Banded iron formation
Also called: BIF · Topic: Minerals, Rocks and the Rock Cycle · NCERT: Beyond NCERT
Meaning
A banded iron formation (BIF) is an ancient sedimentary rock (rock built up in layers) with thin, alternating bands of iron oxide and silica. Most BIFs formed between 3.5 and 1.8 billion years ago. At that time, early life began photosynthesis and released oxygen into the sea. This oxygen reacted with iron dissolved in seawater, and the iron settled on the sea floor as iron oxide layers. BIFs hold most of the world's iron ore.
Example
India's richest iron ores come from BIFs of the Dharwar system. They include Bailadila in Chhattisgarh, Kudremukh in Karnataka and the Odisha–Jharkhand belt. In many places these rocks are now metamorphosed (changed by heat and pressure).
Don't confuse with
- Laterite: laterite is iron-rich soil formed today by heavy leaching (rain washing minerals out) in wet tropical areas. BIF is billions of years old and formed on the ancient sea floor.