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Hi my name is Ciara and I’m here to talk to you about minerals, the three main rock types and how they are interrelated.

Let’s begin with minerals.

What is a mineral?

By definition, a mineral is a naturally-occurring, inorganic crystalline solid that has an orderly and repeating atomic structure. All minerals must be solid, natural, and inorganic (meaning they grew without the influence of plants and animals).

Minerals are composed of atoms of one or more elements. The most common minerals are made up of oxygen, silicon, aluminum, and iron, which are the four most abundant elements in the earth’s crust.

Some common minerals you might be familiar with are gypsum and halite.

Gypsum (Calcium Sulfate Dihydrate)

http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Gypsum.html

Halite (Sodium Chloride)

http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Halite.html

Minerals have unique physical and chemical properties that allow us to distinguish one from another. These include optical properties like luster, ability to transmit light, color, and streak. Other physical properties include crystal shape, mineral strength, tenacity, hardness, cleavage and fracture. Density and specific gravity are also other important properties of minerals.

So what is the relationship between minerals and rocks and how are they different?

Well, minerals are the building blocks of rocks. Rocks are composed of naturally occurring minerals and/or mineral-like matter, like glass or organic matter.

Let’s begin with igneous rocks. Igneous rocks are rocks that crystallize from molten material and are classified based upon where they cooled within the earth’s crust. In other words, the cooling rate of the molten material ultimately determines the grain texture of the rock.

Factors that control the cooling rate of molten depend on depth in the earth’s crust, shape and size of magma body, and the presence of groundwater passing through magma.

There are two main types of igneous rocks: extrusive and intrusive. Extrusive igneous rocks solidify from lava and are fine-grained. Examples include basalt, andesite, and rhyolite. They are fine grained because they cool much faster than intrusive rocks.

Basalt

Andesite

Rhyolite

Intrusive igneous rocks are rocks that form from molten magma and cool underground. The slow cooling underground allows the minerals to possess a coarse-grained texture. Examples include granite and diorite.

Granite

Diorite

The second rock type is sedimentary. Sedimentary rocks are the most common type of rock at Earth’s surface. These rocks form from the erosion and subsequent deposition of pre-existing rocks.

The formation of a sedimentary rock begins when weathering and erosive processes loosen pieces of pre-existing bedrock over time (thousands of years) and are then transported by gravity, wind, water, or ice.

http://geologylearn.blogspot.com/2015/11/classes-of-sedimentary-rocks.html

The loose sediment eventually turns into solid rock through two main processes: lithification and cementation. During lithification, sediment is compacted through burial and the overlying material squeezes water and air out between the clasts. Cementation occurs when the spaces between compacted sediment clasts are filled with minerals (like quartz or calcite) that precipitate from groundwater. This cement acts like glue and holds the grains together. Examples of sedimentary rocks include shale, sandstone, limestone, and conglomerate.

Shale

Sandstone

Limestone

Conglomerate

The third type of rock is metamorphic. A metamorphic rock is any rock (igneous or sedimentary) that has been altered by heat, pressure, and/or the chemical action of fluids. This process of change is called metamorphism. Geologists separate metamorphic rocks into two classes: foliated and non-foliated. Foliated metamorphic rocks have alternating dark and light layers that can be distinguished from one another based on their composition, grain size, and the nature of their foliation. Examples of foliated metamorphic rocks include gneiss, phyllite, schist, and slate. Examples of non-foliated metamorphic rocks include marble, hornfels, quartzite, and novaculite.

Gneiss

Phyllite

Schist

Slate

Marble

Hornfels

Quartzite

The three basic rock types are all interrelated. Over long time spans, these rocks are constantly changing and transforming from one type to another. This is referred to as the rock cycle.

http://science.cc.uwf.edu/sh/curr/rockcyc/rockcyc.htm

Thanks for stopping by!