Rocks

Introduction

Minerals
The world is made from matter. Matter is anything that has mass and takes up space. The building blocks of matter are atoms. If matter is made up of just one kind of atom, it is called an element. If matter is made up of two or more elements, it is called a chemical compound. The periodic table is a compilation of all the known elements. Minerals are made up of these elements. Some minerals are made up of just one element. Most minerals contain two or more elements.

Minerals are (1) solid, (2) inorganic (not part of a plant or animal), (3) naturally-occurring (not man-made).

Minerals have an orderly structure. The atoms in minerals are arranged in a specific pattern that forms crystals. Gemstones are particularly beautiful crystals.

Rocks
All rocks are composed of minerals. Some rocks are made up of just one mineral, but most rocks contain several minerals that are joined together.

The difference between a rock and a mineral is like a cookie and the ingredients to make the cookie. Rocks are like your favorite tasty cookie. Minerals are like the ingredients to make the cookie: sugar, eggs, flour, butter, chocolate chips, etc.

The earth contains three main kinds of rocks: igneous, metamorphic, and sedimentary.

Igneous rocks are born in fire and heat. They are formed from magma which is free-flowing molten rock from deep within the earth. If the magma is brought to the surface of the earth through volcanic action or the movement of tectonic plates, it is then called lava. When this molten rock or lava cools and hardens, it is called extrusive igneous rock. If the magma cools just below the surface of the earth’s crust, it is called intrusive igneous rock.

Sedimentary rocks are valuable to geologists as they study the history of the earth because their layers are like a time capsule and often contain a record of millions of years of the earth’s history. Sediment from weathered and eroded rocks combine with bits and pieces of dead plants and animals and are deposited usually at the bottom of river, lakes, and oceans. When layers of sediment pile up on top of each other, the water is squeezed out of it, and the sediment becomes tightly packed or compressed. Minerals in sedimentary layers act like glue to hold the layers together. Over millions of years, these compacted layers join together to make sedimentary rock.

Metamorphic rocks are igneous and sedimentary rocks that through intense heat and pressure have been transformed or metamorphized. The intense heat changes the chemical composition of the original rock. The heat often comes from the rocks being pushed into the magma below the crust of the earth or from the rubbing and pushing against each other. The pressure often comes from movement of tectonic plates that squeeze rocks together.

Rock Cycle
The rock cycle has been shaping and changing the surface of the earth for millions of years. It is the process through which rocks are broken down and changed to create new rocks.

New igneous rocks are constantly being made, and old igneous rocks are constantly wearing down. New metamorphic and sedimentary rocks are also constantly forming and wearing down.

The cycle of new rock formation sometimes happens quickly as when a volcano oozes lava, and the lava cools within a few weeks to become igneous rocks. But most of the time, the rock cycle happens slowly over millions of years. This recycling of rock never stops.

Weathering/Erosion
Natural forces such as wind, water in the form of rain, water in the form of lake or ocean waves, the natural flow of water in rivers and streams, temperature changes, snow, ice, and the effect of plant and animal action cause rocks to weather or break down over time. These smaller, weathered pieces are called sediment.

Erosion is the movement of sediment from one place to another. This movement can be caused by wind, water, ice, and gravity. Weathering and erosion are both parts of the rock cycle.

Soil
Soil is as important to life on earth as are air and water. It’s where plants and crops grow that provide food for living things (including us!). It provides a home for countless numbers of living organisms. It plays a part in earth’s many biological and chemical cycles and helps to recycle the necessary nutrients for life.

It may not seem like it, but one of the biggest components of soil is rocks. Soil contains tiny particles of rock that have slowly broken down from larger pieces of rock. Depending on the size of the rock particles, soil can be categorized into sand, silt, and clay. Soil also contains tiny pieces of dead plants and animals; these tiny pieces are called organic matter and are important for healthy plant growth. Soil also contains air and water. The water in soil contains nutrients from rocks and minerals and organic matter. The roots of plants suck up the water from the soil and absorb the nutrients.

Decomposers help release nutrients from dead plants and animals into the soil, and these nutrients help plants grow. Decomposers include many kinds of insects, worms, snails, and microorganisms such as bacteria, fungi, and protozoa. They decompose (break down) dead plants and animals that are found in soil and help them rot which adds many of the necessary nutrients to the soil that plants need. All of these decomposed plants and animals break down into chemicals that plants can use again. The dead plants and animals basically get recycled into the soil.

Plants use light energy from the sun to conduct photosynthesis. They get hydrogen oxygen, and carbon from the air and water. From soil, plants absorb nutrients such as nitrogen, potassium, and phosphates, One of the byproducts of the rock cycle is the formation of soil. But it is a very slow process. Geologists believe that it takes from 500 to 1000 years to produce just one inch of topsoil.