Part.2 : Hydroxides

Brucite Mg(OH)₂

Composition
Fe²⁺ & limited Mn²⁺ may substitute for Mg

Occurrence
– In marble as alteration product after percales
– In serpentinite & chlorite schist, as small veins with talc, magnesite, & other Mg-bearing

Use In refractory materials

Crystal system Hexagonal (Trigonal)

Iron-Hydroxide (limonite)

Limonite: mixtures of Fe-(oxide & hydroxide)

Goethite: αFeO(OH)
– Most common of these minerals

limonite product by withering, hydrothermal alteration by break down of biotite, amphepal, pyroxine, magnitite, & iron-bearing minerals

Large masses of limonite produced by alteration & oxidation of pyrite FeS in hydrothermal sulfide deposits

Intense weathering of Fe-bearing rock result in formation of lateritic soil rich in Fe-hydroxide

Goethite are biomineral: found teeth of chitins, Microbial activity is almost certainly involved in their common

Aluminum Hydroxide (Bauxite)

Bauxite: mixed Al-hydroxide minerals

Bauxite produced in areas subjected to intense weathering, usually in tropical or semitropical climates, & contains clay (kaolin) & Fe-hydroxides

common minerals
gibbsite Al(OH)₃
diaspore αΑlO(OH)
bohmite γΑlO(OH)

found in deposits as withring or altration product of corundom, Al-silicates, & other Al-rich mineral

Manganese Oxide & Hydroxide (Wad)

Wad: materials that include substantial amounts of manganese oxide & hydroxide

Occurrence:
Hydrothermal Systems
Weathering & alteration of Mn bearing & other that contain Mn substituting for Fe-Mg
Some Mn deposits biologically mediated by Mn-oxidizing bacteria
Dendrites (precipitation by groundwater)

Most common minerals
Manganite MnO(OH)
Pyrolusite MnO₂