1310-14-1

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Questions And Answer

• Description

  Goethite is typically formed under oxidizing conditions as a weathering product of femferous minerals, siderite, pyrite, and magnetite, and is widespread as deposits in bogs. It is commonly associated with hematite, pyrolusite, manganite, calcite, quartz, lepidocrocite, clay minerals, and limonite. Hydrous iron oxide is also called limonite. By x-ray examination, most limonites are actually cryptocrystalline goethite with absorbed or capillary water (Palache, Berman, and Frondel 1944). Several excellent pigment ore sources are found in India. Domestic ochre is mined in Georgia and Virginia.;

• Physicochemical properties

  Chemical formula	αFeOOH.xH20
  Chemical composition of ore	50% to 88% Fe203, 9% to 10% H20, balance silicate or clay minerals
  Crystal class	Orthorhombic; dipyramidal
  Habit	Prismatic and striated; also in tablets or scales, grading into acicular and long prismatic forms; also earthy
  Physical	Cleavage [010] perfect, [100] less so, fracture uneven, hardness of 5.0-5.5
  Reaction mechanisms	Will form ferrites through solid-state reactions as noted under hemotite. Can also be converted from αFeOOH.xH20 to αFesO3 by heat and to ferromagnetic γfe2O3 by reduction and oxidation.
  Melting point	Decomposes; naturals (finely ground) start to dehydroxylate at 190°C and is essentially dehydroxylated at 320°C; synthetics start at 180°C and are completely dehydroxylated at 300°C
  Boiling point	Decomposes
  Solubility	Considered insoluble in water and common organic solvents, 0.0015 gpl cold water
  Index of refraction	2.26-2.27
  Specific gravity	3.3-4.0
  Magnetic	Antiferromagnetic

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