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Iron Minerals in Sedimentary Envmt (Siderite (Muddy rocks…
Iron Minerals in Sedimentary Envmt
MOST IMPORTANT
haematite (Fe oxide - most common)
magnetite
limonite (rust)
chamosite (Fe silicate)
siderite (Fe carbonate)
pyrite
Haematite
Iron 3 oxide
Most common Fe mineral?
Magnetite
Fe3O4
Not v common
Limonite
iron oxide with water in structure
very common - rust
Fe(OH).nH20
Chamosite
Hydrous aluminium silicate of iron
often oolitic or cryptocrystalline mud
large tabular crystal sometimes
alteration to siderite is common
(esp as rim)
Glauconite
silicate rich in Fe, K, Mn
occurs as grains / pellets
green pleochroic
Siderite
Iron 3 carbonate - FeCO3
Fresh ferric rock surfaces may weather to siderite
Muddy rocks
anhedral/lozenge crystals
often opaque cores
Spherulites
circular outline with thin fibrous filling
Cement
anhedral aggregates
euhedral void fillings
Alteration
replaces grains i.e. chamosite ooids
Pyrite
Kaolinite
clay mineral
DOES NOT CONTAIN Fe
occurs alongside Fe mins often