Name_______________________________Date______________Work on the following lessons. Define the vocabulary terms and answer the questions in proper complete sentences. (when answering in proper complete sentences, restate the question then answer the question) This is due today 2/16/18 after class. Lesson Objectives Describe the characteristics that all minerals share.

Identify the groups in which minerals are classified and their characteristics.

*Give definition for the following vocabulary terms

Vocabulary chemical compound

crystal

inorganic

mineral

silicates

IntroductionMinerals are categorized based on their chemical composition. Owing to similarities in composition, minerals within a same group may have similar characteristics.

What is a Mineral?Minerals are everywhere! Figure below shows some common household items and the minerals used to make them. The salt you sprinkle on food is the mineral halite. Silver in jewelry is also a mineral. Baseball bats and bicycle frames both contain minerals. Although glass is not a mineral, it is produced from the mineral quartz. Scientists have

identified more than 4,000 minerals in Earth’s crust. A few are common, but many are uncommon.

Silver and halite are minerals; the mineral quartz is used to make glass.

Geologists have a very specific definition for minerals. A material is characterized as a mineral if it meets all of the following traits. A mineral is an inorganic, crystalline solid. A mineral is formed through natural processes and has a definite chemical composition. Minerals can be identified by their characteristic physical properties such as crystalline structure, hardness, density, flammability, and color.

Crystalline SolidMinerals are crystalline solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern (Figure below). The pattern of atoms in different samples of the same mineral is the same. Is glass a mineral? Without a crystalline structure, even natural glass is not a mineral.

Sodium ions (purple balls) bond with chloride ions (green balls) to make table salt (halite). All of the grains of salt that are in a salt shaker have this crystalline structure.

Inorganic SubstancesOrganic substances are the carbon-based compounds made by living creatures and include proteins, carbohydrates, and oils. Inorganic substances have a structure that is not characteristic of living bodies. Coal is made of plant and animal remains. Is it a mineral? Coal is a classified as a sedimentary rock but is not a mineral.

Natural ProcessesMinerals are made by natural processes, those that occur in or on Earth. A diamond created deep in Earth’s crust is a mineral. Is a diamond created in a laboratory by placing carbon under high pressures a mineral? No. Do not buy a laboratory-made “diamond” for jewelry without realizing it is not technically a mineral.

Chemical CompositionNearly all (98.5%) of Earth’s crust is made up of only eight elements – oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium – and these are the elements that make up most minerals.

All minerals have a specific chemical composition. The mineral silver is made up of only silver atoms and diamond is made only of carbon atoms, but most minerals are made up of chemical compounds. Each mineral has its own chemical formula. Halite, pictured in the Figure above, is NaCl (sodium chloride). Quartz is always made of two oxygen atoms bonded to a silicon atom, SiO2. If a mineral contains any other elements in its crystal structure, it's not quartz.

A hard mineral containing covalently bonded carbon is diamond, but a softer mineral that also contains calcium and oxygen along with carbon is calcite (Figure below).

The structure of calcite shows the relationship of calcium (Ca), carbon (C), and oxygen (O).

Some minerals have a range of chemical composition. Olivine always has silicon and oxygen as well as iron or magnesium or both, (Mg, Fe)2SiO4.

Physical PropertiesThe physical properties of minerals include:

Color: the color of the mineral.

Streak: the color of the mineral’s powder.

Luster: the way light reflects off the mineral’s surface.

Specific gravity: how heavy the mineral is relative to the same volume of water.

Cleavage: the mineral’s tendency to break along flat surfaces.

Fracture: the pattern in which a mineral breaks.

Hardness: what minerals it can scratch and what minerals can scratch it.

How physical properties are used to identify minerals is described in the lesson on Mineral Formation.

Mineral GroupsMinerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups.

Silicate MineralsThe roughly 1,000 silicate minerals make up over 90% of Earth's crust. Silicates are by far the largest mineral group. Feldspar and quartz are the two most common silicate minerals. Both are extremely common rock-forming minerals.

The basic building block for all silicate minerals is the silica tetrahedron, which is illustrated in Figure below. To create the wide variety of silicate minerals, this pyramid-shaped structure is often bound to other elements, such as calcium, iron, and magnesium.

One silicon atom bonds to four oxygen atoms to form a silica tetrahedron.

Silica tetrahedrons combine together in six different ways to create different types of silicates (Figure below). Tetrahedrons can stand alone, form connected circles called rings, link into single and double chains, form large flat sheets of pyramids, or join in three dimensions.

The different ways that silica tetrahedrons can join together cause these two minerals to look very different.

Native ElementsNative elements contain atoms of only one type of element. Only a small number of minerals are found in this category. Some of the minerals in this group are rare and valuable. Gold, silver, sulfur, and diamond are examples of native elements.

CarbonatesThe basic carbonate structure is one carbon atom bonded to three oxygen atoms. Carbonates include other elements, such as calcium, iron, and copper. Calcite (CaCO3) is the most common carbonate mineral (Figure below).

Calcite is the most common carbonate mineral.

Azurite and malachite, shown in the Figure below, are carbonates that contain copper instead of calcium.

Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite.

HalidesHalide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt is not the only halide. The chemical elements known as the

halogens (fluorine, chlorine, bromine, or iodine) bond with various metallic atoms to make halide minerals (see Figure below).

Fluorite is a halide containing calcium and fluorine.

OxidesOxides contain one or two metal elements combined with oxygen. Many important metals are found as oxides. Hematite (Fe2O3), with two iron atoms to three oxygen atoms, and magnetite (Fe3O4) (Figure below), with three iron atoms to four oxygen atoms, are both iron oxides.

Magnetite is the most magnetic mineral. Magnetite attracts or repels other magnets.

Phosphates

Phosphate minerals are similar in atomic structure to the silicate minerals. In the phosphates, phosphorus, arsenic, or vanadium bond to oxygen to form a tetrahedra. There are many different minerals in the phosphate group, but most are rare (Figure below).

Turquoise is a phosphate mineral containing copper, aluminum, and phosphorus.

SulfatesSulfate minerals contain sulfur atoms bonded to oxygen atoms. Like halides, they form where salt water evaporates. The sulfate group contains many different minerals, but only a few are common.

Gypsum is a common sulfate with a variety of appearances (Figure below). Some gigantic 11-meter gypsum crystals have been found. That is about as long as a school bus!

Although the orange crystals on the left looks nothing like the white sands on the right, both the crystals and sands are gypsum.

SulfidesSulfides are formed when metallic elements combine with sulfur. Unlike sulfates, sulfides do not contain oxygen. Pyrite, or iron sulfide, is a common sulfide mineral known as fool’s gold. People may mistake pyrite for gold because the two minerals are shiny, metallic, and yellow in color.

Lesson Summary For a substance to be a mineral, it must be a naturally occurring, inorganic,

crystalline solid that has a characteristic chemical composition and crystal structure.

The atoms in minerals are arranged in regular, repeating patterns that can be used to identify that mineral.

Minerals are divided into groups based on their chemical composition.

The chemical feature of each groups is: native elements – only one element; silicates – silica tetrahedron; phosphates – phosphate tetrahedron; carbonates – one carbon atom with three oxygen atoms; halides – a halogen bonded with a metallic atom; oxides – a metal combined with oxygen; sulfates – sulfur and oxygen; sulfides – metal with sulfur, no oxygen.

Review Questions-Answer Each Question in Proper Complete Sentences1. What is a crystal?

2. Which elements do all silicate minerals contain?

3. Obsidian is a glass that forms when lava cools so quickly that the atoms do not have a chance to arrange themselves in crystals. Is obsidian a crystal? Explain your reasoning.

4. What are the eight major mineral groups?

5. What is the same about all minerals in the silicate group? What is different about them?

6. One sample has a chemical composition with a ratio of two iron atoms to three oxygen atoms. Another sample has a chemical composition with a ratio of three iron atoms to four oxygen atoms. They contain the same elements: Are they the same mineral?

7. How does the native elements mineral group differ from all of the other mineral groups?

8. On a trip to the natural history museum you find two minerals that are similar in color. You can see from their chemical formulas that one mineral contains the elements zinc, carbon, and oxygen. The other mineral contains the elements zinc, silicon, oxygen, and hydrogen. Your friend tells you that the minerals are in the same mineral group. Do you agree? Explain your reasoning.

3.3 Mineral IdentificationDifficulty Level: Basic | Created by: CK-12

Lesson Objectives Explain how minerals are identified.

Describe how color, luster, and streak are used to identify minerals.

Summarize specific gravity.

Explain how the hardness of a mineral is measured.

Describe the properties of cleavage and fracture.

Identify additional properties that can be used to identify some minerals.

VocabularyGive definition for the following vocabulary terms

Cleavage

Density

Fracture

Hardness

Luster

Mineralogist

Streak

IntroductionMinerals can be identified by their physical characteristics. The physical properties of minerals are related to their chemical composition and bonding. Some characteristics, such as a mineral's hardness, are more useful for mineral identification. Color is readily observable and certainly obvious, but it is usually less reliable than other physical properties.

How are Minerals Identified?Mineralogists are scientists who study minerals. One of the things mineralogists must do is identify and categorize minerals. While a mineralogist might use a high-powered microscope to identify some minerals, most are recognizable using physical properties.

Check out the mineral in Figure below. What is the mineral’s color? What is its shape? Are the individual crystals shiny or dull? Are there lines (striations) running across the minerals? In this lesson, the properties used to identify minerals are described in more detail.

This mineral has shiny, gold, cubic crystals with striations, so it is pyrite.

Color, Streak, and Luster

Diamonds are popular gemstones because the way they reflect light makes them very sparkly. Turquoise is prized for its striking greenish-blue color. Notice that specific terms are being used to describe the appearance of minerals.

ColorColor is rarely very useful for identifying a mineral. Different minerals may be the same color. Real gold, as seen in Figure below, is very similar in color to the pyrite in Figure above.

This mineral is shiny, very soft, heavy, and gold in color, and is actually gold.

The same mineral may also be found in different colors. Figure below shows one sample of quartz that is colorless and another quartz that is purple. A tiny amount of iron makes the quartz purple. Many minerals are colored by chemical impurities.

Purple quartz, known as amethyst, and clear quartz are the same mineral despite the different colors.

StreakStreak is the color of a mineral’s powder. Streak is a more reliable property than color because streak does not vary. Minerals that are the same color

may have a different colored streak. Many minerals, such as the quartz in the Figure above, do not have streak.

To check streak, scrape the mineral across an unglazed porcelain plate (Figure below). Yellow-gold pyrite has a blackish streak, another indicator that pyrite is not gold, which has a golden yellow streak.

The streak of hematite across an unglazed porcelain plate is red-brown.

LusterLuster describes the reflection of light off a mineral’s surface. Mineralogists have special terms to describe luster. One simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such as pyrite, have a metallic luster. Minerals such as quartz have a non-metallic luster. Different types of non-metallic luster are described in Table below.

Six types of non-metallic luster.

Luster Appearance

Adamantine Sparkly

Earthy Dull, clay-like

Pearly Pearl-like

Resinous Like resins, such as tree sap

Six types of non-metallic luster.

Luster Appearance

Silky Soft-looking with long fibers

Vitreous Glassy

Can you match the minerals in Figure below with the correct luster from Table above?

(a) Diamond has an adamantine luster. (b) Quartz is not sparkly and has a vitreous, or glassy, luster. (b) Sulfur reflects less light than quartz, so it has a resinous luster.

Specific GravityDensity describes how much matter is in a certain amount of space: density = mass/volume.

Mass is a measure of the amount of matter in an object. The amount of space an object takes up is described by its volume. The density of an object depends on its mass and its volume. For example, the water in a drinking glass has the same density as the water in the same volume of a swimming pool.

Gold has a density of about 19 g/cm3; pyrite has a density of about 5 g/cm3 - that’s another way to tell pyrite from gold. Quartz is even less dense than pyrite and has a density of 2.7 g/cm3.

The specific gravity of a substance compares its density to that of water. Substances that are more dense have higher specific gravity.

HardnessHardness is a measure of whether a mineral will scratch or be scratched. Mohs Hardness Scale, shown in Table below, is a reference for mineral hardness.

Mohs Hardness Scale: 1 (softest) to 10 (hardest).

Hardness Mineral

1 Talc

2 Gypsum

3 Calcite

4 Fluorite

5 Apatite

6 Feldspar

7 Quartz

8 Topaz

9 Corundum

10 Diamond

With a Mohs scale, anyone can test an unknown mineral for its hardness. Imagine you have an unknown mineral. You find that it can scratch fluorite or even apatite, but feldspar scratches it. You know then that the mineral’s hardness is between 5 and 6. Note that no other mineral can scratch diamond.

Cleavage and Fracture

Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways.

Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite breaks between layers of sodium and chlorine to form cubes with smooth surfaces (Figure below).

A close-up view of sodium chloride in a water bubble aboard the International Space Station.

Mica has cleavage in one direction and forms sheets (Figure below).

Sheets of mica.

Minerals can cleave into polygons. Fluorite forms octahedrons (Figurebelow).

This rough diamond shows its octahedral cleavage.

One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces.

Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral.

Minerals may have characteristic fractures (Figure below). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture.

Chrysotile has splintery fracture.

Other Identifying CharacteristicsSome minerals have other unique properties, some of which are listed in Table below. Can you name a unique property that would allow you to instantly identify a mineral that’s been described quite a bit in this chapter? (Hint: It is most likely found on your dinner table.)

 

Some minerals have unusual properties that can be used for identification.

Property Description Example of Mineral

Fluorescence

Mineral glows under ultraviolet light Fluorite

Magnetism Mineral is attracted to a magnet Magnetite

Some minerals have unusual properties that can be used for identification.

Property Description Example of Mineral

RadioactivityMineral gives off radiation that can be measured with Geiger counter

Uraninite

ReactivityBubbles form when mineral is exposed to a weak acid

Calcite

Smell Some minerals have a distinctive smellSulfur (smells like rotten eggs)

Taste Some minerals taste salty Halite

A simple lesson on how to identify minerals is seen in this video: http://www.youtube.com/watch?v=JeFVwqBuYl4.

Lesson Summary Minerals have distinctive properties that can be used to help identify them.

Color and luster describe the mineral’s outer appearance. Streak is the color of the powder.

A mineral has a characteristic density.

Mohs Hardness Scale is used to compare the hardness of minerals.

Cleavage or the characteristic way a mineral breaks depends on the crystal structure of the mineral.

Some minerals have special properties that can be used to help identify them.

Review Questions-Answer each question in proper complete sentences1. Which properties of a mineral describe the way it breaks apart?

2. A mineral looks dry and chalky. What sort of luster does it have?

3. What causes a mineral to have the properties that it has?

4. Apatite scratches the surface of an unknown mineral. Which mineral would you use next to test the mineral’s hardness — fluorite or feldspar? Explain your reasoning.

5. Why is streak more reliable than color when identifying a mineral?

6. Mineral A has a density of 5 g/cm3. Mineral B is twice as dense as Mineral A. What is the density of Mineral B?

7. Why do some minerals cleave along certain planes?