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The Oxides These are more common minerals than sulfides and metal oxides are prized because of their economic value. These minerals are the source of many metals we use today. They are often found where metallic ores have been oxidized or rusted. These minerals must be refined to separate the metal from the oxygen, however it is far easier and far less polluting to refine oxides than sulfides. Oxides can be sub-metallic or non-metallic lustre, have fairly high specific gravity (heavy) and should be streaked if they are sub-metallic Remember to streak all sub-metallic minerals Have a magnet handy as the oxide Magnetite is magnetic. Remember to wash your hands after handling, due to the presence of heavy metals. PROPERTY Colour 3 very different possible forms: • Red massive “common iron rust” coloured masses • Deep red ,sub-metallic, hard botryoidal masses • Silvery metallic blades with a reddish rust. Crystal Form Bladed metallic crystals, botryoidal masses Cleavage/Fracture rare Lustre Massive (earthy), botryoidal and metallic blades. Hardness Botryoidal and metallic form is surprisingly hard (6) Specific Gravity heavy Streak Always reddish-brown (rust coloured) Other It is a major ore of iron (used to make steel). You can piles of at steel plants in Hamilton. PROPERTY Colour Black Crystal Form Often massive, but it is commonly found in octahedral crystals Cleavage/Fracture 4 directions – hard to see Lustre Sub-metallic Hardness Very hard (7) – can scratch glass – unusual for a sub-metallic mineral Specific Gravity Medium-heavy Streak black Other Magnetic Another common iron ore. Actual formula Fe2+Fe3+2O4 (spinel group) Same crystal structure as chromite and can easily be confused with chromite. PROPERTY Colour Gun-metal grey Crystal Form Common (cubes, pyritohedrons, striated crystals) but is usually seen massive Cleavage/Fracture Perfect in 3 directions 90˚ creating cubic cleavage fragments Lustre Metallic – very lustrous cleavage faces Hardness Very Hard (9) – scratches glass Specific Gravity Very heavy due to the lead – densest mineral in our set. Streak black Other Commonly associated with sphalerite. Galena “rusts” to a duller grey Non-magnetic It is the main ore of lead in the world PROPERTY Colour Yellow-gold – the colour is more yellow than pyrite but less golden than gold. Crystal Form Almost always massive Cleavage/Fracture none Lustre Metallic Hardness hard (4.5) – cannot scratch glass – can be scratched with a nail Specific Gravity Medium-heavy Streak black Other Non-magnetic The problem is that it is often associated with pyrrhotite which is magnetic It is a major ore of copper. Used for wiring and pipes.