare, green-to-dark-green mineral belonging to the chlorite group. As with most chlorite-group minerals, it commonly forms within metamorphic environments, especially those influenced by hydrothermal fluids. Because of this, Euchlorite is often found in close association with several other metamorphic and silicate minerals. These minerals develop under similar temperature–pressure conditions, making them natural companions in the geological world.

 

• Quartz

One of the most frequent minerals found near Euchlorite. Quartz forms in the same metamorphic environments and often fills fractures, veins, or pockets within chlorite-rich rocks.

• Muscovite

This shimmering mica mineral commonly occurs alongside Euchlorite in schists and altered sedimentary rocks. Both minerals are products of regional metamorphism.

• Biotite

Another mica that commonly transforms into chlorite-group minerals—including Euchlorite—during metamorphism. It often appears intermixed or adjacent to Euchlorite layers.

• Feldspar (especially Plagioclase)

Metamorphic rocks containing Euchlorite often retain remnants of feldspar, which resists alteration longer and remains as a companion mineral.

• Garnet (Almandine & Grossular)

Garnet commonly forms in the same metamorphic zones as chlorite minerals. It is frequently found embedded in schists that also contain Euchlorite.

• Epidote

A classic mineral that forms in low-to-medium-grade metamorphic rocks, epidote often grows alongside chlorite minerals due to similar formation conditions.

• Actinolite & Tremolite

These amphibole minerals frequently accompany Euchlorite in green schists and altered ultramafic environments. They share a formation environment dominated by heat, pressure, and hydrothermal activity.

• Serpentine

In ultramafic rocks, serpentine commonly appears with chlorite-group minerals. Serpentine and Euchlorite form when magnesium-rich rocks undergo hydration and metamorphism.

• Magnetite

Iron-rich metamorphic environments that host Euchlorite often also contain magnetite. It may appear as fine grains or larger crystals in the surrounding matrix.

• Talc

Present in similar low-to-medium-grade metamorphic zones, talc sometimes appears in association with Euchlorite, particularly in ultramafic terrains.

• Calcite

When hydrothermal fluids permeate metamorphic layers, calcite often forms veins alongside chlorite minerals, including Euchlorite.

These associations help crystal workers identify euchlorite in natural matrix specimens.

Locations

 

Euchlorite typically develops in metamorphic environments where heat, pressure, and chemically active fluids alter pre-existing rocks. Its presence is strongly linked with greenschist- to amphibolite-facies metamorphism, hydrothermal alteration, and low-grade metamorphosed mafic rocks.

Below are the major localities where Euchlorite (and the closely associated species in its compositional range) have been identified.

While not as widely distributed as other chlorite minerals, high-quality euchlorite deposits have been found in:

Europe

• Norway (Scandinavian Caledonides)

One of the most referenced regions for Euchlorite occurrences.
Known for chlorite-rich schists and metamorphosed volcanic sequences.

• Sweden

Found in metamorphosed greenstone belts and mica-rich schists.

• Austria

Alpine metamorphic zones contain chlorite-series minerals including euchlorite in schists and gneisses.

• Switzerland (Alps)

Common in greenschist-facies terrains.

• Italy (Alpine regions)

Forms in metamorphosed serpentinites, greenstones, and chlorite schists.

Russia

• Ural Mountains

Euchlorite appears in metamorphosed mafic and ultramafic sequences, often with amphiboles, garnet, and epidote.

North America

• Canada (British Columbia & Quebec)

Occurrences within metamorphosed volcanic belts and greenstone terrains.

• United States – Eastern Metamorphic Belts

While specific “euchlorite” labeling may vary, chlorite group minerals including euchlorite are present in:

Appalachian Mountains

New York State metamorphic belts

Vermont and New Hampshire schists

South America

• Brazil

Greenstone belts and hydrothermal alteration zones host various chlorite-series minerals including euchlorite.

 

 

Asia

• India (Himalayan Metamorphic Belt)

Widely present in greenschist, phyllite, and chlorite schists.

• Pakistan & Nepal

Common in metamorphosed ophiolite complexes and high-pressure belts.

Africa

• South Africa (Barberton Greenstone Belt)

Chlorite-rich metamorphics include members of the euchlorite series.

Geologic Environments Where Euchlorite Forms

Euchlorite is most frequently found in:

Greenschist facies metamorphic rocks

Low-grade regional metamorphism

Altered basalt, andesite, and other mafic rocks

Hydrothermally altered zones

Metamorphosed ultramafic rocks

Serpentinite-hosted environments

Its rarity in large or transparent formations makes high-grade pieces desirable among collectors and metaphysical practitioners.