Iron Minerals

(1). Magnetite: Fe3O4

Magnetite; an important iron mineral

Physical properties of Magnetite:

  • Crystal System: cubic
  • Cleavage: Absent
  • Hardness: 6 in Moh’s scale
  • Sp.Gr: 5.18
  • Lustre: metallic to dull
  • Colour: Iron Black
  • Special Character: Strongly magnetic. A natural magnet is called ”Iodestone”.
  • Habit: Octahedral crystals, massive or granular.

Occurrence of Magnetite:

Magnetite is a high-temperature mineral, which occurs as an accessory mineral found in igneous rocks, contact and regionally metamorphosed rocks, and high-temperature sulfide veins.

Uses of Magnetite:

  • Magnetite is an important ore of iron, thus used to extract iron.
  • Magnetite is used to make magnets, which are used in electric motors, dynamos, loudspeakers, microphones, magnetic compass, doorbells, and refrigerators.
  • Ceramic magnets are used in computers.
  • Magnets are used in toys to give a magic effect.
  • Magnetite is used in the foundry as a sand additive to prevent surface defects of the casted metal.
  • Magnetite is also used as heat storage.

(2). Hematite: Fe3O4

Physical properties of Hematite:

  • Crystal System: trigonal
  • Cleavage: Absent
  • Hardness: 5-6 in Moh’s scale
  • Sp.Gr: 5.26
  • Lustre: metallic to dull
  • Colour: Redish brown to black
  • Streak: Dark Red
  • Special Character: A magnetic material.
  • Habit: Thin tabular, usually massive. It may also be micaceous and foliated.
  • Varieties:
    • Red Earthy variety is called ”Red Ocher”.
    • Platy and metallic variety is known as ”specularite”.

Occurrence of Hematite:

The hematite is found in the thick beds of sedimentary origins. It is also found in metamorphosed sediments and contact metamorphic deposits.

Uses of Hematite:

  • Red ocher is a type of hematite, which is used as a pigment.
  • Hematite is a good source of iron.
  • Hematite also has magnetic effects, which can be used in place of magnetite.
  • Hematite is also used as a gem material.
  • Hematite is also used for metaphysical purposes. It can be used as a healing stone. It is said that keeping hematite will resist many health issues.

(3). Goethite: Fe3O4 OH

Physical properties of Goethite:

  • Crystal System: orthorhombic
  • Cleavage: perfect
  • Hardness: 5- 5.5 in Moh’s scale
  • Sp.Gr: 3.3 – 4.3
  • Lustre: Adamentine to dull. Silky in fibrous varieties.
  • Colour: Goethite is found in dark-brown colour to yellowish-brown colour.
  • Habit: Elongated prismatic crystals, tabular massive, stalactitic or radiating fibrous.

Occurrence of Goethite:

Geothite is a secondary mineral. It is found in the oxidation zone of veins containing iron minerals. It is usaully formed by the oxidation of minerals, such as a siderite, pyrite and magnetite. Goethite is a principal constituent of limonite.

Uses of Goethite:

  • Goethite is used as a source of iron.
  • It can also be used as a clay-earth pigment.
  • Goethite has weak magnetite property, therefore it can also be used as magnetics.

(4). Siderite: FeCO3

Physical properties of Siderite:

  • Crystal System: hexagonal
  • Cleavage: perfect rhombohedral
  • Hardness: 3.5 -4.0 in Moh’s scale
  • Sp.Gr: 3.96
  • Lustre: vitreous
  • Colour: Light to dark brown.
  • Habit: Rhombohedral crystals, massive, fibrous, botryoidal or granular.

Occurrence of Sederite:

Massive siderite occurs as large sedimentary deposits. It also occurs as replacement deposits formed by the action of ferrous solution on limestones, siderite is also found in hydrothermal metallic veins.

Uses of Siderite:

  • Siderite is used as an iron ore.
  • It is also used for steal production.
  • Being brown in colour, it is also used as a brown pigment.

(5). Pyrite: Fe3S2

Physical properties of Pyrite:

  • Crystal System: cubic
  • Fracture: Conchoidal
  • Hardness: 6 – 6.5 in Moh’s scale
  • Sp.Gr: 5.2
  • Lustre: metallic
  • Colour: Brass yellow to golden.
  • Streak: Greenish or brownish-black.
  • Habit: Common forms are the cube which often shows striations. It is also found in massive, granular, and stalactitic habit.

Occurrence of Pyrite:

Pyrite is the most common sulfide mineral. It is found in hydrothermal veins, contact metamorphic deposits, and as an accessory mineral to sedimentary rocks. It is often associated with Chalcopyrite.

Uses of Pyrite:

  • It is used for the manufacturing of Sulfuric acid.
  • Pyrite is used to produce sulfur dioxide in paper industry.
  • Pyrite is most often mined for gold, copper, and other elements associated with it.
  • Pyrite, due to giving a golden colour, can be used instead of gold. It is, therefore, called false gold.
  • In old times, it was polished and used as a mirror.
  • It is also used to manufacture fertilizers, as it contains sulfur.

(6). Pyrhotite: FeS.Ni

Physical properties of Pyrhotite:

  • Crystal System: hexagonal
  • Cleavage: Absent
  • Fracture: Uneven
  • Hardness: 4 in Moh’s scale
  • Sp.Gr: 4.58 -4.65
  • Lustre: metallic
  • Colour: Bronze yellow tarnishing to brown.
  • Steak: Black
  • Special Character: Strongly magnetic.
  • Habit: Tabular crystals, massive or granular.

Occurrence of Pyrrhotite:

Pyrrhotite is formed by magmatic segregation in basic rocks. It is also found in high-temperature sulfide veins and replacement bodies.

Uses of Pyrrhotite:

  • As pyrrhotite contains a minor amount of nickel, therefore it is used as a source of nickel, which is a costly element, used in many types of batteries, electrically resistive magnets, and many other alloys.
  • Pyrrhotite is a good source of iron and sulfur.
  • It can be used to manufacture Sulfuric acid.
  • Pyrrhotite also contains a small quantity of Pentlandite, which is used as a catalyst to produce hydrogen and oxygen from water by the process of electrolysis.
  • Pentlandite is said to be as effective at this as platinum, which is significantly rarer and more expensive.

(7). Marcasite: FeS2

Physical properties of Marcasite:

  • Crystal System: orthorhombic
  • Cleavage: present
  • Hardness: 6 in Moh’s scale
  • Sp.Gr: 4.89
  • Lustre: metallic
  • Colour: pale bronze, yellow
  • Steak: Grayish black
  • Habit: Commonly found inTabular crystals, but occasionally it is also found in stalactitic, and radiating forms.

Occurrence of Marcasite:

It occurs as concretion in sedimentary rocks.

Uses of Marcasite:

  • It is a good source of Iron and Sulfur.
  • Uses as gemstone, and in jewellery.
  • Marcasite is used to attain concentration during a meditation (metaphysical importance).
  • In old times, Marcasite was used as medicine.

 

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