Molybdenite

Molybdenite is the most important source of molybdenum, which is an important element in high-strength steels. Molybdenite was originally thought to be lead, and its name is derived from the Greek word for lead, molybdos. It was recognized as a distinct mineral by the Swedish chemist Carl Scheele in 1778. Molybdenite is soft, opaque, and bluish gray. It forms tabular hexagonal crystals, foliated masses, scales, and disseminated grains. It can also be massive or scaly. The platy, flexible, greasy-feeling hexagonal crystals of molybdenite can be confused with graphite, although molybdenite has a much higher specific gravity, a more metallic luster, and a slightly bluer tinge. Molybdenite occurs in granite, pegmatite, and hydrothermal veins at high temperature (1,065°F/575°C or above) with other minerals fluorite, ferberite, scheelite, and topaz. It is also found in porphyry ores and in contact metamorphic deposits.

Name: A word derived from the Greek molybdos, lead.

Chemistry: Nearly pure MoS2.

Polymorphism & Series: Dimorphous with jordisite; polytypes 2H1 and 3R are known.

Association: Chalcopyrite, other copper sulfides.

Molybdenite Chemical Physical and Optical Properties

Molybdenite is a naturally occurring mineral composed of molybdenum disulfide (MoS2). It is an important source of molybdenum, a transition metal with various industrial applications. Here are some of the key chemical, physical, and optical properties of molybdenite:

Chemical Properties:

1. Chemical Formula: MoS2
2. Chemical Structure: Molybdenite consists of a hexagonal lattice structure where each molybdenum atom is bonded to two sulfur atoms.

Physical Properties:

1. Color: Molybdenite is typically dark gray or metallic silver in color, but it can also appear as a bluish-gray or black.
2. Luster: It has a metallic luster, which means it reflects light like a metal.
3. Streak: The streak of molybdenite is black.
4. Hardness: Molybdenite has a hardness of approximately 1 to 1.5 on the Mohs scale. This makes it a relatively soft mineral.
5. Density: The density of molybdenite ranges from 4.7 to 5.1 grams per cubic centimeter (g/cm³).
6. Cleavage: Molybdenite exhibits perfect cleavage in one direction, which means it can be easily split into thin, flexible sheets.
7. Fracture: Its fracture is uneven or subconchoidal, meaning it breaks with irregular, non-smooth surfaces.
8. Crystal System: Molybdenite crystallizes in the hexagonal crystal system.

Optical Properties:

1. Transparency: Molybdenite is typically opaque, meaning it does not allow light to pass through it.
2. Refractive Index: The refractive index of molybdenite is generally not applicable because it is opaque.
3. Birefringence: Molybdenite is non-birefringent, meaning it does not exhibit double refraction.
4. Pleochroism: It may exhibit weak pleochroism, where it appears slightly different in color or intensity when viewed from different angles, but this effect is usually minimal.

Molybdenite is often associated with other minerals in ore deposits and is an important source of molybdenum, which is used in the production of steel, alloys, and various industrial applications. Its unique physical properties, such as its cleavage and lubricity, also make it useful in certain specialized applications, including as a dry lubricant in high-temperature environments.

Molybdenite Occurrence and Formation

Molybdenite, a mineral composed of molybdenum disulfide (MoS2), occurs naturally in various geological settings. Its formation is closely linked to the geological processes and conditions under which it crystallizes. Here’s a brief overview of the occurrence and formation of molybdenite:

1. Geologic Occurrence:

• Molybdenite is commonly found in association with other ore minerals in hydrothermal vein deposits, which are fractures or veins in rocks filled with mineral-rich fluids. These deposits often occur in igneous and metamorphic rocks.
• Molybdenite can also be found in sedimentary rocks, but these occurrences are less common and often result from the re-deposition of molybdenite-bearing material transported by water.
• It is frequently associated with minerals such as quartz, fluorite, pyrite, and tungsten minerals.

2. Formation Process:

• Molybdenite forms primarily through hydrothermal processes, which involve the circulation of hot, mineral-rich fluids through cracks and fissures in the Earth’s crust. These fluids are typically associated with igneous intrusions and volcanic activity.
• The formation of molybdenite typically occurs under high-temperature and high-pressure conditions.
• The key steps in the formation of molybdenite are as follows: a. Molybdenum and sulfur are sourced from the surrounding rocks or magma. b. These elements combine to form molybdenite crystals as the hydrothermal fluids cool and react with the host rocks. c. Molybdenite crystallizes in a hexagonal lattice structure, where each molybdenum atom is bonded to two sulfur atoms. d. The mineral may form well-defined crystals or occur as disseminated flakes within the host rock.

3. Geological Environments:

• Molybdenite is commonly associated with granitic intrusions, which can be sources of molybdenum and sulfur. These intrusions are often found in mountain-building regions and plate tectonic boundaries.
• It can also occur in skarn deposits, which are formed at the contact between carbonate rocks and intrusive igneous rocks.
• Porphyry copper deposits frequently contain molybdenite as a byproduct mineral, as molybdenum often accompanies copper in these deposits.

The economic significance of molybdenite is largely due to its occurrence in these hydrothermal ore deposits, where it can be extracted and processed to obtain molybdenum. Molybdenum has numerous industrial applications, including in the production of steel and alloys, as a catalyst in chemical processes, and as an essential trace element in plant and animal nutrition. Understanding the geological processes that lead to molybdenite formation is crucial for locating and exploiting economically viable deposits.

Molybdenite Application and Uses Areas

Molybdenite, primarily composed of molybdenum disulfide (MoS2), is a valuable mineral with a wide range of applications in various industries. Molybdenum, the key element in molybdenite, exhibits unique properties that make it essential in several important applications and use areas:

1. Alloy Production:

• Molybdenum is used to produce various high-strength alloys. When added to steel and other metals, it enhances their mechanical properties, such as strength, hardness, and resistance to corrosion and high temperatures.
• Common alloys include molybdenum steel (high-speed steel), which is used for cutting tools and in the automotive and aerospace industries.

2. Stainless Steel Production:

• Molybdenum is a crucial alloying element in the production of stainless steel. It improves the corrosion resistance of stainless steel, especially in aggressive environments, such as those containing acids or chlorides.
• Stainless steel is widely used in the construction, food processing, chemical, and aerospace industries.

3. Electronics and Electrical Applications:

• Molybdenum and molybdenum disilicide (MoSi2) are used in the production of heating elements, filaments, and electrical contacts due to their high melting points and electrical conductivity.
• Molybdenum is also used as a back contact material in thin-film solar cells.

4. Lubricants:

• Molybdenum disulfide has exceptional lubricating properties, even at high temperatures and under extreme pressure. It is used as a solid lubricant in various applications, including automotive and industrial equipment.

5. Catalysts:

• Molybdenum compounds, such as molybdenum trioxide (MoO3), are used as catalysts in chemical reactions, such as the refining of petroleum and the production of chemicals and polymers.

6. Aerospace and Defense:

• Molybdenum is used in aerospace applications due to its high-temperature resistance and strength. It is used in aircraft components, rocket engines, and missile systems.

7. Energy Industry:

• Molybdenum is used in the production of equipment for the energy sector, including components in nuclear power plants and oil refineries.

8. Glass and Ceramics:

• Molybdenum is used as electrodes in the production of specialized glass and ceramics, such as glass-to-metal seals and insulating ceramics.

9. Metallurgy:

• Molybdenum is used as a refractory material in metallurgical applications, such as the production of iron and non-ferrous metals. It can withstand high temperatures and harsh conditions.

10. Environmental Applications: – Molybdenum is used in catalytic converters to reduce emissions from automobiles, helping to reduce air pollution.

Molybdenum’s versatility and unique properties make it a critical element in several industries, and its applications continue to expand as technology advances. Its ability to enhance the performance of materials in high-stress, high-temperature, and corrosive environments ensures its continued importance in various sectors.

Distribution

Of widespread occurrence; the most abundant molybdenum mineral.

• Fine crystals occur, in the USA, at the Crown Point mine, Lake Chelan, Chelan Co., Washington; and at the Frankford quarry, Philadelphia, Pennsylvania.
• In Canada, in the Temiskaming district, and in Aldfield Township, Quebec.
• In Norway, from Raade, near Moss, and at Vennesla, near Arendal.
• In Russia, in the Adun-Chilon Mountains, south of Nerchinsk, Transbaikal; at Miass, Ilmen Mountains, Southern Ural Mountains; and in the Slundyanogorsk deposit, Central Ural Mountains.
• In Germany, at Altenberg, Saxony.
• In Morocco, at Azegour, 80 km southwest of Marrakesh.
• From Kingsgate and Deepwater, New South Wales, Australia.
• At the Hirase mine, Gifu Prefecture, Japan.
• In the Wolak mine, Danyang, Chungchong Province, South Korea.
• The 3R polytype occurs in the Con mine, Yellowknife, Yukon Territory; and at Mont Saint-Hilaire, Quebec, Canada.
• From the Yamate mine, Okayama Prefecture, Japan.

References

• Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
• Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
• Mindat.org. (2019). Molybdenite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].