Minerals are substances that are formed in nature which are inorganic (non-living), crystalline solids. The earth is made of minerals. Unlike rocks, which are made of 2 or more minerals, every part of a particular mineral has the same physical properties as the rest of the piece. Each mineral has its own chemical composition and its own crystal structure.

A crystal forms when the atoms of a mineral line up in a regular pattern. If the crystal grows in an undisturbed open cavity, the atoms continue to line up until smooth faces form on the surfaces. This can happen in places such as a gas bubble from a volcanic eruption, forming a geode. There are many different shapes of crystals, depending upon the type of mineral. calcite garnet quartz gypsum

 

tourmaline pyrite ruby sulfur

geodes

 

 

 

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Properties of Minerals

Minerals are identified by their properties. Scientists use many different tests, including the ones we use in class. We will be looking at the following properties:

Color - Some minerals can be found in many different colors. What you see when you look at it is called observable color. This doesn't really help identify a mineral. To be sure you are properly identifying a mineral by color, a streak test is done. The mineral is rubbed on a piece of white porcelain to produce the mineral's identifying color. When we write with a pencil the graphite leaves a dark streak on the paper!

Light Transmissivity - The light test is done to see how much light shines through a sample of the mineral. If no light goes through, it is opaque. If some light shines through, it is called translucent. If almost all the light shines through, it is called transparent.

Luster - A mineral's luster, or shine, depends on the way its surface reflects light. Minerals can be metallic, dull, waxy, glassy or pearly.

Hardness - The hardness of a mineral is related to how easy it is to scratch. Minerals are classified using the Mohs scale. The softest minerals can be scratched by a fingernail. Copper pennies or glass can be used to scratch medium-hard minerals. Steel must be used to scratch the harder minerals. Diamond is the hardest, and can only be scratched by another diamond.

Magnetism - Most minerals are not attracted to a magnet. Magnetite and lodestone are natural magnets that have been used for centuries due to their magnetic property.

Scientists use other tests to identify minerals by their properties. Some of the other tests include:

Cleavage - Cleavage is how a mineral breaks when hit with a sharp blow. Cleavage can be called perfect, good, fair or poor depending upon the smoothness of the break and the luster of the surface. Mica has good cleavage, as it splits into sheets.

Fracture - When a mineral breaks unevenly with no cleavage, the kind of break is called the fracture. Obsidian has a glass-like conchoidal fracture which made it great for ancient cultures to use it to make cutting tools and arrowheads.

Solubility in acids - Some minerals are very soluble in certain types of acids. Some do not react at all, or only react a little bit.

Pyroelectricity - When heated, some minerals such as tourmaline will become polarized and attract bits of paper to the ends.

Piezoelectricity - Some crystals vibrate when an electric current is applied to them. Electronic devices such as computers and watches make use of quartz crystals because of the piezoelectric vibrations.

Radioactivity - Some minerals are radioactive. Radioactivity can be detected by a Geiger counter or if it turns photographic film black. Special handling and shielding must be used for these minerals.

Luminescence - Some minerals shine brightly with a different color when they are in ultraviolet light.

 

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Gems and Birthstones

Many people attribute certain gems to each month of the year. Each gem also has certain characteristics that people believe are in the stone. Here is a list of the birthstones for each month:

Month	Gem or Gems	Characteristics
January	Garnet	Constancy
February	Amethyst	Sincerity
March	Aquamarine or Bloodstone	Courage
April	Diamond	Innocence
May	Emerald	Love
June	Pearl, Moonstone or Alexandrite	Health
July	Ruby	Contentment
August	Peridot or Sardonyx	Married happiness
September	Sapphire	Clear thinking
October	Tourmaline or Opal	Hope
November	Topaz	Faithfulness
December	Turquoise or Zircon	Wealth

 

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Rocks are made up of a combination of 2 or more minerals. Rocks can be found everywhere in the world. They can be very different from one another and can have different properties. The properties of the rocks can give you clues about how the rocks were formed.

Some rocks form under water. They are made of bits of sand, clay, mud or shell that settled in layers. After a long time, the layers piled up and pressure caused them to stick together. Because these rocks are formed from bits of matter called sediment, they are called sedimentary rocks. If plants, bones or sea shells got into the layers, fossils formed.

 

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Igneous Rocks

Some rocks form underground. They form deep inside the earth where the rock is melted. The melted rock, called magma, erupts through cracks in the surface of the earth. When this happens, the melted rock is called lava. When the lava cools fast, the rocks are smooth and look like glass. When the lava cools slowly, gas bubbles form and the surfaced of the rock is rough. Sometimes the magma cools underground. These rocks are hard and heavy, and you can see pieces of minerals in them. All of these rocks that form from magma are called igneous rocks.

  Igneous rocks can form underground. (The magma is shown in green.)

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Metamorphic Rocks

Some rocks change due to movement of the earth. Earthquakes can move them, twist them, or break them up. Tremendous underground pressure can move the rocks. The heat of the earth can also change rocks. When rocks are changed by heat or pressure, they are called metamorphic rocks.

 

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Link to Rocks and Minerals Hotlist

 

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