Chapter 5 · Question 1
What are minerals and how do they occur in nature?
Answer
Direct Answer
Minerals are naturally occurring substances with a definite chemical composition and physical properties. They occur in igneous and metamorphic rocks as veins and lodes, in sedimentary rocks as beds and layers, through decomposition of surface rocks, and in alluvial deposits as placer minerals.
Simple Explanation
Minerals are natural substances with fixed chemical composition. They occur as veins in igneous rocks, layers in sedimentary rocks, surface residues, and placer deposits in alluvium.
Exam-Ready Structure
Minerals are naturally occurring substances with a definite chemical composition and distinct physical properties.
Modes of occurrence in nature:
1. In igneous and metamorphic rocks:
• Minerals occur as veins (small cracks) and lodes (larger cracks) formed when minerals in liquid or gaseous form rise through cracks and solidify.
• Examples: tin, copper, zinc, and lead are found in veins and lodes.
2. In sedimentary rocks:
• Minerals occur as beds (horizontal layers) and layers formed by deposition, accumulation, and concentration over long periods.
• Examples: coal, gypsum, potash, and some iron ores are found as beds and layers.
3. Through decomposition of surface rocks:
• Residual mass of weathered material contains minerals left behind after soluble components are washed away.
• Example: bauxite forms through the decomposition of rocks in tropical climates.
4. In alluvial deposits (placer deposits):
• Minerals that are not corroded by water, such as gold, platinum, and tin, are carried by rivers and deposited in sands and gravels of river beds and beaches.
• Example: gold in the sands of some Indian rivers.
Key Points
- Minerals are naturally occurring substances with a definite chemical composition and physical properties.
- They occur in igneous and metamorphic rocks as veins and lodes, in sedimentary rocks as beds and layers, through decomposition of surface rocks, and in alluvial deposits as placer minerals.
Answer Sources
- Meaning and occurrence of mineralstextbook section | Contemporary India-II | Minerals and Energy Resources | What is a mineral? | Pages 1-2