🌍 Chapter – 5
Minerals and Rocks (खनिज और शैलें)
🧩 Elements on Earth (पृथ्वी पर तत्त्व)
- Our Earth is made up of different types of elements (तत्व).
- These elements are found separately in the Earth’s crust (भूपर्पटी) as well as combined to form various substances (पदार्थ).
📌 98% of the Earth’s crust is made up of 8 elements:
- Oxygen (ऑक्सीजन)
- Silicon (सिलिकॉन)
- Aluminium (ऐल्यूमिनियम)
- Iron (लौह)
- Calcium (कैल्शियम)
- Sodium (सोडियम)
- Potassium (पोटैशियम)
- Magnesium (मैग्नीशियम)
➡️ Different types of minerals (खनिज) are formed by the combination of these elements, mainly due to the cooling of magma (मैग्मा का शीतलन).
⛏️ Minerals (खनिज)
- A mineral is a natural (प्राकृतिक) inorganic (अजैविक) substance with:✔️ Ordered atomic composition (सुसंगठित परमाण्विक संरचना)✔️ Definite chemical composition (निश्चित रासायनिक संघटन)✔️ Specific physical properties (विशिष्ट भौतिक गुण)
📌 About 2000 types of minerals have been identified in the Earth’s crust.
🔑 Some Major Minerals (प्रमुख खनिज)
1️⃣ Feldspar (फेल्डस्पार)
- Composed of silicon + oxygen.
- Makes up about 50% of the Earth’s crust.
- Colour: from light cream to pink.
- Uses: porcelain (चीनी मिट्टी) & glass making.
2️⃣ Quartz (क्वार्ट्ज़)
- Colour: white or colourless.
- Very hard (कठोर) & insoluble (अघुलनशील) in water.
- Uses: radio & radar instruments.
3️⃣ Pyroxene (पाय्रॉक्सीन)
- Constitutes about 10% of the Earth’s crust.
- Contains calcium, aluminium, magnesium, iron & silica.
- Common in meteorites (उल्कापिंड).
- Colour: green or black.
4️⃣ Mica (सिलिकेट खनिज)
- Found in about 4% of the Earth’s crust.
- Contains potassium, iron, aluminium, magnesium & silica.
- Uses: electrical equipment (विद्युत उपकरण).
- Found in igneous (अग्निज) & granite rocks (ग्रेनाइट शैल).
5️⃣ Amphibole (एम्फिबोल)
- Main elements: aluminium, calcium, silica, iron, magnesium.
- Constitutes about 7% of the Earth’s crust.
- Colour: green or black.
- Uses: asbestos industry (एस्बेस्टस उद्योग).
- Hornblende is also a type of amphibole.
6️⃣ Olivine (ओलिविन)
- Main elements: magnesium, iron & silica.
- Appears as green-coloured crystals (स्फटिक).
- Found in basaltic rocks (बेसाल्टिक शैल).
- Uses: jewellery (आभूषण).
🔹 Types of Minerals (खनिजों के प्रकार)
1️⃣ Metallic Minerals (धात्विक खनिज)
- These minerals contain traces of metals (धातु के अंश).
- They can be reused (पुनः प्रयोग) by melting.
- Divided into:
- Ferrous minerals (लौहधात्विक) → Iron, Manganese.
- Non-ferrous minerals (अलौहधात्विक) → Copper, Lead, Aluminium etc.
2️⃣ Non-Metallic Minerals (अधात्विक खनिज)
- Do not contain any metal content (धातु तत्व).
- Cannot be melted (गलाया नहीं जा सकता).
- Can be used only once.
- Examples: Sulphur (गंधक), Phosphate (फॉस्फेट), Nitrate (नाइट्रेट).
⚡ Factors Defining Physical Properties of Minerals
(खनिजों के भौतिक गुण व प्रकृति बताने वाले कारक)
- Outer appearance of the crystal (स्फटिक का बाहरी रूप)
- Withdrawal (निकर्षण)
- Cleavage/Partition (विदलन)
- Lustre/Glow (चमक)
- Colour (रंग)
- Transparency (पारदर्शिता)
- Hardness (कठोरता)
- Specific gravity / Relative load (सापेक्ष भार)
- Streak/Stripes (रेखाएं)
- Structure (संरचना)
🪨 Rocks (शैलें)
- The upper part of the Earth is made up of rocks (शैलें).
- Rocks are formed from one or more minerals (एक या अधिक खनिज).
- Range: From simple soil (साधारण मिट्टी) to hard rocks (कठोर शैलें).
🏔️ Types of Rocks (शैलों के प्रकार)
1️⃣ Igneous Rocks (अग्निज शैलें)
- Also called Primary rocks (प्राथमिक शैलें).
- Formed by cooling of lava & magma (लावा व मैग्मा के शीतलन से).
- Impermeable (अभेद्य) → water cannot pass through.
- No fossils (जीवाश्म नहीं मिलते).
- Examples: Granite (ग्रेनाइट), Gabbro (गैब्रो), Basalt (बेसाल्ट).
2️⃣ Sedimentary Rocks (अवसादी शैलें)
- Word Sediment (अवसाद) → Latin word meaning to settle.
- Formed by deposition (अवसादन) of materials by rivers, winds, glaciers.
📌 Classification:
- Mechanically formed (यांत्रिक रूप से निर्मित) → Sandstone, Limestone, Shale.
- Organically formed (जैविक रूप से निर्मित) → Chalk, Coal.
- Chemically formed (रासायनिक रूप से निर्मित) → Potash, Halite.
3️⃣ Metamorphic Rocks (रूपांतरित शैलें)
- Metamorphic = Change in form (रूप परिवर्तन).
- Formed by changes in pressure (दबाव), temperature (तापमान) & volume (आयतन).
- When sedimentary rocks are subjected to heat & pressure (due to plate movement / sliding) → they transform into new rocks.
- Example:
- Limestone → Marble
- Shale → Slate
- Coal → Graphite
🔥 Types of Metamorphism (रूपांतरण के प्रकार)
1️⃣ Dynamic Metamorphism (गतिशील रूपांतरण)
- Occurs due to breaking & grinding (टूटना और पीसना) of the original rocks.
- Rocks are re-formed (पुनः निर्मित) under mechanical forces.
2️⃣ Thermal Metamorphism (ऊष्मीय रूपांतरण)
- Involves chemical changes (रासायनिक परिवर्तन) & re-crystallization (पुनः स्फटीकरण) in parent rocks.
3️⃣ Territorial Metamorphism (क्षेत्रीय रूपांतरण)
- Takes place due to high temperature (उच्च तापमान) and high pressure (अत्यधिक दबाव).
- Affects rocks of large areas (विशाल क्षेत्र).
4️⃣ Contact Metamorphism (संपर्क रूपांतरण)
- Transformation occurs when rocks come in contact with hot lava (गर्म लावा से संपर्क).
🪨 Why are Igneous Rocks called Primary Rocks? (अग्निज शैलें प्राथमिक शैलें क्यों कहलाती हैं?)
- Igneous rocks are the oldest rocks (सबसे प्राचीन शैलें) on Earth.
- Initially, Earth’s surface had magma (लावा/मैग्मा) in molten form.
- By cooling & solidification (शीतलन और ठोसकरण) of magma → igneous rocks formed.
- They were the first rocks (प्रथम शैलें), hence called Primary rocks (प्राथमिक शैलें).
- Later, from these rocks, sedimentary (अवसादी) and metamorphic (रूपांतरित) rocks developed.
🎨 Banded Rocks (पट्टिकित शैलें)
- Sometimes minerals (खनिज) or particles (कण) are arranged in layers (परतें).
- They appear in light & dark colours (हल्के व गहरे रंग) alternately.
- Such formations in metamorphic rocks are called Banding (पट्टिकरण).
- Rocks showing this property are called Banded Rocks (पट्टिकित शैलें).
🔄 Rock Cycle (शैल चक्र)
- Igneous rocks (अग्निज शैलें) are formed first.
- Weathering & erosion convert them into sediments (अवसाद) → forming Sedimentary rocks (अवसादी शैलें).
- Under heat & pressure, Igneous + Sedimentary → Metamorphic rocks (रूपांतरित शैलें).
- At great depths, Sedimentary / Metamorphic rocks melt → back to Magma, forming new Igneous rocks.
📌 Definition:
👉 The continuous process of converting one type of rock into another is called the Rock Cycle (शैल चक्र).
➡️ It is a cyclical & continuous process (सतत एवं चक्रीय प्रक्रिया).
🏗️ Rock Building (शैल निर्माण)
- Erosion agents (अपक्षय कारक) like rivers & winds deposit weathered materials (अपक्षयित पदार्थ).
- Due to compression & pressure (दबाव व संपीड़न), these deposits harden into rocks.
- This process is called Rock Building (शैल निर्माण).
✍️ Foliation / Lineation (पत्रण / रेखांकन)
- During metamorphism, minerals (खनिज) of rocks get arranged in layers or lines (परतों या रेखाओं में).
- This alignment is called Foliation (पत्रण) or Lineation (रेखांकन).
