Minerals and Rocks ESS

🧱 What Is a Mineral?

A mineral is a naturally occurring, inorganic solid with a definite chemical composition and an ordered internal structure. This means minerals are formed through geological processes, have consistent chemical formulas, and possess a crystalline structure.

Key Characteristics:

• Naturally Occurring: Formed by natural geological processes.
  
  

• Inorganic: Not made by biological organisms.
  
  

• Solid: Maintains a definite shape and volume.
  
  

• Definite Chemical Composition: Consists of specific elements in fixed proportions.
  
  

• Crystalline Structure: Atoms are arranged in an orderly, repeating pattern.​
  
  

💎 Why Are Only a Few Minerals So Common?

As of March 2025 the International Mineralogical Association has recognized 6,126 valid minerals, only a relatively small group (about 20-30) are considered "common rock-forming minerals". These few dominate Earth's crust because:

• 🌡 They form under a wide range of temperature and pressure conditions.
  
  

• 🌋 They are composed of the most abundant elements in the Earth's crust—primarily oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg).
  
  

🔬 Mineral Identification Techniques

Physical Properties (NYS Regents Standard 3.1): Minerals can be identified based on their physical properties:

• Hardness: Resistance to scratching, measured by the Mohs scale.
  
  

• Luster: Appearance of the mineral's surface in reflected light (e.g., metallic or non-metallic).
  
  

• Streak: Color of the mineral's powder when rubbed on a porcelain plate.
  
  

• Cleavage and Fracture: How a mineral breaks—along flat planes (cleavage) or irregular surfaces (fracture).
  
  

• Color: Visible hue, though it can vary due to impurities. (LEAST HELPFUL)
  
  

🌋 Formation of Minerals

Processes (NYS Regents Standard 3.1): Minerals form through various geological processes:

• Crystallization from Magma or Lava: As molten rock cools, minerals crystallize.
  
  

• Precipitation: Minerals precipitate from solutions due to evaporation or chemical changes.
  
  

• Biological Activity: Organisms can produce minerals (e.g., calcite in shells).​
  
  

🪨 Rock Cycle

Rock Formation (NYS Regents Standard 3.1): Minerals are the building blocks of rocks. Depending on their formation, rocks are classified as:

• Igneous Rocks: Formed from the solidification of molten material.

• Sedimentary Rocks: Formed from the compaction and cementation of sediments.

• Metamorphic Rocks: Formed from existing rocks transformed by heat and pressure.​

🪨 Rocks Overview

Rocks are classified by how they form. The three main types are:

🟤 Sedimentary Rocks

➤ Formation:

• Formed from the compaction and cementation of sediments.

  • Where do these sediments come from?

    • Erosion & deposition

• Can also form by 

  • evaporation (e.g., rock salt)

  • organic processes (e.g., coal).
    
    

➤ Characteristics:

• Often have layers (strata).
  
  

• May contain fossils.
  
  

• Usually clastic (made of fragments) or chemical/organic.
  
  

➤ Textures:

• Clastic: made of fragments, classified by grain size
  
  

• Crystalline: formed by evaporation/precipitation
  
  

• Bioclastic: formed from organic remains
  
  

➤ Examples:

• Conglomerate: rounded pebbles cemented together
  
  

• Sandstone: sand-sized particles
  
  

• Limestone: often bioclastic; can contain fossils
  
  

• Shale: fine-grained
  
  

🔴 Igneous Rocks

➤ Formation:

• Formed from cooling and solidification of magma or lava.
  
  

➤ Texture:

• Intrusive (plutonic): cool slowly inside Earth → large crystals
  
  

• Extrusive (volcanic): cool quickly on surface → small or no crystals
  
  

➤ Crystal Size vs Cooling Rate:

• Longer cooling → larger crystals
  
  

• Shorter cooling → smaller crystals
  
  

➤ Common Features:

• Glassy or vesicular texture (from gas bubbles)

  • Extrusive

• Lack fossils

• Felsic vs Mafic

  • 
    
    

➤ Examples:

• Granite: coarse-grained, light-colored, intrusive
  
  

• Basalt: fine-grained, dark-colored, extrusive
  
  

• Rhyolite: fine-grained, high in silica
  
  

• Scoria/Pumice: vesicular (gas pockets), extrusive
  
  

⚫ Metamorphic Rocks

➤ Formation:

• Formed by heat and pressure acting on other rocks (no melting).
  
  

• Contact metamorphism = heat from magma
  
  

• Regional metamorphism = pressure from tectonic activity
  
  

➤ Textures:

• Foliated: banded or layered (e.g., schist, gneiss)
  
  

• Non-foliated: no visible layers (e.g., marble, quartzite)
  
  

➤ Characteristics:

• May show distorted or banded structure
  
  

• Recrystallization of minerals
  
  

• No fossils
  
  

➤ Rock Progressions:

• Shale → Slate → Phyllite → Schist → Gneiss
  
  

• Limestone → Marble
  
  

• Sandstone → Quartzite
  
  

➤ Examples:

• Schist: foliated, visible mica crystals
  
  

• Gneiss: banded, coarse-grained
  
  

• Marble: non-foliated, from limestone
  
  

• Quartzite: non-foliated, from sandstone