Rocks and Minerals

According to Webster’s Dictionary, the definition of a mineral is an inorganic substance. Citrine is one of the most popular minerals. It is a variety of quartz. Citrine is a yellowish-orange mineral. Citrine is a very popular gemstone because it is very affordable and very pretty. Along with topaz, citrine is the birthstone for the month of November and the anniversary gemstone for the 17th year of marriage ( Citrine is also considered a symbol of hope, youth, health, and fidelity ( In ancient times, citrine was carried as a protection against snake venom and evil thoughts ( Other names for citrine are Imperial Topaz, Oriental Topaz, and Precious Topaz.

A chemical formula is what elements make up the mineral (Feather & Snyder, 1999). These elements can be found on the periodic table. The chemical formula of citrine is SiO2, which is silicon and oxygen (

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According to Webster’s Dictionary, a silicate mineral is a combination of silicon, oxygen, and one or more minerals. Because citrine is made up of silicon and oxygen, it is a silicate mineral.

The properties you can observe without changing a substance into a new substance are physical properties (Feather & Snyder, 1999). The five main physical properties in minerals are hardness, cleavage, fracture, streak and luster.

Hardness is a measure of how easily a mineral can be scratched. Hardness is usually measured on Mohs hardness scale. The scale is measured from one to ten, with one being the softest and 10 being the hardness (Feather & Snyder, 1999). All kinds of quartz have a hardness of seven. Because citrine is in the quartz family, it has a hardness of seven (

Minerals that break along smooth flat surfaces have cleavage. Cleavage is determined by the arrangement of mineral’s atoms (Feather & Snyder, 1999). Citrine has no cleavage, therefore it has fracture. Minerals that break with rough or jagged edges have fracture. Citrine has fracture because it has no cleavage (Feather & Snyder, 1999).

The color of a mineral when it is broken up and powdered is called streak (Feather & Snyder, 1999). The streak of citrine is white.

Luster describes how light is reflected from a mineral’s surface (Feather & Snyder, 1999). The luster of citrine is vitreous, or closely resembles glass (

Citrine is found in most places but most miners and manufacturers go to Brazil to find it because of the quality and availability there (

Citrine is mostly used for jewelry but is also found in oscillators and timepieces for radios ( Citrine is also used a lot as a substitute for yellow sapphire and yellow diamond. Minerals are found in many kinds of rocks. In this next section, you will learn how minerals make up rocks, and how rocks are formed.

A rock is a mixture of minerals, mineraloids, glass, or organic matter (Feather & Snyder, 1999). Most people know what a rock is but they don’t know how it forms. The process of how rocks form is called the rock cycle. In this report, you will learn about the stages in the rock cycle and the three different types of rock in the rock cycle.

James Hutton came up with the rock cycle. Hutton is known as the eminent 18th century farmer and founder of modern geoscience ( Scientists all over the world are still using Hutton’s rock cycle today.

Igneous rocks are sometimes referred as fire rocks. They form under ground or above ground (Feather & Snyder, 1999). All igneous rocks are formed in the process of volcano formation ( Igneous rocks come in two forms, intrusive and extrusive.

Rocks that form below the earth’s surface are called intrusive rocks (Feather & Snyder, 1999). Intrusive rocks form when magma gets trapped in small pockets below the earth’s surface. As these pockets of magma cool, the magma becomes igneous rocks. (

Extrusive rocks are formed when lava from volcanoes cool on or near the earth’s surface

(Feather & Snyder, 1999). The lava cools because it is exposed to air and moisture. The air and moisture cause the rock to harden. The harden magma becomes rocks called extrusive rocks (Feather & Snyder, 1999). An example of an extrusive rock is rhyolite.

An example of a fine-grained, extrusive igneous rock is rhyolite. Rhyolite is an igneous rock because it forms from volcano eruptions. Rhyolite can look very different depending on how it erupts ( Rhyolite can be made up of many different colors ranging from dark gray to pink ( Special pieces of rhyolite will show a spider webbing design.

Rhyolite is very closely related to granite. The difference is rhyolite has much finer crystals. These crystals are so small that they cannot be seen by the naked eye. Rhyolite very rapidly which gives it a glassy appearance. The minerals that make up rhyolite are quartz, feldspar, mica, and hornblende. All of this information is according to

Rhyolite is found all over the world where there are volcanic mountains ( Certain colors of rhyolite are found in certain places, though. For example, certain kinds of red rhyolite are only found in California and parts of Nevada. This information is according to

Rhyolite has no uses because it is a volcanic rock. Some rock collectors think rhyolite is

valuable rock, though. An igneous rock is just one of three types of rocks. Another type of rock is a sedimentary rock.

Sediments are loose material such as rock fragments, mineral grains, and bits of plant and animal remains that have been moved by wind, water, ice, or gravity. These sediments form a rock called a sedimentary rock.

Rocks that form when sediments become pressed or cemented together are called sedimentary rocks (Feather & Snyder, 1999). Sedimentary rocks cover about 75% of the earth’s surface. Sedimentary rocks are usually classified by two kinds, detrial or chemical.

Rocks that are made from broken fragments or other rocks are called detrial rocks (Feather & Snyder, 1999). These broken fragments compact or cement together like all sedimentary rocks. Detrial rocks are often referred to as clastic rocks.

Detrial sedimentary rocks are often referred to as clastic rocks because of their texture. The word clastic comes from the Greek word meaning “broken” (Feather & Snyder, 1999). Clastic rocks are from solid grain unlike chemical sedimentary rocks ( Examples of clastic rocks are sandstone and shale.

Rocks that form from minerals precipitating out of water are called chemical sedimentary rocks. The deposits of minerals that remain after evaporation harden, and form chemical sedimentary rocks. An example of a chemical sedimentary rock is limestone.

Limestone is a fine-grained, chemical sedimentary rock. It is a sedimentary rock because it forms from sediments being pressed or cemented together (Feather & Snyder, 1999). Most limestone is gray but all colors of limestone from white to black have been found ( It commonly contains fossils such as shells or other animal remains. In some cases, the fossils make up most of the rock (

Limestone is mostly made up of the mineral calcite. The other minerals in limestone can differ greatly because it is found in a lot of environments. Examples of these other minerals are dolomite and aragonite.

Limestone is found all over the world but the most common form of limestone is found in marine environments.

Limestone makes an excellent building stone because it can be carved easily. It can be cut any way without splitting. Limestone is especially good for foundations and walls where a high polish is not needed. Limestone is also used in concrete. Some factories use limestone to clean waste gases and water before releasing them into the environment. I have completed telling you about igneous and sedimentary rocks. Next, I will tell you about the 3rd and final type of rock, metamorphic rocks.

Metamorphic rocks are formed by action of pressure, temperature, and fluids. When rocks are deeply buried into the earth, they can deform. New minerals crystallize on them to form metamorphic rocks ( The two kinds of metamorphic rocks are foliated and non-foliated.

When mineral grains flatten and line up in parallel bands, it is called a foliated rock (Feather & Snyder, 1999). Foliated rocks look like stepping-stones or stair steps. They are arranged into layers when they are exposed to heat and pressure unlike non-foliated rocks.

Metamorphic rocks where no banding occurs are called non-foliated rocks. Minerals inside the rocks change, grow, and rearrange, but they don’t band together like foliated rocks (Feather & Snyder, 1999). One example of a non-foliated rock is marble.

Marble is a non-foliated metamorphic rock. Marble is a rock formed by the metamorphism of limestone. Marble can be a variety of colors depending on various impurities. Marble is always distinguished by being softer than glass. (

Marble is primarily composed of the mineral calcite ( Some marble has variations of minerals. The variations give marble a wide variety of colors (

Marble is found in many countries, including Belgium, France, Greece, India, Italy, Spain, and the United Kingdom. Some South American nations also have some marble. In the United States, Georgia produces the most marble. Other marble producing states include Alabama, Colorado, Montana, Tennessee, Texas, and Vermont (

Marble has been highly valued for its beauty, strength, and resistance to fire and erosion. The ancient Greeks used marble in many buildings and statues and it is still being used today in floors and other parts of buildings. Smaller pieces of marble are crushed and used as abrasives in soaps. Crushed marble is also used in paving roads and in roofing materials ( That concludes the three types of rocks. Now you will learn about the process of the rock cycle.

Molten rock material solidifies at depth or at the earth’s surface to form igneous rocks.

Uplift and exposure of rocks at the earth’s surface destabilizes the mineral structures.

The minerals break down into smaller grains, which are transported and deposited as

sediments. The sediments or compacted and cemented and sedimentary rocks are

formed. Changes in temperature and pressure can allow igneous and sedimentary

rocks to change physically or chemically to form metamorphic rocks. At higher

temperatures, metamorphic rocks may be partially melted, and crystallization of

this melt will create igneous rocks. Uplift and erosion can expose all rocks types at the

surface, re-initializing the cycle (

This Diagram was drawn by Fallan Davis from

None (Sources are sited)

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