Chapter 8 : Rocks and Minerals
A rock is defined as a solid mass that is naturally occurring and consisting of one or more minerals.
Rocks can be hard or soft, as small as a grain or as large as a building
Rocks are generally made up of two or more minerals, but minerals are not made of rocks.
Earth’s crust and part of its covering are made of rock.
Rocks have property of hardness, color, and texture.
Topics covered in this snack-sized chapter:
Rocks are divided in different categories based on their origination.
Rocks formed in different environments have different characters
Sand is also a type of rock.
Igneous Rocks are formed from cooling and crystallization of molten rock- magma.
Igneous Rocks make the outer layer of earth.
Igneous Rocks are formed when molten rock cools and solidify.
- Magma- It is molten rocks within the Earth’s Surface.
Most important content of igneous rocks is Magma which is inside the earth crust.
Characteristics of Magma:
- Igneous rocks are made of magma.
- Form from particles melting from rocks.
Rocks formed from lava are extrusive, and generally called as volcanic rocks.
Sedimentary rocks are formed by decomposition of material at Earth surface and within water bodies.
Due to action of wind, water, gravity, thermal expansion, rocks are divided into small pieces of rocks that are called Sedimentary Rocks.
Particles that form a sedimentary rock by accumulating are called sediment.
Clastic: This is made up of broken up particles.
Chemical/Biochemical: These types of sedimentary rocks are formed by decomposition of organic material.
Weathering breaks down rocks into finer material that further decompose as sediments.
The process of compaction and cementation of these sediments over long period of time turn sediments into rocks, these are sedimentary rocks
Metamorphic rocks are those which change themselves under high pressure and temperature.
Metamorphic is derived from word metamorphism which means the process of “change in forms”.
Changes in these rocks occurred due to chemical reaction between minerals in the rock.
The chemical reaction is entirely in its solid state as in igneous rocks (changes occur in its molten state).
These rocks are created by high pressure and heat and by some chemical reactions.
Metamorphic rocks are formed by other rocks through metamorphism process.
- Magma at surface is called lava.
- It starts from low grade to high grade.
- During this process rock remain essentially strong.
- New material from preexisting minerals formed through recrystallization.
Weathering is a process of breaking down rocks.
It is disintegration, or breakdown of rock material.
It allows new rocks to be formed over millions of years and then they emerge from the sea.
Soil also gains its fertility due to weathering.
There are basically two types of weathering:
- Deformation of existing minerals, change in shape and internal property.
In Mechanical weathering rocks break physically into small pieces.
In this process rocks break atom by atom, water plays the most important role in chemical weathering.
Rock cycle is a group of changes in different types of rocks.
Igneous rock changes into sedimentary or metamorphic rock.
Sedimentary rock can change into metamorphic rock or into igneous rock.
Likewise metamorphic rock can change into igneous or sedimentary rock.
Igneous rocks are made of molten lava and when it cools down we get our rock
Through wind, small particles of sediments move from one place to another, which forms earth layers that make sedimentary rocks and likewise the cycle continuous.
A mineral is a naturally occurring substance that is solid and stable at room temperature
It is representable by a chemical formula, usually a biogenic, and has an ordered atomic structure
The earth is made up of rocks, which are in turn made of minerals.
Minerals are the “building blocks” of rocks.
Five basic properties of minerals are as follow:
- Not previously living (inorganic)
- Definite chemical composition
Minerals are classified on the basis of:
- Orderly internal atomic arrangement
- Chemical composition (what elements they are composed of)
Minerals are made of different ions
Ions are charged particles
- Crystal structure (how the elements are arranged)
- Cations are positively charged.
Geologists determine the identity of an unknown mineral by describing its physical properties.
Every mineral have their own unique set of physical properties and characteristics.
Luster- Refers to the light reflected off of the mineral.
Minerals can be termed: glassy, opaque, transparent, shiny.
One of the first determinations a geologist must make is whether the mineral in metallic or non-metallic.
Habitat- Distinctive shape of the way the mineral commonly (habitually) appears.
Minerals vary greatly in color and thus color is unreliable as a physical property in many minerals, e.g. quartz
Hardness - The ability to resist abrasion or scratching.
Crystal structure -Crystal structure depends on sizes of and charges on ions.
Metallic minerals: Minerals like gold, iron, copper are metallic they have all the properties of metal.
Metals: They are good conductors of heat and electricity, hard, lustrous, high melting and boiling point, etc.
All these properties are satisfied by metallic minerals.
Non Metallic minerals: Minerals like Quartz and Diamond are nonmetallic they have all the properties of nonmetals.
Nonmetals: They are not good conductors of heat and electricity and do not possess very high melting and boiling point.
These properties are for all nonmetallic minerals.
Minerals are found in the form of ores beneath the earth.
The ores must be processed to extract the metals of interest from the waste rock and from the ore minerals.
Commercially valuable minerals and rocks are referred to as industrial minerals.
Our food contains minerals, which is necessary for our body to be fit.
The most common mineral that is used in our food regularly is salt (NaCl).
The study of minerals is called mineralogy.
A mineral is sometimes made up of just one chemical element but more often it is a compound (mixture) of two or more.
For example, diamonds are made up of just carbon, while fluorite is made up of a compound of calcium and fluorine.
- Anions are negatively charged.