8Th Grade Earth Science Minerals Packet

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Minerals

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Minerals are all around us. Nearly every single thing we use is made of, or contains, minerals.

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What is a Mineral made of and what things are minerals a part of?

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atoms→molecules→elements,compounds→minerals→rocks

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Mineral Facts

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Minerals are naturally occurring, inorganic solids with fixed chemical compositions and an orderly arrangement of internal atoms.

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Defining Characteristics of Minerals

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1. Minerals are naturally occuring- This means that minerals are formed as a result of natural processes in or on Earth. Although scientist may have found ways to make similar materials in a lab, the manufactured materials are not minerals. Therefore, diamonds that are mined from Earth are minerals; diamonds that are manufactured are not minerals.

2. Minerals are inorganic- This means that minerals are formed by physical processes, not by biological processes. Although coal may at first seem to be a mineral because it was formed by natural processes, the carbon material that forms the coal comes from organisms like plants and animals that were once alive. Coal is not a mineral.

3. Minerals are solids- Solids have a definite shape and volume, while liquids and gasses take the shape of the container in which they are placed. Minerals are not called minerals unless they are in a solid state.

4. Minerals have fixed chemical compositions- Minerals have a definite composition; they are not a mixture of various amounts of ingredients.

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Elements

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are substances that cannot be broken down, some minerals are simple elements. Elements are the basic substances that are building blocks for all matter and there are 92 of them.

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Silicates

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Si, O
2

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SiO
2

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quartz

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Compounds

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Some minerals are componds. Compounds are materials made up of more than one kind of atom (element) combined chemically into larger units called molecules. The molecules are formed from atoms joined in very specific proportions.

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Minerals have an orderly arrangement of internal atoms

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Minerals are cyrstalline because their atoms and molecules are in a specific arrangement or pattern. This arrangement is called cystal structure. Each mineral has its own distinctive crystal structure which is repsonsible for many of its chemical and physical properties such as its hardness the way it breaks and its crystal form.

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Minerals and Rocks statement

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All minerals are rock but not all rocks are minerals.

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Rock Forming Minerals

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Many rocks are made up of minerals, but some rocks are also composed or organic or glassy materials that are not minerals. Although thousands of minerals exist, only a small number of these are comonly found in rocks. These 20-30 minerals are called the rock-forming minerals, and can be found in the chart called Properties of Common Minerals in the Earth Science Reference Tables.

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Mineral Formation

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Since all minerals are rocks, they form by processes that also create rocks.

-Percipitation from water caused by such processes as evaporation, chemical reactions, and temperature changes
-Cooling and solidification of magma
-Rearrangement of atoms in existing minerals under conditions of high temperature and pressure

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Properties of Minerals

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Each mineral has a characteristic set of physical and chemical properties that can be used to help identify it. These are largely determined by the minerals crystal structure and chemical compostition. The most accurate way to determine a minerals identify is to use x-ray diffraction and other methods that are not commonly available.

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Properties of Minerals 1

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1. Colore- Although the color of a mineral is one of its most obvious properties, in most cases it is not very helpful in identifying the mineral.

2. Streak- The streak of a mineral is the color of the powdered mineral. The streak is obtained by rubbing the unknown mineral on a strak plate which is an unglazed porelain tile. The color of the streak can different than the color of the mineral itself, and can tend to be more consistent than the apparent color of the mineral. Pyrite can be easily identified by its streak because while its color is similar to cold, its streak is black or dark green. Golds streak is gold.

3. Hardness- Hardness is a mineral resistance to being scratched. This is not the same as how easily it breaks! A diamond is the hardest mineral, but if you drop it on the floor it can shatter.

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Properties of Minerals 2

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4. Luster- Luster is the way a freshly cut surface of a mineral shines or doesnt shine. There are 2 broad categories of luster metallic and non-metallic. Minerals with metallic luster have a hard shiny look like polished metal. Examples are gold and silver jewelry, a newly minted penny or an aluminum can.

5. Density or Specific Gravity- We find the density of a substance by measuring its mass and its volume and dividing

Density= Mass/Volume

Specific Gravity+ Density of mineral/Density of Water

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Properties of Minerals 4

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7. Fracture- If a minerals crystal structure does not have these zones of weakness, then it will break unevenly leaving rough surfaces this is called fracture. Even though they do not follow a particular direction whenthey break, these minerals can display distinctive patterns when they fracture that can be very helpful to mineral indentification.
a. Conchoidal- the mineral break looks like a smooth, scooped out bowl. Observed in Quartz.
b. Splintery- little needles are formed at the break. Seen in hornblende.

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Crystal Structure

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The outward geometric shape of a mineral the crystal shape reflects the crystal structure. If crystals that form a mineral are allowed to grow freely then the mineral shape will have the smooth faces that mimic the crystal structure. Unfortunately crystals usually dont get to grow freely instead many crystals arer trying to grow in a small envirorment and the size and shape becomes limited. This means that the use of the crystal form is not very helpful when trying to identify minerals.

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Other Properites

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Chemical Properties
Magnetism
Smell
Acid Test

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Common Minerals

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Some of the most abundent elements on earth are Oxygen and Silicon. Some of the common MINERALS are Feldspars, Quartz, Micas, Amphiboles, Pyroxens, Calcite, Olivine, Clay.

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Identifying Minerals

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You need to be able to use the information in the Properties of Common Minerals chart to be able to identify minerals from written descriptions or form investigating the minerals yourself.

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Properties Of Minerals 3

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6. Cleavage- We test a minerals cleavage by breaking it. Cleavage is the tendency of a mineral to break alond zones of weakness. When this happens the break can form smooth to semi-smooth surfaces that often reflect light so they appear shindy. Whether or not a mineral will have these zones of weakness depends on its crystal structure.
a. Basal- The mineral splits into smooth flat sheets. The best example of this ist the mineral mica. under even modest amounts of stress mica will split into extremly thin transparent sheets. Early settlers in America used sheets of mica for windows.
b. Cubic- The mineral splits into cube or rectangular prism shapes. Halite or rock salt is an example of a mineral that has this kind of cleavage.
c. Rhombohedral- The mineral splits into prisms with rhombus or parallelogram faces. Calcite is an excellent example of a mineral with this kid of cleavage