Chlorite is a mineral and chemical compound with several different meanings and applications in various fields, including geology, chemistry, and industrial processes. This introduction will provide an overview of chlorite from both geological and chemical perspectives.

1. Geological Perspective: Chlorite as a mineral is part of the phyllosilicate group, which includes minerals with a layered structure. It is characterized by its greenish color, foliated appearance, and relatively low hardness. Chlorite minerals are commonly found in metamorphic rocks, where they form as a result of the alteration of other minerals, such as biotite, amphibole, and pyroxene, under conditions of low to moderate temperature and pressure.

Key characteristics of chlorite minerals include their platy or micaceous texture and a tendency to occur in thin, flexible flakes. They are often associated with rocks like schist, slate, and phyllite. Chlorite minerals can vary in composition, but they typically contain silicon, aluminum, oxygen, hydrogen, and various metallic elements like iron and magnesium.

2. Chemical Perspective: From a chemical standpoint, chlorite can also refer to a specific chemical compound known as chlorite ion (ClO2-), which is a polyatomic anion. Chlorite ions are made up of one chlorine atom (Cl) bonded to two oxygen atoms (O) and one additional electron, giving them a negative charge. Chlorite ions are the building blocks of various chlorite salts and compounds.

One notable chlorite compound is sodium chlorite (NaClO2), which is used in various industrial processes, including water treatment and as a precursor in the production of chlorine dioxide (ClO2). Chlorine dioxide is a powerful disinfectant and bleaching agent, and it has applications in the paper and pulp industry, as well as in the treatment of drinking water and wastewater.

In summary, chlorite can refer to both a group of greenish minerals found in metamorphic rocks and a chemical compound involving chlorite ions. Its geological presence is significant in understanding rock formations and metamorphism, while its chemical properties have practical applications in various industries.

Name: Chlorite is derived from a Greek word meaning green, in allusion to the common color of the mineral.

Diagnostic Features: Characterized by its green color, micaceous habit and cleavage, and by the fact that the folia are not elastic.

Chlorite Occurrence and Formation

Chlorite formation and occurrence are closely tied to geological processes, and understanding how chlorite is formed and where it is found can provide valuable insights into the Earth’s history and the characteristics of specific rock formations. Here’s an overview of chlorite formation and its occurrence:

Formation of Chlorite: Chlorite minerals typically form through a process called metamorphism, which involves the alteration of pre-existing rocks under specific temperature and pressure conditions. The formation of chlorite is associated with low to moderate metamorphic conditions, often occurring in the greenschist facies of metamorphism. Here’s how chlorite is formed:

  1. Parent Minerals: Chlorite minerals commonly originate from the alteration of other minerals, such as biotite (a mica mineral), amphibole, or pyroxene. These parent minerals contain elements like iron, magnesium, silicon, and aluminum.
  2. Metamorphic Conditions: Chlorite formation usually takes place at temperatures between 200°C and 400°C and at relatively low to moderate pressures. These conditions are commonly found in regions undergoing regional metamorphism, where tectonic forces cause rocks to be subjected to heat and pressure.
  3. Hydrothermal Activity: Chlorite can also form as a result of hydrothermal activity, where hot fluids percolate through rocks, altering their mineral composition. This process can occur in a variety of geological settings, including near hydrothermal vents on the ocean floor and in mineral veins.

Occurrence of Chlorite: Chlorite minerals are commonly found in various geological settings and rock types. Here are some of the common occurrences:

  1. Metamorphic Rocks: Chlorite is often associated with metamorphic rocks, especially those formed under greenschist facies conditions. These rocks include chlorite schist, chlorite slate, and phyllite. Chlorite’s greenish color can give these rocks their distinctive appearance.
  2. Hydrothermal Deposits: In hydrothermal systems, chlorite can be present in the alteration zones surrounding ore deposits. It may be associated with minerals like quartz, sulfides, and carbonate minerals.
  3. Sedimentary Rocks: While less common, chlorite can also be found in some sedimentary rocks, such as shale and mudstone. In these cases, it may have formed during diagenesis, which is the chemical and physical alteration of sediments into sedimentary rocks.
  4. Soil and Weathering Products: Weathering of rocks containing chlorite can release chlorite minerals into the soil, where they contribute to the mineral composition of the Earth’s crust.
  5. Geothermal Springs: In geothermal environments, chlorite can be found in the precipitates that form around hot springs and geysers.

Overall, chlorite is a mineral that occurs in a wide range of geological settings, with its formation primarily tied to metamorphic processes and hydrothermal activity. Its presence in rocks provides important clues about the history and conditions under which those rocks formed, making it a valuable mineral for geologists and researchers studying Earth’s history and processes.

Types of Chlorite

Chlorite is a mineral group with several different species and varieties, each with its own unique characteristics. Here are some of the common types of chlorite, their varieties, and notable localities where they are found:

Clinochlore with Calcite

1. Clinochlore: Clinochlore is one of the most well-known chlorite minerals and is often used as a generic term for chlorite in its mineralogical sense. It has a monoclinic crystal structure and is typically green to blackish-green in color. Varieties of clinochlore include:

  • Cookeite: A variety of clinochlore that occurs as fine, scaly aggregates. It is commonly found in clay-rich environments.
  • Kämmererite: A chromium-rich variety of clinochlore that exhibits a striking violet-red to pink color. It is a rare variety often found in metamorphic rocks.

Notable Localities: Clinochlore can be found in various metamorphic rocks worldwide. Specific localities include Switzerland, Italy, the United States (especially in New Jersey and Pennsylvania), and Norway.


2. Chamosite: Chamosite is another chlorite variety that has a monoclinic crystal structure. It is typically green to dark green in color and often occurs as fine-grained aggregates.

Notable Localities: Chamosite is found in various metamorphic and sedimentary rocks. It is known from localities in France, Germany, the United Kingdom, and the United States.

3. Orthochamosite: Orthochamosite is a rare orthorhombic variety of chlorite. It is typically dark green to blackish-green and can be found in metamorphic rocks.

Notable Localities: Orthochamosite has been reported from localities in Austria, Switzerland, and the United States.

4. Pennine: Pennine is a chlorite variety that is often associated with Alpine-type fissures and hydrothermal veins. It is known for its striking green color.

Notable Localities: Pennine chlorite is found in the Swiss and Italian Alps, as well as in the Pennines of England, from which it derives its name.

5. Thuringite: Thuringite is a chlorite variety that contains significant amounts of manganese. It is typically dark green to blackish-green and is commonly found in manganese deposits.

Notable Localities: Thuringite is known from Thuringia, Germany, and other manganese ore deposits around the world.

6. Ripidolite: Ripidolite is a variety of chlorite that is often associated with talc deposits. It is typically light green to grayish-green and is known for its soft, platy texture.

Notable Localities: Ripidolite can be found in talc deposits in countries such as Italy, the United States (Vermont), and Canada.

7. Kammererite: As mentioned earlier, kammererite is a variety of clinochlore that is notable for its violet-red to pink color. It is often found in association with chromite deposits.

Notable Localities: Kammererite is known from localities in Turkey, Russia, and South Africa.

These varieties of chlorite are found in a range of geological settings, including metamorphic rocks, hydrothermal veins, and ore deposits. Their unique properties and colors make them of interest to mineral collectors and researchers studying the Earth’s crust and geological history.

chlorite under the microscope

Physical, Chemical and Optical Properties

Chlorite is a group of phyllosilicate minerals with varying physical, chemical, and optical properties, depending on the specific species and composition within the group. Here are some general characteristics and properties associated with chlorite:

Physical Properties:

  1. Color: Chlorite minerals can exhibit a range of colors, but they are most commonly green, varying from pale green to dark green. The green color is due to the presence of iron and other elements within the crystal structure.
  2. Luster: Chlorite minerals typically have a pearly or vitreous (glassy) luster when viewed in thin flakes.
  3. Streak: The streak of chlorite minerals is usually white to pale green.
  4. Transparency: Chlorite minerals are often translucent to nearly opaque. Their thin flakes can be somewhat transparent when backlit.
  5. Crystal Habit: Chlorite minerals have a platy or foliated crystal habit, forming thin, flexible flakes or sheets. They can also occur as fine-grained aggregates.
  6. Cleavage: Chlorite minerals exhibit one perfect cleavage plane parallel to the basal plane of their crystal structure. This cleavage produces thin, flat flakes.
  7. Hardness: The hardness of chlorite minerals on the Mohs scale typically ranges from 2 to 2.5, making them relatively soft.
  8. Specific Gravity: The specific gravity of chlorite minerals varies depending on their composition, but it generally falls in the range of 2.6 to 3.3.

Chemical Properties:

  1. Chemical Composition: Chlorite minerals are complex silicate minerals that contain silicon (Si), oxygen (O), aluminum (Al), iron (Fe), magnesium (Mg), and hydrogen (H). The exact chemical composition can vary between different chlorite species and varieties.
  2. Formula: The general formula for chlorite is (Mg,Fe)3(Si,Al)4O10(OH)2(O,OH)2·(Mg,Fe)3(OH)6.
  3. Stability: Chlorite is stable under low to moderate temperature and pressure conditions, making it a common alteration mineral in metamorphic rocks.

Optical Properties:

  1. Refractive Index: Chlorite minerals have a refractive index that falls in the range of 1.56 to 1.64, depending on the specific composition and variety.
  2. Birefringence: Chlorite minerals typically exhibit low birefringence, which means that they do not produce significant interference colors when viewed under a polarizing microscope.
  3. Pleochroism: Some chlorite varieties may show weak pleochroism, meaning they can exhibit subtle color variations when viewed from different angles.
  4. Transparency: Chlorite minerals are usually translucent to nearly opaque, with thin flakes being more transparent than thicker sections.

In summary, chlorite is a group of phyllosilicate minerals with a distinct green color, platy or foliated crystal habit, and relatively low hardness. Their chemical composition can vary, but they typically contain elements such as silicon, aluminum, iron, magnesium, and hydrogen. Chlorite minerals have specific optical properties, including refractive indices, birefringence, and pleochroism, that can vary depending on their specific species and composition. These properties make chlorite minerals important in both geological and mineralogical studies.

Uses and Application of Chlorite

Chlorite, both in its mineral form and as a chemical compound, has several uses and applications across various industries and scientific fields. Here are some of the key uses and applications of chlorite:

1. Industrial Water Treatment:

  • Chlorite compounds, particularly sodium chlorite (NaClO2), are used in industrial water treatment processes. When activated with an acid, sodium chlorite generates chlorine dioxide (ClO2), a powerful disinfectant and oxidizing agent. Chlorine dioxide is effective in treating water for bacteria, viruses, and other microorganisms. It is also used to control taste and odor issues in drinking water.

2. Pulp and Paper Industry:

  • Chlorine dioxide (ClO2), produced from sodium chlorite, is a crucial bleaching agent used in the pulp and paper industry. It helps whiten and brighten paper products while minimizing the environmental impact compared to traditional chlorine-based bleaching processes.

3. Oil and Gas Industry:

  • Chlorite-based solutions are used in the oil and gas industry for drilling mud applications. These solutions can help control the viscosity and stabilize the drilling mud during drilling operations.

4. Disinfection and Sanitization:

  • Chlorine dioxide (ClO2), derived from chlorite compounds, is employed for disinfection and sanitization purposes in various settings, including hospitals, food processing facilities, and municipal water treatment plants.

5. Food Industry:

  • Chlorine dioxide is approved for use as a food disinfectant and preservative by regulatory agencies in some countries. It can be used to sanitize food contact surfaces, equipment, and to treat food products directly.

6. Remediation of Mold and Mildew:

  • Chlorine dioxide can be used to remediate mold and mildew problems in buildings. It is effective in killing mold spores and preventing their regrowth.

7. Agricultural Applications:

  • Chlorine dioxide can be used in agriculture to disinfect irrigation water, sanitize equipment, and control bacterial and fungal diseases in crops.

8. Biomedical Research:

  • Chlorite compounds are sometimes used in laboratory research, particularly in studies involving oxidative stress and cellular responses to oxidative damage.

9. Geological Studies:

  • Chlorite minerals are valuable to geologists and mineralogists for understanding the metamorphic history of rocks and studying geological processes. They can provide insights into temperature and pressure conditions during rock formation.

10. Art and Gemology:

  • Chlorite-included quartz crystals are prized by mineral collectors and are used in jewelry making. These quartz crystals, known as “chlorite phantom quartz” or “chlorite inclusions,” have intriguing green chlorite inclusions that add beauty and value to the gemstone.

It’s important to note that the use of chlorite compounds should be handled with care, as they can be hazardous in concentrated forms. Safety protocols and regulations should be followed when using chlorite-based chemicals, particularly in industrial and water treatment applications. Additionally, regulations regarding the use of chlorine dioxide in food processing and water treatment can vary by region and should be adhered to accordingly.

Notable Deposits and Locations

Chlorite minerals and chlorite deposits can be found in various geological settings around the world. These deposits are associated with specific rock types and geological processes. Here are some notable deposits and locations where chlorite minerals can be found:

  1. Swiss Alps (Switzerland): The Swiss Alps are known for their rich chlorite deposits, particularly in regions like the Engadin Window. Chlorite minerals, including clinochlore and pennine, can be found in metamorphic rocks within these mountainous areas.
  2. Italian Alps (Italy): Similar to the Swiss Alps, the Italian Alps also host chlorite-rich metamorphic rocks. The Val Malenco region in northern Italy is known for its chlorite schists and other chlorite-bearing rocks.
  3. Austrian Alps (Austria): Chlorite minerals, including clinochlore and orthochamosite, are found in various metamorphic rocks in the Austrian Alps, especially in regions like Tyrol.
  4. New Jersey (USA): New Jersey is renowned for its extensive chlorite deposits, particularly in the Highlands region. The state’s geology features numerous chlorite-rich schist and slate formations.
  5. Pennsylvania (USA): Pennsylvania is another state in the United States known for its chlorite-rich metamorphic rocks. Chlorite minerals can be found in various regions, including the Reading Prong and the Appalachian Mountains.
  6. Scotland (United Kingdom): The Scottish Highlands contain chlorite schist and phyllite formations, where chlorite minerals are commonly associated with metamorphic rocks.
  7. Norway: Norway is home to chlorite deposits found in metamorphic rocks within the Scandinavian mountain ranges, including the Caledonides.
  8. Grenville Province (Canada): The Grenville Province in eastern Canada contains chlorite-rich metamorphic rocks, particularly in regions like the Adirondack Mountains of New York and the Grenville Front in Quebec.
  9. Oman: In Oman, chlorite minerals can be found in ophiolitic rocks, which are part of the Oman Ophiolite Complex. These rocks have been uplifted and exposed due to tectonic processes.
  10. South Africa: South Africa hosts chlorite deposits associated with various geological formations, including metamorphic rocks and hydrothermal veins. Notable localities include the Barberton Greenstone Belt.
  11. Brazil: Chlorite minerals can be found in several Brazilian states, often associated with metamorphic rocks. Regions like Minas Gerais are known for their chlorite-bearing geological formations.
  12. Antarctica: Chlorite minerals have been discovered in Antarctic rocks, particularly in the mountain ranges of the continent. These rocks provide insights into Antarctica’s geological history.

These locations represent just a portion of the global distribution of chlorite deposits. Chlorite minerals are widespread and can be found in a variety of geological environments, including metamorphic rocks, hydrothermal deposits, and ophiolitic complexes. They are valuable to geologists and mineral enthusiasts for understanding Earth’s geological history and processes.