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Cassiterite, Hematite, Magnetite, Goethite, Cuprite, Rutile,












Cassiterite: Tin Oxide 
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Cassiterite (SnO2)
 


Crystals are usually stubby/prismatic in habit with ocassional long pyramidal ends. 
Colour ranges
 from dark brown to black with a a high degree of sparkle (adamantine). Hardness ranges from
 6-7 with a  prismatic cleavage present. Cassiterite is common in high temperature hydrothermal
 veins with quartz and within or 
near to granites (pegmatites and greisens (altered granite)). World
 class 
deposits have been found in England (Cornwall), Malaysia, Russia and 
the USA.


Uses: Cassiterite is the main ore of tin.











Hematite: Iron Oxide 
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 Hematite (Fe2O3)
 

Colour ranges from steel-grey, black to bright red with the lustre either metallic, dull or earthy. 
Hematite crystals can be tabular or rhombohedral arranged in a rose like form (iron roses),
 or more commonly they are mammilated or botryoidal. Hardness ranges from 5-6. The most
 diagnostic feature of hematite is its streak which is always a dark red to red brown. Hematite
 is a common accessory mineral of many igneous rocks because it forms under oxidising conditions. Also present in pegmatites, hydrothermal veins and sedimentary rocks where it forms through the diagenesis of limonite often as ooliths or cement. World class deposits in USA (Lake Superior), Canada (Quebec), Venezuela and Brazil.   



Uses: Hematite is an important iron ore.











Magnetite: Iron Oxide 
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Magnetite (Fe3O4)
  


Magnetite crystals are black in colour with a metallic or sometimes dull lustre. Crystals can form
 perfect octahedrons or less commonly dodecahedrans, all with striated faces. Hardness ranges
 from 5.5-6.5 with no cleavage. One other important charactersitic of magnetite is that it is strongly magnetic. This mineral is common in a wide variety of rock types. In igneous mafic and ultramafic extrusives where it is present as an accessory mineral, in metamorphic rocks where it forms by the reduction of hematite and in detrital sediments and iron formations. World class deposits are found
 in Sweden (Kiruna district), South Africa (Bushveld Complex), USA (Utah), former USSR (Ural mountains).


Uses: This is the richest and most important ore of iron.












Goethite: Iron Hydroxide 
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Goethite FeO(OH)
  

Goethite is usually a dark brown colour but can be yellow when fine grained. Lustre is
 adamantine when crystalline but silky when massive. Crystals are more commonly tabular,
 acicular, botryoidal or massive in habit, prismatic crystals do exist but these are rare. Goethite has
 one perfect cleavage and a hardness of between 5-5.5. This mineral is an important constituent of limonite which is a rock that forms under oxidising conditions by replacing iron bearing minerals.
 World class deposits found in Cuba, Westphalia (Germany), Cornwall (England) and Labrador (Canada).


Uses: An important ore of iron.












Cuprite: Copper Oxide 
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Cuprite Cu2O
  

Cuprite is red to dark red in colour but can be altered to green malachite on the surface. The lustre varies from submetallic, adamantine or earthy. Crystals can be octahedral, cubic or dodecahedral but fine, acicular aggregates do exist. Cuprite has a hardness of between 3.5-4 and a poor cleavage. Cuprite is a common mineral in the oxidised zones of copper deposits associated with malachite, azurite, chalcocite and native copper. World class deposits have been found in France (Chessy), England (Cornwall), USA (Bisbee) and Chile (Chuquicamata).


Uses: An important ore of copper. Can also be cut into gemstones.












Rutile: Titanium Oxide 
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Rutile TiO2
  

Rutile varies in colour from yellow, red, brown or black with an adamantine lustre. Crystals can be stubby and prismatic but also needle-like with vertical straitions. Hardness is between 6 and 6.5 with a distinct prismatic cleavage. Rutile is a common accessory mineral in intrusive rocks and metamorphic rocks (gneisses, schists) and in the quartz veins running through them. It also occurs as a detrital mineral in sands, clays and shales. World class deposits have been found in fissures in the Swiss Alps, USA (Graves Mountain, Georgia and Nelson County, Virginia), Norway and Australia.



Uses: An important ore of titanium.








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